Exposure & Technical Factors

2.1 Kilovoltage Peak (kVp)

Kilovoltage peak (kVp) is the maximum potential difference applied across the X-ray tube during an exposure. It is one of the most important controls affecting the characteristics of the X-ray beam.

The selected kVp influences:

• Maximum photon energy
• Average photon energy
• Beam penetration
• X-ray output
• Subject contrast
• Detector exposure
• Patient dose
• The ability of the beam to pass through different tissues

What does kVp actually control? The electrical potential difference between the cathode and anode determines the energy with which electrons strike the target.

When kVp is increased:

Higher tube voltage → higher electron energy → higher maximum X-ray photon energy

The resulting beam is generally more penetrating. It is important to distinguish between maximum photon energy and average photon energy. The maximum photon energy is directly related to the selected kVp. However, the X-ray beam contains a spectrum of photon energies, so increasing kVp also changes the distribution of photon energies and generally increases the mean beam energy.

2.1.1 kVp and Beam Penetration

Higher-energy photons are more capable of passing through the patient. Increasing kVp therefore generally increases beam penetration.

For example, the kVp selected for a chest examination is substantially higher than that used for many small extremity examinations because the thorax contains a greater thickness and range of tissues that the beam must penetrate.

However, penetration should not be considered independently of patient size. A larger patient may require a different technique from a smaller patient even when the same anatomical examination is being performed.

2.1.2 kVp and X-Ray Quantity

Although kVp is primarily associated with beam quality, increasing kVp also increases X-ray output. This is because higher tube voltage increases the efficiency of X-ray production as well as the energy of the resulting photons.

Consequently:

Increasing kVp generally increases both beam energy and X-ray output.

This is an important distinction from mAs, which primarily controls the quantity of electrons crossing the tube and therefore the number of X-ray photons produced.

2.1.3 kVp and Image Contrast

kVp has an important influence on subject contrast. At relatively lower kVp, there is generally a greater difference in attenuation between tissues, which can produce greater subject contrast. At higher kVp, the beam is more penetrating and the relative difference in attenuation between tissues tends to decrease, generally producing lower subject contrast.

However, modern digital radiography complicates the traditional concept of "image contrast". Digital image processing can substantially modify displayed contrast. Therefore:

kVp influences the physical formation of the image, while post-processing influences how that image is displayed.

The radiographer should not rely on digital processing to compensate for inappropriate kVp selection.

2.1.4 kVp and Patient Thickness

Patient thickness is an important consideration when selecting kVp. As patient thickness increases:

• more photons are attenuated
• fewer photons reach the detector
• scatter may increase
• a more penetrating beam may be required

The appropriate adjustment depends on the examination and local technique chart. Patient thickness should therefore be considered alongside:

• kVp
• mAs
• grid use
• SID
• AEC
• detector characteristics

2.1.5 kVp and Patient Dose

The relationship between kVp and patient dose is not simple because changing kVp may be accompanied by a change in mAs.

Increasing kVp can increase X-ray output substantially. However, in some technique-selection approaches, an increase in kVp may allow a reduction in mAs while maintaining an appropriate detector exposure.

Therefore:

Higher kVp does not automatically mean higher patient dose in every clinical situation.

Dose depends on the complete exposure strategy, including:

• kVp
• mAs
• filtration
• patient size
• field size
• grid
• SID
• AEC
• examination type

2.1.6 kVp and Detector Exposure

Increasing kVp generally increases the amount and energy of radiation reaching the detector, assuming all other factors remain unchanged.

If kVp is increased without adjusting other factors:

• detector exposure generally increases
• image noise may decrease
• patient exposure may increase

If kVp is increased while mAs is appropriately reduced, detector exposure may be maintained while altering the energy distribution of the beam. This principle is important when considering exposure optimisation.

2.1.7 kVp and Scatter Radiation

As kVp increases, the proportion of radiation reaching the detector as scatter can become an important consideration. Scatter reduces image contrast.

Scatter can be controlled through:

• appropriate collimation
• appropriate patient positioning
• grids where clinically justified
• air-gap techniques in selected situations
• appropriate exposure selection

The use of a higher kVp therefore needs to be considered alongside scatter management.

2.1.8 kVp and Beam Quality

Beam quality describes the penetrating characteristics of the X-ray beam. It is influenced by:

• kVp
• filtration
• target material
• generator waveform

Increasing kVp generally increases beam quality by increasing average photon energy. Increasing filtration also increases effective beam energy by preferentially removing lower-energy photons.

Therefore:

kVp and filtration both influence beam quality, but through different mechanisms.

2.1.9 kVp and Exposure Technique Selection

The appropriate kVp is determined by the complete clinical situation. Important considerations include:

• anatomical region
• patient thickness
• clinical indication
• presence of pathology
• detector system
• grid use
• SID
• AEC availability
• equipment characteristics
• local technique charts
• radiation-protection requirements

There is no single universal kVp for a particular examination. For educational purposes, typical technique ranges may be provided elsewhere in Global Radiographers, but these should always be identified as illustrative rather than mandatory values. Actual exposure factors should follow the equipment manufacturer's guidance and local technique charts.

2.1.10 kVp and the 15% Concept

Radiographic education traditionally describes a 15% rule, in which increasing kVp by approximately 15% can approximately double detector exposure under certain conditions. Conversely, reducing kVp by approximately 15% can approximately halve detector exposure.

This is a useful educational relationship, but it should not be treated as a universal law or a substitute for an equipment-specific technique chart. The actual relationship depends on:

• generator characteristics
• filtration
• tube design
• detector response
• exposure conditions
• patient attenuation

The 15% concept is therefore best understood as a technique-selection principle rather than an exact clinical formula.

2.1.11 kVp and the Diagnostic Task

The optimum kVp is the value that provides sufficient penetration and appropriate image information for the clinical question without unnecessary exposure.

For example:

• high penetration is important in chest imaging
• sufficient penetration is required for abdominal and pelvic imaging
• lower-energy techniques may be appropriate for selected extremity examinations
• specialised projections may require adjustment according to anatomy and geometry

The appropriate kVp is therefore determined by the anatomy, clinical task and imaging system, rather than by anatomy alone.

2.2 Tube Current — mA

Tube current (mA) represents the rate at which electrons flow from the cathode to the anode during an exposure. Increasing mA generally increases the number of electrons crossing the tube per unit time and therefore increases the number of X-ray photons produced.

Increasing mA generally:

• increases X-ray quantity
• increases detector exposure
• increases patient exposure if other factors remain unchanged
• does not directly determine maximum photon energy

mA should therefore be distinguished from kVp.

kVp primarily influences beam energy and penetration.

mA primarily influences the rate of X-ray photon production.

2.3 Milliampere-Seconds — mAs

mAs represents the product of tube current and exposure time.

mAs = mA × exposure time

For example:

200 mA × 0.05 s = 10 mAs

and:

100 mA × 0.10 s = 10 mAs

produce the same nominal mAs. Under otherwise comparable conditions, increasing mAs generally increases the number of X-ray photons produced.

Increasing mAs generally:

• increases photon quantity
• increases detector exposure
• reduces quantum noise
• increases patient radiation exposure

mAs is therefore an important tool for controlling the quantity of radiation used for an examination. However, mAs should never be considered in isolation. The actual image and patient dose also depend on:

• kVp
• filtration
• patient thickness
• SID
• grid
• AEC
• detector efficiency

2.4 mAs and Image Noise

Insufficient radiation reaching the detector can increase quantum noise. Increasing mAs increases the number of photons available for image formation and can improve the signal-to-noise relationship.

However, increasing mAs solely to produce a visually "cleaner" image is not appropriate if the additional exposure does not provide meaningful diagnostic benefit.

The appropriate balance is:

sufficient signal for the diagnostic task + appropriate radiation optimisation

2.5 Exposure Time

Exposure time determines how long the X-ray tube produces radiation. Exposure time is particularly important because patient movement can degrade image sharpness.

Short exposure times are useful for:

• chest radiography
• paediatric imaging
• trauma
• patients unable to remain still
• portable examinations
• imaging anatomy affected by physiological motion

Reducing exposure time can reduce motion blur, provided sufficient tube current can be used to maintain the required mAs.

2.6 mA, mAs and Exposure Time

mA and exposure time can be varied while maintaining the same mAs.

For example:

100 mA × 0.10 s = 10 mAs

200 mA × 0.05 s = 10 mAs

400 mA × 0.025 s = 10 mAs

This allows the radiographer to select an appropriate combination of tube current and time. For examinations where motion is a concern, a higher mA with a shorter exposure time may be advantageous, provided that the tube, generator and equipment can safely support the selected exposure.

2.7 Source-to-Image Distance — SID

Source-to-image distance (SID) is the distance between the X-ray tube focal spot and the image receptor.

SID affects:

• image magnification
• geometric sharpness
• radiation intensity at the detector
• exposure requirements
• image geometry

Increasing SID generally reduces magnification when other geometric factors remain unchanged.

2.7.1 SID and Magnification

Image magnification is influenced by the relationship between:

• source-to-object distance
• object-to-image distance
• source-to-image distance

Increasing SID generally reduces magnification because the beam becomes less divergent at the object-image relationship. This is one reason why longer SID is used for examinations where reduction of magnification is important.

2.7.2 SID and Chest Radiography

Chest radiography commonly uses a relatively long SID, often approximately 180 cm (72 inches), depending on equipment and local protocol. The longer distance helps reduce magnification of the heart and mediastinal structures compared with a shorter SID. The exact SID should follow the local examination protocol and equipment configuration.

2.7.3 SID and Radiation Intensity

According to the inverse-square relationship, radiation intensity decreases as distance from the source increases. Consequently, changing SID changes the radiation intensity incident on the detector.

If SID is changed substantially while other exposure factors remain unchanged, the detector exposure may also change. Exposure compensation may therefore be required according to the equipment and technique chart.

2.8 Object-to-Image Distance — OID

Object-to-image distance (OID) is the distance between the anatomical structure being imaged and the image receptor. OID has a major influence on image geometry.

Increasing OID generally:

• increases magnification
• increases geometric unsharpness
• can alter the apparent shape and size of anatomy

Where possible, the anatomical structure should be positioned close to the detector.

2.8.1 OID and Magnification

X-ray beams diverge from the focal spot. When the anatomy is separated from the detector, the beam has greater opportunity to diverge before reaching the detector.

Therefore:

Greater OID → greater magnification

This effect is particularly relevant when accurate anatomical size and geometry are important.

2.8.2 OID and Spatial Resolution

Increasing OID can increase geometric unsharpness. This occurs because the finite focal spot produces a region of penumbra at the image receptor. Reducing OID generally improves geometric sharpness.

The combination of:

small focal spot + low OID + appropriate SID

is therefore favourable for high spatial resolution.

2.9 Focal Spot

The focal spot is the effective area of the anode target from which useful X-rays appear to originate. Focal-spot size influences geometric unsharpness and therefore spatial resolution.

Small focal spot

Advantages:

• improved spatial resolution
• reduced geometric unsharpness
• improved visualisation of fine detail

Limitations:

• lower permissible tube loading
• greater thermal limitation

Large focal spot

Advantages:

• greater tube loading capability
• better management of high heat loads

Limitations:

• greater geometric unsharpness
• potentially reduced spatial resolution

The smallest focal spot capable of safely handling the required exposure should be selected when clinically appropriate.

2.10 Geometric Unsharpness

Geometric unsharpness is influenced principally by:

• focal-spot size
• OID
• SID

A simplified relationship is:

Geometric unsharpness ∝ focal spot size × OID / SOD

where:

SOD = source-to-object distance

This demonstrates why:

• smaller focal spots improve sharpness
• smaller OID improves sharpness
• greater SOD generally reduces geometric unsharpness

2.11 Beam Angulation

The central ray may need to be angled for particular projections. Beam angulation can influence:

• anatomical superimposition
• shape distortion
• spatial relationships
• apparent length of structures
• positioning accuracy

Incorrect angulation can result in:

• elongation
• foreshortening
• altered anatomical relationships
• failure to demonstrate the intended structure

Beam angulation should therefore be based on the specific examination and clinical objective.

2.12 Inverse Square Law

The inverse-square law describes how radiation intensity changes with distance from a point source. It can be expressed as:

I₁ / I₂ = (D₂ / D₁)²

where:

• I₁ = intensity at distance D₁
• I₂ = intensity at distance D₂
• D₁ and D₂ = distances from the radiation source

Example: If the distance from the source is doubled:

D₂ = 2D₁

then:

I₂ = I₁ / 4

Therefore, the intensity becomes approximately one-quarter of the original value. If the distance is reduced by half, the intensity increases by approximately four times.

2.12.1 Clinical Importance

The inverse-square law is important for:

• exposure-factor adjustment
• SID changes
• mobile radiography
• fluoroscopy
• operating theatre imaging
• staff radiation protection

It is particularly important when working with mobile X-ray equipment because increasing the distance between personnel and the radiation source can substantially reduce occupational exposure.

2.13 Exposure Compensation for Changes in Distance

When SID changes, detector exposure changes because of the inverse-square relationship. If maintaining similar detector exposure is required, the exposure factor may need to be adjusted.

The relationship can be represented as:

mAs₁ / mAs₂ = (SID₁ / SID₂)²

or equivalently:

mAs₂ = mAs₁ × (SID₂ / SID₁)²

This relationship is useful for understanding technique changes, although clinical exposure selection should follow the equipment-specific technique chart whenever available.

2.14 Patient Thickness and Body Habitus

Patient size has a major effect on X-ray attenuation. As tissue thickness increases:

• more photons are absorbed or scattered
• fewer photons reach the detector
• greater beam penetration may be required
• scatter may increase
• exposure requirements may change

Body habitus can therefore influence technique selection. However, patient thickness is more useful than appearance alone when determining the technical requirement.

2.15 Grid Selection and Exposure Factors

A grid reduces scatter reaching the detector but also absorbs some primary radiation. Consequently, grid use may require increased exposure.

The effect depends on:

• grid ratio
• grid frequency
• patient thickness
• kVp
• detector technology
• SID
• centring
• clinical examination

The radiographer should select the appropriate grid according to the examination and local protocol rather than applying a grid routinely.

2.16 Automatic Exposure Control and Technical Factors

AEC can automatically terminate an exposure when sufficient radiation reaches the sensing system. AEC can reduce the need for manual exposure-time selection, but it does not eliminate the need for appropriate technical judgement.

Correct:

• chamber selection
• patient positioning
• centring
• collimation
• anatomical coverage
• patient preparation

remain essential. Incorrect positioning over an AEC chamber can result in inappropriate exposure.

2.17 Technique Charts

A technique chart provides recommended exposure ranges for specific examinations. It may include:

• kVp
• mAs
• mA
• exposure time
• SID
• grid requirements
• AEC selection
• detector selection

Technique charts are usually developed for a particular imaging system and should be considered equipment-specific. They may need adjustment when:

• equipment changes
• detector technology changes
• processing systems change
• patient populations change
• dose audits identify a need for optimisation

A technique chart should therefore be regarded as a controlled clinical optimisation tool, not a universal set of exposure numbers.

2.18 Relationship Between the Main Exposure Factors

The major technical factors should be considered together.

2.19 Optimising Exposure Factors

Exposure optimisation involves balancing several competing requirements. The radiographer should consider:

Diagnostic information

against

Patient radiation exposure

while also considering:

Image quality + patient condition + equipment limitations + clinical indication

An exposure should not be increased simply because a higher exposure produces a visually smoother image. Similarly, reducing exposure below an appropriate level can increase noise and potentially compromise diagnostic information.

The appropriate exposure is therefore the one that is sufficient for the clinical task and appropriately optimised, rather than simply the lowest numerical exposure.

Key Learning Points

At the end of this topic, the learner should be able to:

1. Define kVp and explain its effect on X-ray beam energy.
2. Explain the relationship between kVp and beam penetration.
3. Explain how kVp influences subject contrast.
4. Explain the difference between beam quality and X-ray quantity.
5. Describe the relationship between mA, exposure time and mAs.
6. Explain how mAs affects photon quantity and image noise.
7. Explain why short exposure times are useful for reducing motion.
8. Define SID and explain its effect on magnification and radiation intensity.
9. Define OID and explain its effect on magnification and geometric unsharpness.
10. Explain the importance of focal-spot selection.
11. Explain geometric unsharpness.
12. Apply the inverse-square law to changes in distance.
13. Explain how patient thickness influences technique selection.
14. Explain how grids affect exposure requirements.
15. Explain the principles and limitations of AEC.
16. Understand the role of equipment-specific technique charts.
17. Recognise that exposure factors must be considered as an interconnected system.
18. Apply optimisation principles to achieve appropriate diagnostic information without unnecessary radiation exposure.

Radiographic Positioning Principles

3.1 Anatomical Position

The anatomical position is the standard reference position used to describe anatomical relationships and movements.

In the anatomical position:

• The patient is standing upright.
• The head and eyes face forward.
• The arms are positioned alongside the body.
• The palms face forwards.
• The feet are directed forwards.

This reference position remains useful even when the patient is being examined in another position. For example, terms such as anterior, posterior, medial, lateral, proximal and distal are described relative to standard anatomical orientation rather than the patient's temporary position.

Important directional terms:

Consistent terminology is particularly important when communicating with radiologists, clinicians and other members of the healthcare team.

3.2 Body Planes

Body planes are imaginary surfaces used to describe the orientation and division of the body. Understanding these planes helps the radiographer describe anatomy, positioning and the direction of imaging.

Sagittal Plane: The sagittal plane divides the body into right and left portions. The midsagittal plane passes through the midline and divides the body into approximately equal right and left halves.

Coronal Plane: The coronal plane divides the body into anterior and posterior portions. It is also commonly called the frontal plane.

Transverse Plane: The transverse plane, also called the axial or horizontal plane, divides the body into superior and inferior portions.

Although these planes are commonly associated with cross-sectional imaging, they are also important in understanding radiographic positioning and beam orientation.

3.3 Body Axes

Body axes provide another way of describing orientation and movement. The principal axes are:

• Longitudinal axis — generally runs from superior to inferior.
• Transverse axis — generally runs from side to side.
• Anteroposterior axis — generally runs from anterior to posterior.

Understanding planes and axes helps explain movements such as:

• rotation
• flexion
• extension
• abduction
• adduction
• internal rotation
• external rotation

These movements are frequently used when positioning limbs and joints.

3.4 Common Patient Positions

The patient's position describes how the body is arranged relative to gravity, the examination table and the detector.

Erect: The patient is upright, either standing or seated. Commonly used for:

• chest radiography
• abdominal examinations
• weight-bearing studies
• selected spinal examinations
• some extremity examinations

Supine: The patient lies on the back with the anterior surface facing upwards. Commonly used for:

• abdominal radiography
• trauma imaging
• pelvic imaging
• portable radiography
• patients unable to stand

Prone: The patient lies on the abdomen with the posterior surface facing upwards. Used for selected examinations and projections where clinically appropriate.

Seated: The patient is positioned sitting, usually on a chair, examination stool or other support. This may be used when the patient cannot stand safely.

Recumbent: Recumbent describes a patient lying down. It may be further specified as:

• supine
• prone
• lateral

The term is particularly useful when the patient's exact position needs to be described in clinical documentation.

Lateral: The patient is positioned with one side of the body against or parallel to the detector. A lateral projection may be obtained with the patient's:

• right side closest to the detector
• left side closest to the detector

The side should be clearly identified where relevant.

Oblique: The patient or anatomical part is rotated so that it is neither directly AP/PA nor directly lateral. Oblique positioning is used to separate anatomical structures that would otherwise overlap.

Decubitus: A decubitus position is a recumbent position in which the patient's body is rotated so that a specified side is dependent. The term should be accompanied by the relevant side and orientation where necessary.

For example:

• right lateral decubitus
• left lateral decubitus

Decubitus positioning can be particularly useful for demonstrating:

• air-fluid levels
• free intraperitoneal air
• pleural fluid
• other positional changes

3.5 Projection Terminology

A projection describes the direction in which the central X-ray beam passes through the patient and reaches the image receptor. This is different from describing the patient's position.

Common projections:

AP — Anteroposterior: The X-ray beam enters the anterior surface and exits through the posterior surface before reaching the detector.

PA — Posteroanterior: The beam enters through the posterior surface and exits through the anterior surface.

Lateral: The beam passes from one side of the body to the other.

Oblique: The beam passes through the body at an angle relative to a standard AP/PA or lateral projection.

Axial: The central ray is angled along or approximately along the long axis of a structure, depending on the examination.

3.6 Position Versus Projection

The terms position and projection should not be treated as interchangeable.

For example, a patient may be standing erect while a radiograph is obtained using a PA projection. Similarly, a patient may be supine while an AP projection is obtained.

Therefore:

Position = how the patient or anatomical part is arranged.

Projection = the direction of the X-ray beam through the anatomy.

This distinction is important throughout radiographic practice.

3.7 Central Ray

The central ray (CR) is the central portion of the primary X-ray beam. The central ray is used as the reference point for:

• centring
• beam direction
• beam angulation
• detector alignment
• anatomical positioning

Each radiographic projection has a defined or recommended central-ray location and direction. Correct CR placement helps ensure that the intended anatomy is appropriately demonstrated.

3.8 Central-Ray Angulation

The central ray may be directed perpendicular to the detector or angled according to the requirements of a particular projection.

Angulation may be:

• cephalic
• caudal
• medial
• lateral
• oblique
• compound

The exact direction and degree of angulation depend on the examination. Incorrect angulation can change the apparent shape and relationships of anatomical structures.

3.9 Centring

Centring refers to aligning the central ray with the appropriate anatomical landmark and detector.

Accurate centring helps:

• include the required anatomy
• maintain appropriate geometry
• reduce unnecessary field size
• support reproducibility
• ensure appropriate use of AEC where applicable

Poor centring can lead to:

• anatomy being excluded
• unnecessary irradiation
• increased distortion
• inappropriate AEC exposure
• difficulty comparing with previous examinations

Centring should therefore be considered together with detector positioning and collimation.

3.10 Anatomical Landmarks

Radiographic positioning relies heavily on palpable or visible anatomical landmarks. Landmarks help the radiographer determine:

• the location of the anatomy of interest
• the central-ray position
• detector placement
• collimation boundaries
• body-part alignment

Common examples include:

• external auditory meatus
• orbital margins
• mastoid processes
• vertebral prominences
• sternal angle
• iliac crests
• anterior superior iliac spines
• greater trochanters
• patella
• malleoli

The exact landmark used depends on the examination. Knowledge of surface anatomy is therefore essential for accurate positioning.

3.11 Rotation

Rotation occurs when the patient's body or anatomical part is turned around its longitudinal or another relevant axis. Rotation can substantially alter the appearance of anatomy.

It may:

• change anatomical relationships
• create asymmetry
• produce apparent displacement
• alter joint-space appearance
• affect measurements
• compromise image comparison

The radiographer should assess for rotation before exposure and confirm positioning after exposure using appropriate anatomical criteria.

3.12 Avoiding Unwanted Rotation

The method used to prevent rotation depends on the examination. The radiographer may use:

• patient instruction
• anatomical alignment
• positioning aids
• detector positioning
• tube alignment
• comparison of symmetrical anatomical structures

For example, symmetry of selected bony landmarks can help identify rotation on chest, pelvis and spinal examinations.

3.13 Detector / Image Receptor Positioning

The detector must be positioned so that the required anatomy is fully included. The radiographer should consider:

• detector size
• anatomical coverage
• detector orientation
• patient anatomy
• central-ray position
• SID
• collimation
• patient movement

The detector should be aligned appropriately with the anatomy and central ray. When a large anatomical region is being examined, detector size and orientation should be selected to minimise the need for repeat imaging.

3.14 Detector Orientation

Detectors may be positioned:

• longitudinally
• transversely
• vertically
• horizontally

The orientation should match the anatomy and projection. Incorrect orientation can result in:

• anatomy being clipped
• unnecessary exposure
• poor positioning
• repeat examination

Modern digital systems may use wireless or fixed detectors, but the fundamental positioning principles remain unchanged.

3.15 Source-to-Image Distance

SID is the distance from the focal spot of the X-ray tube to the image receptor. SID affects radiographic geometry and radiation intensity. Positioning decisions should therefore consider the required SID for the examination.

Longer SID generally:

• reduces magnification
• can improve geometric accuracy
• changes radiation intensity at the detector

The prescribed SID should follow the examination protocol and equipment configuration.

3.16 Object-to-Image Distance

OID is the distance between the anatomical structure being examined and the image receptor. Where possible, the anatomy should be positioned close to the detector.

Increasing OID generally increases:

• magnification
• geometric unsharpness

OID becomes particularly important when accurate representation of anatomical size and shape is required.

3.17 Beam Divergence and Positioning

X-rays diverge from the focal spot. This means that the position of the anatomy relative to the tube and detector affects the final image. The radiographer must therefore consider:

• SID
• OID
• central-ray direction
• part positioning
• detector alignment

These geometric relationships influence magnification, distortion and spatial sharpness.

3.18 Parallel and Perpendicular Alignment

For many routine projections, the anatomical structure and image receptor are positioned according to a defined relationship. Depending on the examination, the radiographer may need to:

• place the part parallel to the detector
• place the part perpendicular to the detector
• angle the detector
• angle the central ray
• use a combination of these approaches

The purpose is to obtain the required anatomical projection while minimising unwanted distortion.

3.19 Part Positioning

Positioning the specific anatomical part is often more important than simply positioning the patient. The radiographer should assess:

• rotation
• flexion
• extension
• abduction
• adduction
• internal/external rotation
• anatomical alignment
• relationship to the detector

For example, positioning requirements for the shoulder, wrist, knee and ankle are very different even when the patient is in the same general position.

3.20 Joint Positioning

When imaging joints, the radiographer should consider the intended anatomical relationship. Depending on the examination, this may involve:

• maintaining a joint in a neutral position
• flexion
• extension
• internal rotation
• external rotation
• weight-bearing
• stress positioning

The appropriate position should be based on the clinical question and established examination protocol.

3.21 Breathing Instructions

Breathing instructions are an important part of positioning for examinations influenced by respiratory movement. The patient may be asked to:

• suspend respiration
• inhale deeply
• hold inspiration
• hold expiration
• breathe normally
• breathe shallowly

The instruction must be clear and given at the appropriate stage of the examination. The patient's ability to follow instructions should always be considered.

3.22 Positioning and Patient Condition

Ideal textbook positioning is not always possible. The radiographer may need to modify positioning because of:

• trauma
• pain
• restricted mobility
• neurological impairment
• surgery
• fractures
• casts or splints
• obesity
• pregnancy
• paediatric age
• reduced consciousness
• life-support equipment
• lines, drains or tubes

Patient safety takes priority over achieving an ideal geometric position. When modification is required, the radiographer should select the safest practical alternative that still provides the necessary diagnostic information.

3.23 Immobilisation

Some patients cannot maintain the required position without assistance. Appropriate immobilisation or positioning aids may include:

• sponges
• supports
• straps
• sandbags
• radiolucent devices
• specialised paediatric immobilisation equipment

Immobilisation should:

• maintain the required position
• prevent unnecessary movement
• protect the patient
• avoid obscuring important anatomy
• comply with local policy

A person should not routinely be used to hold a patient when an appropriate alternative is available.

3.24 Side Markers and Anatomical Identification

Correct side identification is essential in radiography. An appropriate anatomical side marker should be placed so that:

• the side is clearly identified
• it does not obscure important anatomy
• it is visible on the final image
• it is positioned appropriately for the examination

Electronic markers should not be used to replace an appropriate physical marker where local policy or professional requirements require physical identification. Incorrect or missing side identification can create a significant clinical risk.

3.25 Collimation and Positioning

Positioning and collimation should be performed together. The field should be:

large enough to include the required anatomy but no larger than necessary.

Good positioning helps the radiographer identify the correct anatomical boundaries and therefore apply appropriate collimation. Poor positioning can result in:

• unnecessary exposure
• anatomy being excluded
• excessive field size
• increased scatter
• repeat imaging

3.26 Positioning and Image Reproducibility

Standardised positioning improves the ability to compare current images with:

• previous examinations
• follow-up studies
• images from other institutions
• serial examinations

Reproducibility is particularly important for:

• orthopaedic follow-up
• fracture assessment
• chest imaging
• spinal studies
• alignment and measurement examinations

Consistent positioning helps distinguish genuine anatomical change from differences caused by technique.

3.27 Positioning and Image Evaluation

Positioning does not end when the exposure is made. The resulting image should be assessed to determine whether:

• the required anatomy is included
• the intended projection has been achieved
• rotation is acceptable
• centring is appropriate
• positioning landmarks are satisfactory
• the required joint or anatomical relationship is demonstrated
• collimation is appropriate
• motion is acceptable
• the image is diagnostically useful

This assessment is an essential part of the radiographer's role.

3.28 Practical Positioning Sequence

A useful general sequence for routine positioning is:

1. Confirm the examination — Establish:

• correct patient
• correct examination
• relevant clinical information
• correct anatomical side

2. Assess the patient — Consider:

• mobility
• pain
• trauma
• ability to cooperate
• infection precautions
• lines and tubes
• weight-bearing ability

3. Select the detector — Choose:

• appropriate detector size
• orientation
• detector position

4. Position the patient — Establish:

• patient position
• anatomical position
• part position
• rotation
• flexion/extension
• required joint position

5. Align the tube — Set:

• SID
• central-ray position
• beam direction
• required angulation

6. Collimate — Restrict the field to the required anatomy.

7. Apply the appropriate breathing instruction — Where required, explain the instruction before exposure.

8. Check before exposure — Confirm:

• anatomy included
• correct side
• marker
• positioning
• centring
• collimation
• patient safety
• equipment clearance

9. Make the exposure — Use the appropriate technical factors for the examination and patient.

10. Evaluate the image — Confirm diagnostic acceptability before completing the examination whenever practical.

3.29 Projection Geometry

The appearance of anatomy on a radiograph depends on the relationship between:

X-ray source → patient anatomy → image receptor

Changes in this geometry can alter:

• magnification
• distortion
• superimposition
• spatial sharpness
• anatomical relationships

Understanding this relationship is essential when performing specialised projections.

3.30 Distortion and Positioning

Distortion occurs when the size or shape of anatomy on the image does not accurately represent its physical form. It may result from:

• incorrect central-ray angulation
• patient rotation
• increased OID
• inappropriate alignment
• incorrect detector positioning

Distortion is not always undesirable. Some specialised projections intentionally use controlled distortion to separate or demonstrate particular anatomical structures. The radiographer therefore needs to understand when distortion is unwanted and when it is an intentional part of the projection.

3.31 Weight-Bearing Positioning

Some examinations require the patient to bear weight. Examples include selected:

• foot examinations
• ankle examinations
• knee examinations
• lower-limb alignment studies
• spinal examinations

Weight-bearing imaging may demonstrate anatomical relationships that are not apparent when the patient is non-weight-bearing. Patient stability and safety must be assessed before weight-bearing imaging.

3.32 Stress and Functional Positioning

Certain examinations require the anatomy to be positioned under controlled stress or during a particular movement. These examinations may be used to assess:

• joint stability
• ligamentous injury
• alignment
• range of movement

Stress positioning should only be performed when clinically indicated and according to the appropriate protocol. The patient's condition and the potential for injury must be considered before applying stress.

3.33 Positioning in Trauma

Trauma imaging requires particular care because the ideal position may not be safe or possible. Important principles include:

• avoid unnecessary movement
• maintain immobilisation when indicated
• follow spinal precautions
• adapt projections to the patient's condition
• use horizontal-beam techniques when appropriate
• communicate with the trauma team
• prioritise patient stability over textbook positioning

The radiographer should obtain the required diagnostic information with the minimum necessary movement of the injured patient. Trauma positioning is covered in greater detail within the dedicated Trauma & Emergency Radiography section.

3.34 Positioning in Mobile Radiography

Mobile examinations frequently involve patients who cannot be transferred to a standard radiographic room. Positioning may therefore be affected by:

• bed position
• limited space
• monitoring equipment
• ventilators
• lines and tubes
• patient condition

The radiographer should adapt the examination while maintaining appropriate detector placement, central-ray alignment, collimation and radiation protection. Detailed mobile positioning principles are covered in the dedicated Mobile & Portable Radiography section.

3.35 Positioning Principles — Summary

Accurate positioning can be understood through five fundamental relationships:

Patient: Where and how is the patient positioned?

Part: How is the anatomical region aligned and rotated?

Detector: Where is the image receptor positioned relative to the anatomy?

Central Ray: Where is the beam centred and in which direction does it travel?

Geometry: What are the SID, OID, angulation and alignment relationships?

When these five elements are correctly coordinated, the probability of obtaining a diagnostic and reproducible image is greatly increased.

Key Learning Points

At the end of this topic, the learner should be able to:

1. Define the anatomical position.
2. Use standard anatomical directional terminology correctly.
3. Describe the sagittal, coronal and transverse planes.
4. Explain the principal body axes.
5. Describe common patient positions.
6. Distinguish between patient position and radiographic projection.
7. Define AP, PA, lateral, oblique and axial projections.
8. Explain the role of the central ray.
9. Explain the importance of accurate centring.
10. Identify the purpose of anatomical landmarks in positioning.
11. Explain how rotation affects radiographic appearance.
12. Position the detector appropriately for an examination.
13. Explain the relationship between SID, OID and image geometry.
14. Explain how beam divergence affects magnification and distortion.
15. Understand the effect of focal-spot size on geometric sharpness.
16. Apply appropriate positioning of joints and anatomical parts.
17. Give appropriate breathing instructions.
18. Select appropriate positioning or immobilisation aids.
19. Understand the importance of accurate side markers.
20. Apply appropriate collimation in conjunction with positioning.
21. Recognise when ideal positioning must be modified because of patient condition.
22. Understand positioning considerations in trauma and mobile radiography.
23. Evaluate whether positioning has produced a diagnostically acceptable image.
24. Apply positioning principles consistently to produce reproducible examinations.

Radiographic Image Quality

1. Contrast

1.1 Definition

Radiographic contrast describes the difference in signal or optical appearance between adjacent areas of a radiographic image. In practical terms, contrast determines how readily one anatomical structure can be distinguished from another.

A high-contrast image contains relatively pronounced differences between adjacent structures, whereas a low-contrast image contains more gradual differences. Contrast is particularly important when the clinical task requires differentiation of structures with relatively similar X-ray attenuation.

1.2 Subject Contrast

Subject contrast originates primarily from differences in X-ray attenuation between tissues and structures within the patient. It is influenced by:

• Tissue composition
• Tissue thickness
• Physical density
• Atomic number
• Effective X-ray energy
• Pathological changes
• Presence of contrast media

For example, bone and soft tissue have substantially different attenuation characteristics, producing strong subject contrast. In contrast, many soft tissues have relatively similar attenuation and therefore produce more subtle differences.

1.3 Effect of kVp on Contrast

Tube potential is an important determinant of the X-ray beam's energy distribution and therefore influences subject contrast.

In general:

• Lower kVp tends to produce greater subject contrast.
• Higher kVp tends to produce lower subject contrast and greater penetration.
• Increasing kVp generally increases X-ray output as well as beam energy.
• The appropriate kVp depends on the body part, patient size, detector system and diagnostic task.

The traditional description of low kVp = high contrast and high kVp = low contrast remains useful for understanding radiographic physics, but it should not be interpreted as an absolute rule for modern digital imaging. Digital image processing can substantially modify the displayed appearance of contrast. Consequently, the displayed image may not directly reflect the original subject contrast produced during exposure.

1.4 Patient Thickness and Contrast

Patient thickness affects the amount and distribution of radiation reaching the detector. As thickness increases:

• More photons are attenuated.
• More scattered radiation may be generated.
• Detector exposure may decrease if technique is not adjusted.
• Image noise may increase.
• Contrast may be affected by changes in beam penetration and scatter.

Technique selection should therefore account for patient size rather than relying on a single exposure setting for every patient.

1.5 Scatter Radiation and Contrast

Scatter radiation is an important cause of unwanted image signal. Scatter reaching the detector can:

• Add unwanted exposure across the image.
• Reduce visible subject contrast.
• Obscure subtle anatomical differences.
• Make the image appear more uniform or "fogged."

Scatter becomes particularly important with:

• Increased patient thickness
• Larger irradiated fields
• Higher-energy techniques
• Poor collimation

Scatter can be reduced through appropriate:

• Collimation
• Patient positioning
• Grid use where appropriate
• Air-gap techniques in selected examinations
• Exposure optimisation

Collimation is one of the most important practical methods of controlling scatter production.

1.6 Digital Image Processing and Display Contrast

In digital radiography, the displayed image can be processed to modify brightness, contrast and other characteristics. This creates an important distinction between:

Subject contrast → detector signal → image processing → displayed image

Digital processing can improve the visual presentation of anatomy, but it cannot recover anatomical information that was never adequately recorded. For example, excessive exposure may still produce an apparently acceptable image because digital systems can compensate for changes in detector exposure. This does not mean that the exposure was appropriate.

2. Spatial Resolution

2.1 Definition

Spatial resolution is the ability of an imaging system to distinguish small structures or two closely positioned objects as separate entities. It is often described in terms of line pairs per millimetre or through other resolution-testing methods. High spatial resolution allows fine anatomical structures and small details to be visualised more clearly.

2.2 Factors Affecting Spatial Resolution

Spatial resolution is influenced by several components of the imaging chain:

• Focal spot size
• Object-to-image receptor distance (OID)
• Source-to-image receptor distance (SID)
• Detector characteristics
• Pixel size and sampling
• Image processing
• Patient motion
• Equipment performance

2.3 Focal Spot Size

A smaller focal spot generally produces better geometric sharpness because it reduces the size of the penumbra. However, small focal spots cannot tolerate the same tube loading as larger focal spots.

Therefore:

Small focal spot → improved spatial resolution → lower heat tolerance

Large focal spot → greater tube loading capability → greater geometric unsharpness

The focal spot should therefore be selected according to the examination and exposure requirements rather than simply choosing the smallest available focal spot.

2.4 Object-to-Image Receptor Distance

OID has a major influence on geometric magnification and unsharpness. As OID increases:

• Magnification increases.
• Geometric unsharpness increases.
• Recorded detail may decrease.

Where clinically and practically possible, the anatomy should be positioned close to the detector. This is particularly important when imaging small structures requiring high spatial detail.

2.5 Source-to-Image Receptor Distance

Increasing SID generally reduces magnification and can improve geometric accuracy. A longer SID also reduces the relative effect of focal-spot penumbra for a given OID. The relationship between SID and OID should therefore always be considered together rather than independently.

2.6 Detector Characteristics

Detector design has an important influence on recorded spatial detail. Relevant characteristics include:

• Pixel size
• Detector element dimensions
• Sampling frequency
• Detector construction
• Modulation transfer characteristics
• Electronic performance
• Image processing

A detector with smaller effective sampling dimensions can potentially record finer detail, but spatial resolution is determined by the performance of the complete imaging system rather than pixel size alone.

3. Noise

3.1 Definition

Image noise is unwanted random variation in image signal that can interfere with the visibility of anatomical structures. Noise becomes particularly important when attempting to visualise low-contrast structures. The most important source of noise in conventional X-ray imaging is quantum noise, also called quantum mottle.

3.2 Quantum Noise

Quantum noise occurs because X-ray photons arrive at the detector in a statistically random manner. When relatively few photons are detected, the statistical variation becomes more noticeable.

Therefore:

Fewer detected photons → greater relative noise

More detected photons → lower relative noise

This relationship is important because increasing exposure can reduce quantum noise, but doing so also increases radiation dose.

3.3 Factors Affecting Quantum Noise

Quantum noise is influenced by:

• mAs
• kVp
• Patient thickness
• Beam filtration
• Detector efficiency
• Grid use
• Collimation
• Patient attenuation

If too few photons reach the detector, the resulting image may contain increased noise and reduced visibility of subtle structures.

3.4 Noise and Radiation Dose

A fundamental principle in digital radiography is that acceptable image quality should not be achieved simply by increasing exposure unnecessarily.

Modern detectors have a relatively wide exposure latitude. This means that an image can sometimes appear visually acceptable despite excessive detector exposure. This creates the potential for dose creep, where exposure factors gradually increase over time without an obvious deterioration in displayed image appearance.

Exposure indicators and local technique charts should therefore be used alongside clinical image evaluation.

3.5 Signal-to-Noise Ratio

The signal-to-noise ratio (SNR) describes the strength of useful image information relative to random noise. Higher SNR generally improves the ability to distinguish anatomical information from background variation.

SNR is influenced by:

• Number of detected photons
• Detector efficiency
• Exposure
• Reconstruction or processing methods
• Patient attenuation

The objective is not to eliminate noise completely but to achieve an appropriate level of image quality for the clinical task while keeping radiation exposure as low as reasonably achievable.

4. Distortion

4.1 Definition

Distortion occurs when the recorded size or shape of an anatomical structure differs from its true size or shape. Distortion is primarily a consequence of the three-dimensional anatomy being represented on a two-dimensional detector. It can be divided broadly into:

• Size distortion
• Shape distortion

4.2 Size Distortion

Size distortion refers to magnification of the recorded anatomy. Magnification increases when:

• OID increases
• SID decreases

It can be expressed as:

Magnification factor (MF) = SID / SOD

where:

• SID = source-to-image receptor distance
• SOD = source-to-object distance

Because:

SOD = SID − OID

magnification can also be understood as increasing when the object moves farther away from the detector or closer to the X-ray source.

4.3 Shape Distortion

Shape distortion occurs when the recorded shape of anatomy is altered. It may result from:

• Object misalignment
• Detector misalignment
• Incorrect central-ray angulation
• Anatomical rotation
• Incorrect positioning

Two common forms are:

Foreshortening: The recorded structure appears shorter than its true length. This can occur when the anatomy is not appropriately aligned with the detector and central ray.

Elongation: The recorded structure appears longer than its true length. This may occur when the relative alignment of the anatomy, detector and central ray produces an increased projected length.

4.4 Controlling Distortion

Distortion can be reduced by appropriate geometric alignment. Important principles include:

• Keep the anatomy close to the detector where appropriate.
• Use an appropriate SID.
• Align the anatomy correctly.
• Align the detector with the anatomical region of interest.
• Use the appropriate central-ray direction and angulation.
• Avoid unnecessary rotation.
• Follow examination-specific positioning requirements.

Some examinations deliberately use controlled magnification or distortion because the projection is designed to demonstrate a particular anatomical relationship. Therefore, distortion is not always an error; it becomes problematic when it is unintended or clinically misleading.

5. Motion

5.1 Definition

Motion produces image unsharpness when the patient, anatomical structure, detector or equipment moves during the exposure. Motion can significantly reduce the visibility of fine anatomical detail.

It is particularly important in:

• Chest radiography
• Abdominal radiography
• Paediatric imaging
• Trauma imaging
• Imaging of patients who cannot cooperate
• Examinations requiring longer exposure times

5.2 Types of Motion

Motion may be:

Voluntary Motion: Movement that the patient can consciously control, such as:

• Changing position
• Moving an extremity
• Breathing during an exposure

Involuntary Motion: Movement that the patient cannot easily control, such as:

• Tremor
• Muscle spasm
• Cardiac motion
• Peristalsis
• Respiratory movement

5.3 Reducing Motion

Motion can be minimised through:

• Clear explanation of the examination
• Appropriate patient preparation
• Comfortable positioning
• Immobilisation where necessary
• Short exposure time
• Appropriate tube current
• Clear breathing instructions
• Adequate communication
• Appropriate use of equipment supports

The radiographer should identify the likely source of movement before exposure and modify the examination accordingly.

6. Image Sharpness and Unsharpness

Image sharpness refers to how clearly boundaries and fine structures are reproduced. Image unsharpness can arise from several sources.

Geometric unsharpness — Associated with:

• Focal spot size
• OID
• SID

Motion unsharpness — Caused by movement during exposure.

Detector-related unsharpness — Associated with:

• Detector design
• Sampling characteristics
• Pixel dimensions
• Detector performance
• Image processing

Total image sharpness is therefore a combined property of the X-ray tube, geometry, detector, patient and exposure technique.

7. Image Artefacts

7.1 Definition

An artefact is a structure, appearance or signal on an image that does not represent the patient's actual anatomy or pathology. Artefacts can originate from:

• Patient-related factors
• Equipment
• Detector
• Exposure technique
• Processing
• Foreign objects
• Environmental factors

Examples include:

• Clothing
• Jewellery
• Buttons and zips
• Patient monitoring equipment
• Detector defects
• Grid-related artefacts
• Processing errors
• Motion
• Foreign material
• Image stitching errors

Artefacts can obscure anatomy and may sometimes mimic pathology.

7.2 Managing Artefacts

The radiographer should:

1. Identify the artefact.
2. Determine its likely source.
3. Decide whether it affects diagnostic interpretation.
4. Correct the cause where possible.
5. Repeat the examination only when clinically justified.

Repeated imaging should not be performed simply because an image is aesthetically imperfect if the diagnostic objective has already been achieved.

8. Exposure Adequacy in Digital Radiography

In film-screen imaging, optical density was strongly related to exposure. Digital systems behave differently.

A digital image may have an apparently appropriate brightness over a relatively wide range of detector exposures because image processing modifies the displayed image. This means that image brightness alone is not a reliable indicator of whether the exposure was appropriate.

Radiographers should consider:

• Exposure indicator
• Deviation from recommended technique
• Image noise
• Anatomical penetration
• Clinical task
• Positioning
• Collimation
• Repeat analysis
• Local exposure protocols

The exposure indicator should be interpreted according to the specific manufacturer's system because terminology and numerical scales differ between manufacturers.

9. Image Quality and Clinical Acceptability

A technically good image is not necessarily the image with the highest possible spatial resolution or the lowest possible noise. The most important question is:

Does the image contain sufficient information to answer the clinical question safely and reliably?

Diagnostic acceptability depends on:

• Correct anatomy included
• Appropriate positioning
• Adequate penetration
• Appropriate contrast
• Sufficient spatial detail
• Acceptable noise
• Minimal motion
• Appropriate collimation
• Correct side marker
• Absence of significant artefacts
• Appropriate exposure
• Relevant pathology not obscured

Image evaluation should therefore be linked to the clinical purpose of the examination.

10. Relationship Between Image Quality Factors

The major image-quality characteristics should not be considered in isolation.

These factors interact continuously during an examination. For example:

Increasing mAs → increases detected photons → reduces quantum noise → but increases radiation exposure.

Reducing exposure time → reduces the opportunity for motion → but may require higher tube current.

Increasing SID → reduces magnification → changes detector exposure because of beam intensity differences → may require technique adjustment.

Increasing OID → increases magnification → increases geometric unsharpness.

Understanding these relationships allows the radiographer to optimise the examination rather than adjusting individual factors in isolation.

11. Image Quality Optimisation

The objective of optimisation is to obtain an image that is fit for the intended diagnostic purpose with the minimum reasonable radiation exposure.

Practical optimisation includes:

Patient positioning: Accurate positioning reduces distortion and prevents unnecessary repeat examinations.

Appropriate exposure selection: Select kVp and mAs according to patient size, examination requirements and local technique charts.

Scatter control: Use appropriate collimation and grids where clinically indicated.

Geometric optimisation: Use suitable SID, minimise unnecessary OID and select an appropriate focal spot.

Motion control: Use appropriate exposure times, immobilisation and breathing instructions.

Detector optimisation: Use the correct detector, positioning and exposure range.

Digital processing: Ensure appropriate processing and display without relying on post-processing to compensate for poor acquisition.

Repeat reduction: Analyse rejected or repeated examinations to identify avoidable causes.

Dose awareness: Avoid unnecessarily high detector exposure even when the displayed image appears acceptable.

12. Diagnostic Task and Image Quality

Different examinations require different balances between image-quality characteristics. For example:

• A skeletal examination may require high spatial detail.
• A chest examination requires adequate visualisation of both lung fields and mediastinal structures across a wide range of tissue attenuation.
• An abdominal examination may require adequate penetration and acceptable noise.
• A paediatric examination requires particular attention to dose optimisation and repeat avoidance.
• Trauma imaging may require accepting a less-than-ideal position when moving the patient could cause harm.

Therefore, there is no single universal definition of the "best" radiograph. The appropriate image is the one that provides sufficient diagnostic information for the clinical question while maintaining patient safety and dose optimisation.

13. Practical Image Quality Evaluation

Before accepting an image, the radiographer should consider:

Anatomy:

• Is the required anatomy included?
• Is the clinically relevant region adequately demonstrated?

Positioning:

• Is the patient correctly positioned?
• Is there unwanted rotation?
• Is the anatomical region correctly aligned?

Exposure:

• Is penetration appropriate?
• Is there excessive or insufficient noise?
• Is the detector exposure appropriate?

Contrast:

• Are relevant anatomical structures distinguishable?
• Has scatter reduced useful contrast?

Spatial detail:

• Are fine structures adequately demonstrated?
• Is geometric sharpness acceptable?

Motion:

• Is there evidence of respiratory, voluntary or involuntary movement?

Distortion:

• Is magnification expected and appropriate?
• Is there unintended shape distortion?

Collimation:

• Is the field appropriately restricted?
• Is unnecessary anatomy or irradiated tissue included?

Marker:

• Is the correct anatomical side marker visible?
• Is it positioned so that it does not obscure important anatomy?

Artefacts:

• Are there any artefacts that could affect interpretation?

Diagnostic acceptability:

• Can the image answer the clinical question?
• Would repeating the image provide a meaningful diagnostic improvement?

14. Common Causes of Poor Image Quality

15. Key Learning Points

• Image quality is produced by the interaction of exposure, geometry, patient factors, detector performance and image processing.
• Contrast describes differences between adjacent image regions.
• Subject contrast is influenced by tissue characteristics and X-ray beam energy.
• Scatter reduces useful contrast and can be controlled through appropriate collimation and other techniques.
• Spatial resolution describes the ability to distinguish small or closely spaced structures.
• Small focal spots generally improve geometric sharpness but have lower heat-loading capability.
• Increased OID increases magnification and geometric unsharpness.
• Quantum noise is strongly related to the number of X-ray photons detected.
• Increasing exposure can reduce quantum noise but increases radiation dose.
• Distortion may involve changes in recorded size or shape.
• Correct alignment of the patient, detector and central ray helps control unintended distortion.
• Motion is an important cause of image unsharpness.
• Digital image brightness should not be used alone to judge exposure adequacy.
• Exposure indicators should be interpreted according to the specific digital imaging system.
• Artefacts can obscure anatomy or mimic pathology.
• The goal is not maximum image quality at any dose; it is diagnostically sufficient image quality with appropriate dose optimisation.
• Image evaluation should always consider the clinical question.

Digital Radiography

5.1 CR and DR

Digital radiography encompasses two main technologies: computed radiography (CR) and direct digital radiography (DR). Both produce digital images, but they differ in detector technology, workflow and performance characteristics.

Computed Radiography (CR)

CR uses photostimulable phosphor (PSP) imaging plates housed in cassettes that are broadly similar in size and handling to conventional film-screen cassettes. When the imaging plate is exposed to X-rays, the phosphor absorbs energy and stores a latent image in the form of trapped electrons within the phosphor lattice.

The cassette is then taken to a CR reader, where the imaging plate is removed and scanned with a finely focused laser. The laser stimulates the trapped electrons, causing them to release their stored energy as light — a process called photostimulated luminescence. The emitted light is collected by a photomultiplier tube and converted into an electronic signal, which is then digitised to produce the digital image. After reading, the plate is exposed to intense light to erase any residual stored energy, making it ready for reuse.

Advantages of CR include compatibility with existing X-ray equipment designed for cassette-based workflows, portability, and the ability to use cassettes in positions where a fixed DR detector cannot be placed. Disadvantages include a slower workflow due to the separate reading step, lower detector efficiency compared with many DR systems, and susceptibility to specific artefacts such as scatter within the phosphor, plate handling damage and reader-related issues.

Typical CR artefacts include scratches or pressure marks on the imaging plate, dust or contamination on the plate surface, ghost images from incomplete erasure, laser scanning artefacts, and plate fog from background radiation or improper storage.

Digital Radiography (DR)

DR systems use flat-panel detectors that acquire images directly into the digital imaging system without the need for a separate reading step. The detector is permanently or semi-permanently integrated into the X-ray system or used as a wireless portable detector, and the image appears on the workstation within seconds of exposure.

DR detectors operate using one of two conversion methods:

Direct conversion uses a photoconductor, typically amorphous selenium, which converts incoming X-ray photons directly into electrical charge. Because there is no intermediate light-conversion step, the charge pattern closely follows the original X-ray pattern, which helps preserve spatial resolution.

Indirect conversion uses a scintillator — commonly caesium iodide or gadolinium oxysulphide — to convert X-ray photons into light. The light is then detected by a photodiode array, typically based on amorphous silicon, which converts the light into electrical charge. The intermediate light-conversion step can introduce some lateral spread of signal, which may slightly reduce spatial resolution compared with direct conversion, though modern indirect detectors achieve excellent clinical performance.

In both types, the charge pattern is read out by a thin-film transistor (TFT) array, which transfers the electrical signal from each detector element to the system electronics for digitisation and processing.

Detector efficiency — the ability to absorb X-ray photons and convert them into usable signal — varies between detector types and materials. Higher detector efficiency generally means that less patient exposure is needed to produce a diagnostically adequate image, though the relationship between detector efficiency and patient dose also depends on technique selection, clinical task and optimisation.

CR vs DR Comparison

It should not be assumed that DR is automatically lower dose than CR. Patient dose depends on detector performance, technique selection, the clinical task and optimisation practice. A well-optimised CR system can achieve appropriate imaging at reasonable dose, and a poorly optimised DR system can still deliver excessive exposure.

5.2 Digital Image Acquisition

The complete digital image acquisition pathway can be summarised as:

X-ray production → patient → detector → signal generation → analogue-to-digital conversion → image processing → image display → storage / PACS

When an X-ray exposure is made, the beam is produced by the X-ray tube and directed towards the patient. As the beam passes through the body, some photons are absorbed, some are scattered and some pass through to form the remnant beam. The remnant beam carries the pattern of differential attenuation that contains the diagnostic information.

The remnant beam reaches the digital detector, which responds to the incoming X-ray photons by producing an electrical signal proportional to the amount of radiation received. In CR, this response is stored as trapped electrons in the phosphor and read later. In DR, the response is read immediately by the detector electronics.

The analogue electrical signal from the detector is converted into a digital signal by an analogue-to-digital converter (ADC). The ADC samples the continuous signal at discrete intervals and assigns a numerical value to each sample. These numerical values are called pixel values, and they represent the intensity of radiation detected at each point on the detector.

The digital image is composed of a matrix of pixels arranged in rows and columns. Each pixel corresponds to a small area of the detector surface. Pixel size — the physical dimensions of each detector element — influences the spatial resolution of the system: smaller pixels generally allow finer detail to be resolved, though resolution also depends on the focal spot, geometry and sampling process.

Bit depth determines the number of possible grey levels that can be assigned to each pixel. A greater bit depth allows a wider range of signal values to be represented, which supports smoother gradation and more flexible post-processing.

Dynamic range refers to the range of detector exposures over which the detector produces a usable signal. Digital detectors generally have a wide dynamic range, meaning they can produce useful images across a broad range of exposures. This is one of the key advantages of digital radiography over film-screen systems.

Detective Quantum Efficiency (DQE) describes how efficiently a detector converts the incoming X-ray information into a useful output signal. A higher DQE means that more of the incoming photon information contributes to the final image, which can permit lower patient exposure for a given image quality. DQE values vary between detector types and energies and should not be treated as a single universal number.

5.3 Digital Image Formation and Processing

Raw detector information is not directly suitable for clinical interpretation. It must undergo a series of processing steps to become a clinically usable image.

Pre-processing

Before the image data can be used, the detector output is corrected for known systematic variations:

• Detector calibration: The detector is calibrated to ensure consistent response across all detector elements.
• Offset correction: Removes the baseline electronic signal present even when no radiation reaches the detector (dark current).
• Gain correction: Compensates for variations in sensitivity between individual detector elements.
• Bad or dead pixel correction: Identifies non-functional detector elements and interpolates their values from neighbouring pixels.
• Detector uniformity correction: Ensures a uniform response across the entire detector surface.

These corrections are typically performed automatically by the imaging system and are fundamental to producing a consistent, artefact-free image.

Image Recognition

After pre-processing, the system identifies the exposed region of the detector. This involves:

• Exposure-field recognition: The system identifies the boundaries of the collimated field to determine which portion of the detector contains useful image data.
• Histogram analysis: The system analyses the distribution of pixel values within the exposed field to identify the relevant anatomical data and determine appropriate processing parameters.

Appropriate collimation is essential for correct image recognition. If the field is too large or poorly collimated, the histogram may include non-anatomical regions, which can cause processing errors and incorrect image appearance.

Image Processing

Once the exposed field and histogram have been analysed, the system applies processing to convert the corrected raw data into a clinically useful image. Common processing functions include:

• Rescaling: Adjusts the overall brightness of the displayed image to a consistent level regardless of the exposure received.
• Look-Up Tables (LUTs): Map raw pixel values to displayed grey levels according to a predefined curve, controlling the overall tone and contrast of the image.
• Window width and window level: Control the range and centre of grey levels displayed, allowing the viewer to emphasise different tissue types.
• Contrast adjustment: Modifies the difference between adjacent structures in the displayed image.
• Edge enhancement: Accentuates boundaries between structures to improve perceived sharpness.
• Noise reduction: Applies smoothing or filtering algorithms to reduce visible noise.
• Image smoothing: Reduces high-frequency information to produce a less noisy appearance.

Post-processing can change image appearance significantly, but it cannot recover information that was never acquired. If anatomy was not adequately positioned, if exposure was insufficient, or if motion occurred during the exposure, no amount of processing can fully correct the deficiency.

Excessive processing may:

• Hide pathology by over-smoothing or altering contrast.
• Create artificial edges that do not correspond to real anatomical structures.
• Increase apparent noise by over-enhancing high-frequency information.
• Reduce diagnostic reliability by producing an image that looks processed rather than accurate.

Processing must support, not replace, appropriate positioning and exposure.

5.4 Exposure Latitude and Dynamic Range

Exposure latitude refers to the range of detector exposures over which a clinically acceptable image can be produced. Film-screen systems had a relatively narrow exposure latitude: underexposure produced a too-light image and overexposure produced a too-dark image, and both were often clinically unusable.

Digital systems generally have a much wider useful exposure range. Because the detector has a broad dynamic range and the image is processed to a consistent brightness, a digital image can appear visually acceptable even when the detector has received significantly more or less radiation than the target exposure.

This is both an advantage and a risk. The advantage is that digital systems are more forgiving of minor exposure variations, reducing the need for repeats due to exposure error. The risk is that image brightness alone is not a reliable indicator of patient exposure. An image that looks well-exposed on the monitor may have been produced with an unnecessarily high exposure, and the patient received more radiation than was needed.

The relationship between detector exposure and image noise is important. When detector exposure is low, quantum noise increases because fewer photons contribute to the image, and the image may appear grainy. When detector exposure is high, noise decreases, but the patient receives more radiation than necessary. The goal is to find the exposure that provides adequate image quality for the clinical task without unnecessary dose.

A good-looking digital image does not automatically mean the exposure was appropriate. Exposure indicators and technique optimisation are essential to ensure that image appearance and patient exposure are both managed correctly.

5.5 Exposure Indicators

Exposure indicators provide information about the amount of radiation received by the detector during an exposure. They are a key tool for monitoring and optimising technique in digital radiography.

Important concepts:

• Detector exposure versus patient dose: An exposure indicator reflects the radiation reaching the detector, not the radiation absorbed by the patient. Patient dose depends on many factors including patient thickness, field size, kVp, mAs, grid use and filtration. The exposure indicator should not be treated as a direct measurement of patient absorbed dose.
• Exposure Index (EI): A numerical value that indicates the level of detector exposure. The exact calculation and terminology vary between manufacturers.
• Deviation Index (DI): A standardised measure that indicates how far the actual exposure deviates from a target exposure. Where supported, a DI of zero indicates that the exposure matched the target. Positive values indicate overexposure and negative values indicate underexposure. The DI is intended to provide a more universally comparable metric, but its implementation may still vary between systems.
• Target exposure: The detector exposure that the system or department considers appropriate for a given examination and patient size. Target values are equipment-specific and should be established according to manufacturer guidance and local protocol.
• Manufacturer-specific indicators: Different manufacturers use different names, scales and calculation methods for exposure indicators. Numerical values from one system are not directly comparable with values from another system.

Exposure indicators should be interpreted alongside the clinical image, not in isolation. An exposure indicator within the target range does not guarantee that the image is diagnostically adequate, and an indicator outside the range does not always mean the image must be repeated. The radiographer must use professional judgement to evaluate both the indicator and the image quality together.

Limitations of exposure indicators include:

• They reflect detector exposure, not patient dose.
• They may be affected by collimation, positioning and the presence of metal or prostheses.
• They may not account for patient size or composition accurately.
• They are equipment-specific and not universally interchangeable.

Exposure information should be recorded in the imaging record and DICOM metadata where applicable, so that dose monitoring and repeat/reject analysis can be performed. Requirements and implementation may vary according to local regulations, equipment specifications and departmental protocols.

Users must follow manufacturer guidance, equipment-specific specifications, local departmental protocols and applicable national or international standards for exposure indicator interpretation.

5.6 Exposure Creep

Exposure creep is the gradual increase in exposure factors over time that can occur in digital radiography without being immediately obvious. Because digital systems have a wide exposure latitude, images produced with higher-than-necessary exposure can still look acceptable on the monitor. The processing adjusts the brightness and contrast to a consistent appearance, masking the fact that the detector received more radiation than needed.

Several factors contribute to exposure creep:

• Wide exposure latitude conceals overexposure — the image does not look too dark, as it would with film.
• Higher exposure produces lower noise, which may be visually preferred even when the lower-noise image is not clinically necessary.
• Technique charts may not be updated when equipment or detectors change.
• Radiographers may gradually increase exposure factors to reduce repeat rates without realising the cumulative effect on patient dose.
• Exposure indicators may not be routinely monitored.

Consistently low image noise can sometimes indicate unnecessarily high exposure. While low noise is desirable, there is a point beyond which further noise reduction provides no additional diagnostic value but increases patient dose.

Preventing exposure creep requires:

• Routine monitoring of exposure indicators against target ranges.
• Use and regular review of equipment-specific technique charts.
• Repeat and reject analysis to identify systematic overexposure.
• Departmental dose monitoring and comparison with diagnostic reference levels (DRLs).
• Radiographer awareness and professional judgement.

Digital image quality should not be improved simply by increasing exposure when the existing image is already diagnostically adequate.

5.7 Automatic Exposure Control in DR

Automatic exposure control (AEC) is a system that terminates the X-ray exposure once a predetermined amount of radiation has been detected, helping to achieve appropriate detector exposure without manual mAs calculation. In digital radiography, AEC remains a valuable tool, but it must be used correctly to be effective.

AEC typically uses ionisation chambers positioned behind the patient and in front of the detector. When the selected chamber receives the target amount of radiation, the AEC sends a signal to terminate the exposure. Some DR systems also offer detector-based AEC, which uses the digital detector itself to monitor exposure and terminate the generator.

Key considerations for AEC use in digital radiography:

• Chamber selection: The correct chamber or combination of chambers must be selected for the examination. Incorrect selection can lead to overexposure or underexposure.
• Patient positioning over the chamber: The anatomical region of interest must be correctly centred over the selected chamber. If the chamber is positioned under a different thickness or density than intended, the AEC will terminate the exposure at the wrong point.
• Backup timer or backup mAs: A backup timer or backup mAs limit should always be set to prevent excessively long exposures if the AEC fails to terminate correctly.
• Prostheses, metal and other objects: Metal implants, prostheses or other high-density objects over the AEC chamber can attenuate the beam and cause the AEC to extend the exposure, potentially overexposing other regions.
• Patient habitus: Very large or very small patients may challenge AEC accuracy. Technique charts and AEC settings should be appropriate for the patient size range typically encountered.
• Pathology: Significant pathology (such as a large effusion, consolidation or pneumothorax) can alter attenuation and affect AEC behaviour.
• Centring and collimation: Correct centring and collimation are essential because the AEC responds to whatever radiation reaches the chamber. Poor collimation that allows scatter to reach the chamber can cause premature exposure termination.

The relationship between AEC, technique charts, patient size, detector exposure, exposure indicators, image quality and patient dose is interconnected. AEC helps achieve appropriate detector exposure but does not replace the need for correct positioning, appropriate technique selection and image evaluation.

Common AEC errors include:

• Selecting the wrong chamber for the examination.
• Centring the patient incorrectly so the chamber is not under the intended anatomy.
• Failing to set a backup timer, risking excessive exposure if the AEC malfunctions.
• Using AEC for examinations or patient positions where it is not appropriate.
• Not adjusting technique for very large or very small patients.
• Placing metal or other dense objects over the AEC chamber.

5.8 Digital Image Quality

The principles of radiographic image quality discussed in the Radiographic Image Quality section apply fully to digital radiography. Here, these principles are applied specifically to the digital context.

Contrast

Subject contrast is determined by the differential attenuation of X-rays by different tissues and is influenced by kVp, patient thickness and composition. Digital display contrast is controlled by processing — window width, window level, LUTs and contrast adjustment algorithms. Scatter reduces subject contrast before it reaches the detector, and grids or collimation can help manage scatter. Processing can enhance displayed contrast but cannot restore subject contrast that was lost due to excessive scatter or inappropriate kVp.

Spatial Resolution

Spatial resolution in digital radiography is influenced by pixel size, the sampling process, detector characteristics, focal spot size, SID and OID. Smaller pixels and smaller focal spots generally support finer resolution. Greater SID and reduced OID improve geometric resolution. However, the detector's pixel size places a fundamental limit on the maximum resolution the system can achieve, regardless of geometry.

Noise

Noise in digital radiography includes quantum noise (statistical variation in photon arrival), detector electronic noise, and noise introduced or amplified by processing. Quantum noise is strongly influenced by the number of photons reaching the detector: lower exposure means fewer photons and more visible noise. The signal-to-noise ratio (SNR) describes the relationship between useful signal and noise. Higher SNR generally means a cleaner image, but achieving it by increasing exposure increases patient dose. The goal is adequate SNR for the clinical task, not the highest possible SNR.

Sharpness

Sharpness is influenced by motion unsharpness, geometric unsharpness (focal spot, OID, SID) and detector limitations. Motion can be reduced by using shorter exposure times, clear breathing instructions and appropriate immobilisation. Geometric unsharpness can be reduced by using a smaller focal spot, minimising OID and maximising SID where practical. Detector sharpness is limited by pixel size and sampling.

Distortion

Distortion in digital radiography results from magnification and shape distortion caused by OID, SID, beam angulation and positioning. Correct alignment of patient, part, detector and central ray is essential to minimise unwanted distortion. The principles are the same as those discussed in the Radiographic Positioning Principles and Radiographic Image Quality sections.

Digital processing can modify image appearance, but it cannot replace accurate acquisition.

5.9 Digital Artefacts

Artefacts are unwanted features in the image that do not correspond to the patient's anatomy. Recognising, investigating and preventing artefacts is an essential radiography skill.

Detector-Related Artefacts

• Dead pixels: Individual detector elements that do not function, appearing as bright or dark dots. Usually corrected by interpolation but may become visible if numerous.
• Pixel defects: Detector elements that produce incorrect values consistently.
• Detector damage: Physical damage from impact, dropping or pressure, producing streaks, bands or non-uniform regions.
• Non-uniform detector response: Variations across the detector surface, often caused by calibration issues or detector ageing.
• Calibration problems: Incorrect or outdated calibration leading to shading, banding or inconsistent image appearance.
• Detector contamination: Dust, dirt or other contamination on the detector surface appearing as artefactual shadows.

Acquisition Artefacts

• Motion: Blurring from patient movement during exposure.
• Incorrect centring: The anatomy of interest not properly positioned over the detector, leading to missed anatomy or processing errors.
• Incorrect exposure field: The collimated field not matching the required anatomy, causing histogram analysis errors.
• Poor collimation: Excessive field size increasing scatter and potentially affecting processing.
• Grid-related artefacts: Grid lines, grid cut-off or moiré patterns from incorrect grid alignment or grid frequency interactions.
• Detector saturation: Occurs when the detector receives more radiation than it can measure, resulting in loss of information in the overexposed region.

Processing Artefacts

• Incorrect examination or view selection: Applying the wrong processing algorithm, producing inappropriate contrast or edge enhancement.
• Histogram analysis errors: The system misidentifies the exposure field or anatomical data, leading to incorrect rescaling and brightness.
• Incorrect processing algorithm: The algorithm does not match the examination, producing an unnatural appearance.
• Inappropriate edge enhancement: Over-enhancement creating artificial lines or increasing noise.
• Incorrect windowing: Default window settings not appropriate for the examination.

Equipment and Workflow Artefacts

• Foreign objects: Clothing, jewellery, buttons, hair clips or other items left in the field.
• Immobilisation devices: Radiopaque positioning aids or sandbags appearing on the image.
• Leads, tubes and lines: Monitoring equipment, IV lines or drains projected over anatomy.
• CR cassette and reader problems: Scratched or damaged imaging plates, incomplete erasure, dust on the plate, or reader laser scanning faults.

Artefact Reference Table

Radiographers should investigate any unexpected artefact rather than simply repeating the image. If the artefact is caused by a detector or equipment problem, repeating the image will reproduce the same artefact and add unnecessary patient dose. Persistent or unexplained artefacts should be reported for technical investigation.

5.10 Image Display and Post-Processing

After acquisition and processing, the digital image is displayed on a monitor for evaluation and interpretation. The acquisition workstation provides tools for adjusting the displayed image:

• Window width: Controls the range of grey levels displayed, affecting contrast.
• Window level: Controls the centre of the grey scale, affecting brightness.
• Zoom: Magnifies a region of the image for closer inspection.
• Pan: Moves the displayed image to view different regions.
• Magnification: Enlarges the image for detail viewing.
• Image rotation: Rotates the displayed image for orientation.
• Image annotation: Adds text, markers or measurements to the image.
• Edge enhancement: Adjusts sharpness of displayed edges.
• Noise reduction: Applies smoothing to reduce visible noise.
• Cropping: Removes unwanted portions of the displayed image.
• Electronic collimation: Applies a digital mask to hide anatomy outside the region of interest.

A critical distinction must be made between pre-exposure physical collimation and post-processing electronic cropping:

Physical collimation is performed before the X-ray exposure using the collimator. It restricts the X-ray field to the required anatomy, reducing irradiated tissue volume, scatter production and patient dose. Physical collimation is a radiation protection measure and an image quality measure.

Electronic cropping is applied after the exposure. It hides anatomy from the displayed image but does not remove the radiation that was already delivered to the patient. The tissue outside the digitally cropped region was still irradiated.

Electronic cropping must never be used as a substitute for proper radiation field collimation.

Display considerations include:

• Display quality: Diagnostic displays should meet appropriate standards for resolution, contrast and luminance.
• Calibration: Displays should be calibrated to standards such as DICOM Grayscale Standard Display Function (GSDF) where applicable.
• Ambient lighting: Room lighting should be controlled to avoid reflections and glare that could affect interpretation.
• Diagnostic versus review displays: Primary diagnostic interpretation should be performed on appropriately specified diagnostic displays. Review displays for clinical reference may have lower specifications but should still provide adequate image quality for their intended purpose.

5.11 Digital Image Management

Digital radiography images are managed through a digital information pathway that includes acquisition, processing, storage, transfer and display. Several standards and systems are involved.

DICOM (Digital Imaging and Communications in Medicine) is the international standard for medical image communication. DICOM defines how images, patient information, examination details and exposure metadata are structured and transmitted. Correct DICOM data ensures that images are associated with the right patient, examination and study.

Key elements of digital image management include:

• Patient demographics: Correct patient name, identification number, date of birth and other identifiers must be verified before acquisition.
• Examination information: The correct examination type, body part, laterality and projection must be selected.
• Exposure information: Exposure factors, exposure indicators and dose metadata should be recorded in the DICOM header where supported.
• Image metadata: Processing parameters, detector information and equipment identifiers are stored with the image.
• PACS (Picture Archiving and Communication System): The system that stores, retrieves and distributes medical images within and between healthcare facilities.
• RIS (Radiology Information System) integration: Links imaging orders, patient scheduling, reporting and workflow management.
• Worklists: Digital worklists provide the radiographer with scheduled examinations, patient details and examination specifications, reducing the risk of wrong-patient or wrong-examination errors.
• Image storage and transfer: Images are stored on secure servers and can be transferred to clinicians, other facilities or external systems as required.
• Data integrity: Patient and examination information must not be altered or lost during acquisition, processing or transfer.
• Privacy and information governance: Patient images and data must be handled according to applicable data protection regulations and local information governance policies.

Correct patient and examination identification must be confirmed before image acquisition. Acquiring an image on the wrong patient or performing the wrong examination is a serious clinical error that digital technology cannot prevent — only the radiographer can ensure correct identification.

Exposure-related information and relevant metadata should not be inadvertently altered or lost. This information supports dose monitoring, repeat/reject analysis and quality assurance, and it may be required for regulatory compliance.

5.12 Digital Radiography and Radiation Dose

Digital radiography does not inherently reduce or increase patient dose — the dose delivered depends on the technique selected, the detector performance and the optimisation practice. Digital technology provides tools that can help optimise dose, but it also introduces risks such as exposure creep that can increase dose if not monitored.

Key dose considerations in digital radiography:

• Detector exposure: The amount of radiation reaching the detector. This is what the exposure indicator reflects.
• Patient radiation dose: The amount of radiation absorbed by the patient. This depends on kVp, mAs, field size, patient thickness, grid use, filtration and other factors — not just detector exposure.
• Exposure optimisation: Selecting the combination of kVp, mAs, grid, collimation and AEC settings that produces a diagnostically adequate image at the lowest reasonable dose.
• Relationship between kVp, mAs and detector exposure: Increasing kVp or mAs generally increases detector exposure. The relationship is not linear and depends on the imaging system and patient factors.
• Patient thickness: Thicker patients attenuate more radiation and may require higher exposure, increasing dose.
• Collimation: Reduces irradiated volume and scatter, supporting both image quality and dose reduction.
• Grid use: Improves contrast but generally requires increased exposure, increasing patient dose.
• AEC: Helps maintain appropriate detector exposure but must be used correctly to avoid overexposure.
• Repeat exposures: Each repeat adds radiation dose. Avoiding unnecessary repeats is a key dose optimisation measure.
• Exposure creep: Gradual increases in exposure over time, concealed by wide exposure latitude.
• Dose monitoring: Departmental dose monitoring, exposure indicator tracking and comparison with DRLs help identify trends and optimise practice.
• Diagnostic Reference Levels (DRLs): Used as optimisation benchmarks, not as individual patient dose limits.

Exposure Index is not the same thing as patient dose.

DRLs are optimisation tools, not individual patient dose limits. Medically exposed patients are treated differently from occupational and public exposure in radiation protection frameworks, because the exposure is intended to provide a direct clinical benefit to the patient.

Dose optimisation should be applied across all clinical settings:

• General radiography: Use technique charts, appropriate collimation, grid selection and AEC correctly. Monitor exposure indicators.
• Mobile radiography: Adapt technique to the clinical environment. Use distance for staff protection. Ensure appropriate collimation and detector positioning. Be aware that mobile equipment may have different performance characteristics than fixed installations.
• Paediatric radiography: Use size-appropriate technique charts, careful collimation, appropriate immobilisation and avoid unnecessary repeats. Children are more sensitive to radiation and require particular attention to optimisation.
• Trauma imaging: Balance the need for rapid imaging with appropriate technique. Avoid unnecessary repeats where possible, but recognise that clinical circumstances may require adaptation of standard positioning.

ALARA and optimisation principles are discussed in greater detail in X-Ray Fundamentals → Radiation Protection & Dose Optimisation.

5.13 Quality Assurance in Digital Radiography

Quality assurance (QA) in digital radiography ensures that equipment performs consistently and that images are of adequate diagnostic quality while keeping patient exposure as low as reasonably achievable.

Equipment QA

• Detector performance: Regular testing of detector function, uniformity and image quality.
• Uniformity: Checking that the detector produces a consistent response across its entire surface.
• Artefact evaluation: Identifying and investigating persistent artefacts that may indicate detector problems.
• Calibration: Regular calibration of the detector and processing system according to manufacturer specifications.
• AEC performance: Testing that AEC chambers terminate exposure correctly and consistently.
• Exposure reproducibility: Verifying that repeated exposures under identical conditions produce consistent results.
• Image quality testing: Using test phantoms or objects to assess resolution, contrast, noise and artefact levels.

Clinical QA

• Repeat and reject analysis: Systematically reviewing repeated and rejected images to identify common causes and implement corrective action.
• Exposure indicator monitoring: Tracking exposure indicators over time to detect exposure creep or systematic technique errors.
• Dose monitoring: Comparing typical doses with DRLs and investigating outliers.
• Technique chart review: Regularly reviewing and updating technique charts when equipment, detectors or protocols change.
• Protocol review: Ensuring that examination protocols remain appropriate and optimised.
• Image quality assessment: Ongoing evaluation of clinical image quality by radiographers and radiologists.

Preventive QA

• Equipment maintenance: Scheduled maintenance by service engineers.
• Detector care: Handling detectors according to manufacturer guidelines to prevent damage.
• Cleaning: Regular cleaning of detector surfaces, cassettes and reader components.
• Calibration: Scheduled calibration as specified by the manufacturer.
• Software updates: Applying manufacturer software updates where relevant to maintain processing performance and security.
• Fault reporting: Prompt reporting of equipment faults or unusual behaviour for investigation and repair.

QA involves multiple roles:

• Radiographers: Responsible for correct technique, image evaluation, exposure indicator monitoring, repeat/reject recording and identifying equipment issues.
• Medical physics / medical physicists: Provide expertise in equipment testing, dose optimisation, DRL establishment and QA programme design.
• Service engineers: Perform scheduled maintenance, calibration and repair.
• Radiologists / clinicians: Provide feedback on image quality and diagnostic adequacy.
• Department management: Ensure QA programmes are implemented, resourced and maintained.

QA requirements vary according to jurisdiction, equipment and local policy. Applicable national regulations, professional standards and departmental protocols must be followed.

5.14 Mobile and Portable DR

Mobile digital radiography brings the imaging system to the patient rather than bringing the patient to the imaging department. Mobile DR systems use wireless flat-panel detectors that communicate with a mobile X-ray unit, allowing images to be acquired and reviewed at the point of care.

Key considerations for mobile DR:

• Mobile DR systems: Typically consist of a mobile X-ray generator and a wireless detector. The image is transmitted to the mobile unit's workstation for immediate review.
• Wireless detectors: Must be handled carefully to avoid impact damage. Battery life and charge status should be checked before use.
• Detector handling: Wireless detectors are expensive and sensitive to physical damage. Proper handling and storage are essential.
• Wireless communication: Image transfer depends on reliable wireless connectivity. Network issues can delay image availability.
• Infection prevention: Detectors and equipment must be cleaned between patients according to local infection-control protocols. Detector covers may be used where appropriate.
• Patient identification: Correct patient identification is particularly important in mobile settings, where workflow pressures and the clinical environment may increase the risk of errors.
• Exposure selection: Mobile units may have different generator capabilities than fixed installations. Technique charts should be specific to the mobile equipment.
• Positioning limitations: Patients may be unable to cooperate with standard positioning. The radiographer must adapt while maintaining the diagnostic objective.

Common mobile DR clinical settings include:

• Portable chest imaging: Performed with the patient typically in the erect or semi-erect position. Careful attention to detector positioning, centring and breathing instructions is essential.
• ICU: Patients may have multiple lines, tubes and monitoring equipment. Positioning must accommodate these devices. Exposure should be optimised for patients who may require repeated imaging.
• Emergency department: Rapid imaging is often needed for trauma or acutely unwell patients. The radiographer must balance speed with appropriate technique and radiation protection.
• Isolation rooms: Infection-control procedures must be followed. Equipment cleaning and detector handling require particular attention.
• Operating theatre: Mobile DR or C-arm fluoroscopy may be used. Sterile technique and theatre protocols must be observed.

Radiation protection in mobile DR requires particular attention because structural shielding may not be available:

• Staff positioning: Staff should maximise distance from the patient and X-ray source during exposure.
• Distance: The inverse-square law applies — doubling distance reduces intensity to approximately one quarter.
• Patient and staff scatter: The patient is the primary source of scattered radiation. Staff should position themselves to minimise scatter exposure.
• Other patients and staff: People in adjacent areas should be considered. Collimation and appropriate exposure reduce scatter.
• Primary beam awareness: No one should remain in the primary beam during exposure. Protective shielding should be used where available and appropriate.

Digital workflow can improve efficiency in mobile radiography through immediate image review, reducing the need to return to the department to check image quality. However, efficiency does not remove the need for careful technique, positioning and dose optimisation.

5.15 Paediatric DR

Children require particular attention in digital radiography because they are more sensitive to radiation than adults, and their smaller size means that technique charts and protocols must be adapted accordingly.

Key considerations for paediatric DR:

• Patient size: Exposure factors must be adapted to the child's size and age. Adult techniques should never be applied to children without appropriate adjustment.
• Age and development: The child's developmental stage affects their ability to cooperate. Communication should be age-appropriate.
• Communication: Clear, simple explanations help reduce anxiety and improve cooperation, which reduces motion and repeat risk.
• Immobilisation: Appropriate immobilisation devices may be necessary to maintain position. Radiolucent positioning aids should be used. Parents or carers may assist with immobilisation where appropriate and permitted by local policy.
• Exposure selection: Paediatric technique charts should be size-based and equipment-specific. Lower kVp and mAs are typically used for children, but the exact values depend on the examination, equipment and clinical indication.
• AEC considerations: AEC may not be appropriate for very small children because the chamber size may be larger than the anatomy of interest. Manual technique may be preferred for infants and small children.
• Avoiding repeat exposures: Every effort should be made to obtain a diagnostic image on the first exposure, as each repeat adds radiation dose to a more sensitive patient.
• Exposure indicators: Exposure indicators should be monitored for paediatric examinations, but target ranges may differ from adult values. Local paediatric protocols should specify appropriate targets.
• Dose monitoring: Paediatric doses should be monitored separately from adult doses, and paediatric DRLs should be used where available.
• Child-friendly workflow: A calm, supportive environment helps reduce anxiety and motion. Distraction techniques and clear communication are valuable.
• Parent and carer considerations: Parents or carers may remain with the child during exposure where permitted by local policy. If they remain, they must be provided with appropriate shielding and must not be in the primary beam.
• Neonatal and intensive-care imaging: Neonatal and paediatric intensive-care patients require particular attention. Exposure should be minimised while maintaining diagnostic quality, and the clinical condition of the patient may limit positioning options.

Paediatric protocols should be appropriately adapted to patient size and clinical need rather than simply applying adult techniques.

5.16 Common DR Errors

5.17 Clinical Digital Radiography Workflow

The following workflow integrates the key steps of a digital radiographic examination into a practical sequence:

1. Verify patient identity.
2. Confirm examination and clinical indication.
3. Assess patient condition, mobility and ability to cooperate.
4. Select appropriate protocol on the imaging system.
5. Select the correct detector for the examination.
6. Position the patient according to the examination requirements.
7. Select SID and set up the geometric relationship.
8. Select exposure factors or AEC chambers appropriate for the examination and patient size.
9. Collimate to the required anatomy before exposure.
10. Provide breathing and motion instructions to the patient.
11. Perform the exposure.
12. Review the exposure indicator where available.
13. Evaluate image quality — anatomy, positioning, exposure, motion, artefacts.
14. Check that correct anatomy, positioning and side markers are demonstrated.
15. Decide whether the image is diagnostically adequate.
16. Avoid unnecessary repeats — only repeat when clinically justified.
17. Apply appropriate post-processing if needed.
18. Confirm patient and examination data are correct.
19. Send or store the image through PACS as appropriate.
20. Complete documentation and workflow requirements.

Image evaluation should occur before the patient leaves whenever practical, so that a necessary repeat can be performed safely and efficiently without requiring the patient to return later.

5.18 Key Learning Points

• CR uses photostimulable phosphor plates in cassettes; DR uses flat-panel detectors that acquire images directly.
• Direct conversion converts X-rays to electrical charge via a photoconductor; indirect conversion converts X-rays to light first, then to charge.
• Detector function determines efficiency, speed and image quality characteristics.
• Digital image formation involves pre-processing, image recognition, histogram analysis and image processing.
• Pixel size, matrix size, bit depth and sampling determine the fundamental digital image characteristics.
• Dynamic range is the range of exposures over which the detector produces usable signal; digital systems generally have wide dynamic range.
• DQE describes how efficiently the detector converts incoming X-ray information into useful output signal.
• Image processing (LUTs, rescaling, edge enhancement, windowing) converts raw data into a clinically useful image but cannot recover unacquired information.
• Histogram analysis identifies the exposure field and determines processing parameters; appropriate collimation is essential.
• Exposure indicators reflect detector exposure, not patient dose.
• EI is not the same as patient absorbed dose — it is a detector-based metric.
• Deviation Index indicates how far the actual exposure deviates from the target, where supported.
• Exposure creep is the gradual increase in exposure concealed by wide exposure latitude.
• AEC terminates exposure based on detected radiation but requires correct chamber selection and positioning.
• Digital image quality depends on contrast, resolution, noise, sharpness and distortion — processing modifies appearance but cannot replace accurate acquisition.
• Artefacts may arise from the detector, acquisition, processing or equipment — investigate before repeating.
• DICOM is the standard for medical image communication; PACS manages storage and distribution.
• Dose optimisation requires technique charts, collimation, grid selection, AEC, exposure indicator monitoring and DRL comparison.
• DRLs are optimisation benchmarks, not individual patient dose limits.
• QA includes equipment testing, clinical monitoring and preventive maintenance.
• Mobile DR requires adaptation to the environment, careful detector handling and attention to staff radiation protection.
• Paediatric DR requires size-appropriate techniques, careful collimation and avoidance of unnecessary repeats.
• Image evaluation must confirm diagnostic adequacy before the examination is completed.

5.19 Quick Reference

Requirements and implementation may vary according to local regulations, equipment specifications and departmental protocols. Typical exposure values, exposure index targets and DRL values are illustrative only and should not be applied without reference to manufacturer guidance and local protocols.

Radiation Protection & Dose Optimisation

6.1 ALARA

ALARA stands for As Low As Reasonably Achievable. It is a cornerstone principle of radiation protection, widely promoted by the ICRP and embedded in radiation-protection frameworks worldwide.

ALARA does not mean using the lowest possible exposure regardless of image quality. An exposure that is too low may fail to provide the required diagnostic information, leading to a repeat examination and a potentially higher cumulative dose than a single appropriately optimised exposure.

Instead, exposure should be:

• Appropriate for the clinical task.
• Sufficient to obtain the required diagnostic information.
• Optimised according to patient size and examination.
• Consistent with equipment capability and local protocols.
• Avoiding unnecessary exposure and avoidable repeat examinations.

The radiographer must therefore balance:

Image quality ↔ Diagnostic information ↔ Radiation dose

ALARA is not a single number or a universal technique chart; it is a principle that guides every exposure decision toward an appropriate balance between clinical value and radiation risk.

6.2 Justification

Justification is the first and most fundamental step in radiation protection. Before any examination involving ionising radiation is performed, it must be clinically justified.

Justification involves considering:

• Whether there is an appropriate clinical indication for the examination.
• Whether the examination is necessary or whether the clinical question could be answered by previous imaging already available.
• Whether another imaging method could answer the clinical question without ionising radiation where appropriate and clinically equivalent.
• Whether the likely benefits of the examination outweigh the potential radiation risk.

The exact legal responsibility for justification varies between jurisdictions. In many countries, the referrer, the practitioner responsible for the examination and the imaging professional each have defined roles in the justification process. The radiographer should follow local referral and justification procedures and should raise concerns about unjustified or inappropriate examinations through the appropriate local channels.

A justified examination should not be cancelled simply because radiation is involved. The purpose of justification is to ensure that the benefit exceeds the risk, not to prevent all radiation exposure. Once an examination is justified, attention shifts to optimisation.

6.3 Patient Radiation Protection

Patient radiation protection encompasses all measures that reduce unnecessary radiation exposure while ensuring the examination achieves its diagnostic purpose.

Key measures include:

• Correct patient identification before exposure.
• Correct examination and anatomical region, including appropriate laterality.
• Appropriate clinical indication confirmed before proceeding.
• Pregnancy considerations where relevant to the examination and patient.
• Appropriate patient positioning to demonstrate the required anatomy.
• Appropriate exposure factors selected for the examination and patient size.
• Patient-size and body-habitus adjustment rather than using a single technique for all patients.
• Appropriate collimation to restrict the beam to the required anatomy.
• Correct SID and geometric setup for the examination.
• Appropriate grid use based on patient thickness, examination and equipment.
• Appropriate use of AEC, including correct chamber selection and positioning.
• Appropriate detector selection and positioning.
• Avoiding unnecessary repeat examinations.
• Monitoring exposure indicators in digital radiography.
• Following equipment-specific technique charts rather than generic values.
• Special optimisation for paediatric patients, who are more sensitive to radiation.
• Optimisation for patients requiring repeated or serial examinations.

Accurate positioning is itself a radiation-protection measure. Poor positioning is one of the most common causes of repeat imaging, and each repeat adds an additional radiation exposure. By positioning the patient correctly the first time, the radiographer helps prevent unnecessary additional dose.

6.4 Time, Distance and Shielding

The three fundamental practical principles of radiation protection are time, distance and shielding. These apply to both staff and anyone else who may be exposed to radiation during an examination.

Time

Minimising unnecessary exposure time reduces the total radiation received. In radiography, exposure time is primarily controlled by the equipment and the selected technique. However, the principle of minimising time is particularly relevant in:

• Radiography: Using appropriate exposure times to minimise motion and avoid repeats.
• Mobile radiography: Minimising the time spent close to the patient during exposure.
• Fluoroscopy: Keeping fluoroscopy time as short as clinically possible.
• Operating theatre imaging: Minimising screening time and the number of spot images.

Distance

Increasing distance from the radiation source is one of the most effective methods of reducing exposure. Radiation intensity decreases with the square of the distance from the source, a relationship described by the inverse-square law:

Intensity ∝ 1 / distance²

For example, if the distance from the source is doubled, the radiation intensity falls to approximately one-quarter of its original value, assuming other conditions remain unchanged. Conversely, halving the distance increases intensity by approximately four times.

This principle is particularly important for staff and other people exposed to scattered radiation from the patient. During mobile radiography, for instance, stepping further away from the patient during exposure substantially reduces occupational dose.

Shielding

Shielding provides an additional layer of protection by absorbing or attenuating radiation before it reaches people. Types of shielding include:

• Structural shielding: The walls, doors and protective barriers built into radiographic rooms.
• Protective barriers: Mobile or fixed screens used in operating theatres, fluoroscopy suites and mobile radiography.
• Personal protective equipment (PPE): Lead or lead-equivalent protective garments, thyroid shields, protective eyewear and protective gloves where appropriate.

Shielding should be used according to the relevant risk assessment, local regulations and departmental policy. It should not be assumed that personal lead shielding is universally mandatory for every radiographic examination. Current international guidance and local policy should be followed regarding patient shielding, as practices differ between countries and have evolved in recent years.

Time and distance, especially maximising distance from the patient during exposure, are fundamental controls. Shielding is an additional protective measure used where appropriate.

6.5 Radiation Protection of Staff

Occupational radiation exposure of radiographic staff is predominantly associated with scattered radiation from the patient, rather than from deliberately entering the primary beam. During a diagnostic X-ray exposure, the patient becomes a source of scattered radiation, and anyone close to the patient may receive a small radiation dose.

Key staff-protection measures include:

• Never deliberately entering the primary X-ray beam.
• Maximising distance from the patient and X-ray source during exposure.
• Using structural barriers or mobile protective screens where available.
• Appropriate positioning behind shielding during exposure.
• Minimising the time spent close to the patient during exposure.
• Wearing personal dosimetry where required by local policy.
• Following local radiation-safety procedures and protocols.
• Considering pregnancy-related occupational requirements according to applicable regulations.
• Completing appropriate radiation-safety training.
• Reporting unusual radiation incidents or exposures through the appropriate local process.

Personal dosimetry helps monitor cumulative occupational exposure and supports compliance with applicable dose limits. The exact requirements for dosimetry, dose limits and pregnancy-related occupational restrictions differ between jurisdictions and should be followed according to local regulations.

6.6 Radiation Protection of Other People

Radiation protection also extends to other people who may be present during an examination, including:

• Other patients in the vicinity.
• Relatives and carers.
• Students and trainees.
• Other healthcare workers.
• Theatre staff.
• Ward staff.
• Visitors.

People should not remain in the room during exposure unless their presence is necessary and permitted under local procedures. When someone must remain with the patient, for example a parent supporting a child or a nurse managing critical equipment, the following measures should be taken:

• Maximise distance from the patient and X-ray source.
• Use appropriate shielding, such as a protective apron, where provided.
• Ensure the person is never in the primary beam.
• Follow local radiation-protection procedures.
• Provide clear instructions before the exposure.

6.7 Collimation and Field Size

Collimation is one of the most practical and effective radiation-protection tools available to the radiographer. By restricting the X-ray field to the required anatomy, collimation:

• Reduces the volume of irradiated tissue.
• Reduces the amount of scatter produced.
• Improves image contrast by reducing scatter reaching the detector.
• Reduces unnecessary patient dose.
• Supports both image quality and radiation protection simultaneously.

The field should be large enough to include all clinically required anatomy but no larger than necessary. Excessive collimation that excludes clinically relevant anatomy can lead to a repeat examination, which defeats the dose-saving purpose. Correct positioning must therefore be achieved before collimation is finalised.

Good collimation simultaneously supports image quality and radiation protection.

6.8 Factors Affecting Patient Dose

The radiation dose received by a patient during a radiographic examination is influenced by many interrelated factors:

• kVp: Higher tube potential increases beam energy and penetration. It also increases X-ray output. The net effect on dose depends on whether mAs is adjusted accordingly.
• mAs: Increasing mAs increases the number of photons produced and generally increases patient dose.
• Exposure time: Longer exposure times increase the total radiation delivered, though in projection radiography the total dose is primarily determined by mAs.
• Patient thickness and composition: Larger or denser patients attenuate more radiation but may also require higher exposure factors, increasing dose.
• Field size: Larger fields irradiate more tissue and increase scatter, contributing to higher overall dose.
• SID: Changing SID alters radiation intensity at the detector and may require exposure compensation.
• OID: Affects geometric relationships and magnification but does not directly change the total energy delivered to the patient.
• Filtration: Removes low-energy photons that would otherwise be absorbed by the patient without contributing to the image.
• Grid use: Grids absorb scatter but also absorb some primary radiation, requiring increased exposure and increasing patient dose.
• AEC: AEC can help maintain appropriate detector exposure but depends on correct positioning and chamber selection.
• Detector characteristics: Detector efficiency influences the exposure required to produce a diagnostically useful image.
• Number of projections: Each additional projection adds radiation dose.
• Repeat examinations: Each repeat adds a further radiation exposure.
• Technique selection: The overall combination of factors determines the final patient dose.

These factors should not be considered in isolation. Increasing exposure generally increases radiation dose, while the effect of changing kVp or other individual factors depends on the imaging system, the technique strategy and whether compensating adjustments are made. Simplistic universal dose calculations should be avoided in favour of equipment-specific technique charts and local protocols.

6.9 Filtration and Beam Quality

Filtration modifies the X-ray beam by removing a proportion of low-energy photons that would be absorbed by the patient without significantly contributing to image formation. This process, known as beam hardening, results in a beam with a higher average photon energy.

Filtration may arise from:

• Inherent filtration: The filtration provided by the tube assembly, housing, oil and window.
• Added filtration: Deliberately added material, such as aluminium or copper filters, inserted into the beam path.

Appropriate total filtration reduces unnecessary patient skin exposure by removing low-energy photons while maintaining sufficient beam quality for diagnostic imaging. The total filtration required for a diagnostic system is determined by equipment design and applicable standards or regulations, which differ between jurisdictions.

6.10 Grids and Radiation Dose

Anti-scatter grids are positioned between the patient and detector to reduce the amount of scattered radiation reaching the detector. By reducing scatter, grids improve image contrast, particularly when imaging thicker anatomy.

However, grids also absorb some primary radiation. This means that grid use generally requires increased exposure, which increases patient dose. Grid selection should therefore consider:

• Patient thickness
• Examination type
• Grid ratio and frequency
• kVp
• Detector technology
• SID and centring

A grid should be used when clinically appropriate and according to departmental protocol, not applied routinely to every examination. Using a grid when it provides little clinical benefit unnecessarily increases patient dose. Correct grid alignment is also essential, as misalignment can produce grid cut-off and lead to repeat imaging.

Grid use involves a trade-off between scatter reduction, image quality and increased exposure.

6.11 Digital Radiography and Dose Optimisation

Digital radiography provides a wide exposure latitude, meaning that an image can appear visually acceptable over a relatively broad range of detector exposures. While this is an advantage in many clinical situations, it also introduces a risk known as exposure creep.

Exposure creep occurs when exposure factors gradually increase over time without an obvious deterioration in displayed image appearance, because digital processing compensates for the increased detector exposure. The patient receives a higher dose, but the image looks similar.

Key principles for dose optimisation in digital radiography include:

• Image brightness alone cannot determine whether the exposure was appropriate.
• Exposure indicators provided by the imaging system should be monitored and compared with equipment-specific target ranges.
• Technique charts should be developed for the specific imaging system and updated when equipment or detectors change.
• Unnecessary increases in mAs should be avoided.
• Post-processing cannot remove radiation already delivered to the patient.

A visually acceptable digital image can still have been acquired using an unnecessarily high exposure.

6.12 Repeat and Reject Analysis

Repeat and reject analysis is an important quality-improvement and radiation-protection tool. By systematically reviewing repeated and rejected images, departments can identify common causes and take corrective action.

Common causes of repeat imaging include:

• Positioning errors
• Motion
• Incorrect exposure factors
• Incorrect patient identification
• Wrong examination performed
• Collimation errors
• Artefacts
• Equipment or detector problems
• Communication failures

Preventing an unnecessary repeat prevents an unnecessary additional radiation exposure.

It is important to distinguish between:

• Avoidable repeats: Those caused by positioning, technique or communication errors that could have been prevented.
• Clinically unavoidable repeats: Those required because the clinical situation changed or the patient's condition prevented adequate cooperation.
• Equipment-related repeats: Those caused by equipment or detector failure.

Repeating an image merely for cosmetic perfection when the diagnostic objective has already been achieved is not appropriate and adds unnecessary radiation dose. Each repeat should be clinically justified.

6.13 Radiation Dose Quantities

Several radiation dose quantities are relevant to diagnostic imaging. They serve different purposes and should not be treated as interchangeable.

Absorbed dose: The energy deposited by ionising radiation per unit mass of tissue. It is the fundamental physical dose quantity.

Equivalent dose: Absorbed dose weighted for the type of radiation, accounting for the differing biological effectiveness of different radiation types. In diagnostic X-ray imaging, the weighting factor is 1, so equivalent dose and absorbed dose have the same numerical value.

Effective dose: Equivalent dose further weighted for the radiosensitivity of different organs and tissues. Effective dose is primarily a radiation-protection quantity used for comparing and communicating stochastic risk at a population or reference level. It is not a direct prediction of an individual patient's cancer risk.

Air kerma: Kinetic energy released per unit mass of air. It is commonly used to describe the radiation output of an X-ray tube or the dose rate at a particular point.

Kerma-area product (KAP) / dose-area product (DAP): The product of air kerma and the area of the X-ray field. It provides an indication of the total radiation delivered during an examination and is commonly used in fluoroscopy.

Entrance surface dose (ESD): A measure of the dose at the surface of the patient where the X-ray beam enters. It is commonly used for assessing patient dose in projection radiography.

These quantities help radiographers and physicists communicate about radiation dose, but they should be understood in context rather than treated as a single universal number.

6.14 Diagnostic Reference Levels

Diagnostic Reference Levels (DRLs) are dose levels used to help optimise radiographic technique and identify unusually high exposures.

DRLs are:

• Established using representative patient groups and standard examinations.
• Used as a comparison tool to assess whether typical doses for a particular examination are within an expected range.
• Not individual patient dose limits.
• Not regulatory limits that must not be exceeded for any single examination.

DRL ≠ patient dose limit

DRL values vary between countries, institutions, equipment types and examination protocols. When local or national DRLs are available, they should be used as part of a departmental optimisation process. If typical doses for a particular examination consistently exceed the DRL, an investigation should be conducted to identify possible causes and implement corrective action.

6.15 Paediatric Radiation Protection

Children are more sensitive to radiation than adults, and their longer remaining lifespan means that any potential radiation-related risk has more time to manifest. Paediatric radiation protection therefore requires particular attention.

Key considerations include:

• Justification: Ensuring the examination is clinically indicated and that the benefits outweigh the risks.
• Optimisation: Selecting exposure factors appropriate for the child's size rather than using adult settings without adjustment.
• Patient-size-based exposure selection: Using dedicated paediatric technique charts or protocols.
• Appropriate collimation: Restricting the field to the required anatomy, which is particularly important for children.
• Avoiding unnecessary repeats: Using immobilisation, clear communication and appropriate technique to reduce the likelihood of motion-related repeats.
• Appropriate immobilisation: Using radiolucent positioning aids or specialised paediatric immobilisation devices where necessary.
• Communication: Explaining the examination to the child and their parent or carer to improve cooperation and reduce motion.
• Dedicated paediatric protocols: Following departmental or manufacturer paediatric protocols where available.

Shielding practices for paediatric patients should follow current local policy and professional guidance, which may differ from historical practice.

6.16 Pregnancy and Radiation Protection

Pregnancy considerations in radiography require a balanced approach that avoids both unnecessary radiation exposure and unnecessary fear or delay of clinically important imaging.

Key principles include:

• Establishing whether pregnancy information is relevant to the examination, particularly for examinations involving the abdomen or pelvis.
• Following local pregnancy-screening procedures before performing examinations where the fetus may be in the primary beam.
• Ensuring the examination is clinically justified.
• Optimising the technique to minimise dose while maintaining diagnostic quality.
• Considering the anatomical region and the distance between the examination site and the fetus; many examinations, such as extremity or chest radiography, involve minimal fetal dose.
• Special consideration for examinations involving the abdomen or pelvis, where the fetus may receive a higher dose.
• Avoiding unnecessary delay of clinically justified imaging, as delaying a necessary examination can also carry clinical risk.
• Following local pregnancy-screening and radiation-safety policies, which differ between jurisdictions.

X-ray examinations are not automatically contraindicated during pregnancy. A clinically justified examination that provides important diagnostic information may be appropriate, provided the technique is optimised. The exact procedures for managing pregnant or potentially pregnant patients vary according to jurisdiction and local policy.

For radiation workers who are pregnant, occupational radiation-protection requirements apply according to applicable national regulations and local employer policy.

6.17 Mobile and Portable Radiography

Mobile radiography introduces additional radiation-protection challenges because examinations are performed outside the controlled environment of a radiographic room.

Practical radiation-protection measures for mobile radiography include:

• Preparing the environment before bringing the X-ray equipment into the room or bay.
• Identifying people who need to remain in the area and ensuring others move away.
• Maximising distance from the patient and X-ray source during exposure.
• Using mobile protective barriers where available.
• Ensuring no one is in the primary beam.
• Communicating clearly with nearby staff before exposure.
• Considering infection-control requirements alongside radiation protection.
• Minimising unnecessary exposure to nearby patients, particularly in shared wards or open-plan units.

These principles apply across ward imaging, intensive care, emergency departments, neonatal units and isolation rooms.

6.18 Fluoroscopy and Operating Theatre Radiation Protection

Fluoroscopy and intraoperative imaging involve prolonged or repeated radiation exposure, which introduces additional radiation-protection considerations compared with standard projection radiography.

Important considerations include:

• Fluoroscopy time: Keeping screening time as short as clinically possible.
• Dose rate: Using the lowest dose rate consistent with the clinical requirement.
• Pulsed fluoroscopy: Using pulsed rather than continuous fluoroscopy where available to reduce dose.
• Collimation: Restricting the field to the required anatomy throughout the procedure.
• Magnification: Avoiding unnecessary magnification, which increases dose rate.
• Patient positioning: Positioning the patient appropriately relative to the detector and tube.
• Staff distance: Maximising distance from the patient and tube during screening.
• Scatter: Recognising that the patient is the primary source of scattered radiation during fluoroscopy.
• Protective barriers and PPE: Using ceiling-suspended screens, table curtains, protective aprons, thyroid shields and protective eyewear where appropriate.
• Radiation monitoring: Using personal dosimetry and monitoring cumulative occupational exposure.

Staff exposure can become particularly important in procedures involving prolonged fluoroscopy, such as interventional and surgical procedures. Cumulative occupational exposure should be monitored and managed according to local regulations.

6.19 Quality Assurance and Radiation Safety

Quality assurance (QA) is an essential component of radiation protection. Equipment that is not performing correctly can compromise both image quality and radiation safety.

A comprehensive QA programme may include:

• Equipment performance testing
• Preventive maintenance
• AEC testing and calibration
• Detector performance assessment
• Exposure reproducibility checks
• Radiation output verification
• Image-quality assessment
• Repeat and reject analysis
• Dose monitoring and DRL comparison
• Investigation of unusual dose levels
• Incident reporting
• Continuous quality improvement

The exact testing programme depends on the equipment, healthcare system and applicable regulations. Radiographers should recognise unexpected changes in equipment performance and report them through the appropriate local process.

6.20 Justification vs Optimisation vs Dose Limits

One of the most important concepts in radiation protection, and a common topic in radiography examinations and essays, is the distinction between justification, optimisation and dose limits.

Justification

Should the examination be performed?

Justification determines whether a proposed examination involving ionising radiation is clinically appropriate. It considers whether the expected benefits outweigh the potential risks.

Optimisation

How can the examination provide the required diagnostic information with an appropriate level of radiation exposure?

Optimisation ensures that, once justified, the examination is performed with techniques that deliver the necessary diagnostic information while keeping radiation exposure as low as reasonably achievable.

Dose Limits

Dose limits generally apply to occupational and public exposure, not to medically justified patient exposures. Patient exposures are managed through justification and optimisation rather than by applying occupational or public dose limits to individual diagnostic examinations.

This means that a patient may receive a dose that exceeds an occupational dose limit if the examination is justified and optimised, because the clinical benefit justifies the exposure. The exact legal requirements for dose limits differ by jurisdiction.

Occupational and public dose limits should not be confused with patient medical exposure, which is governed by justification and optimisation.

6.21 Practical Radiation Protection Checklist

A concise clinical checklist for routine radiographic practice:

• Correct patient identified
• Correct examination confirmed
• Appropriate clinical indication verified
• Relevant pregnancy considerations addressed
• Appropriate positioning achieved
• Appropriate exposure factors selected for patient size and examination
• Correct collimation applied
• Appropriate detector selected and positioned
• Appropriate grid used where clinically indicated
• Appropriate AEC chamber(s) selected where used
• Repeats minimised
• Exposure indicator checked after exposure
• Image evaluated for diagnostic acceptability before repeating
• Staff distance maximised during exposure
• Barriers and PPE used where appropriate
• Local radiation-safety procedures followed

6.22 Common Radiation-Protection Errors

6.23 Key Learning Points

• Justification comes before exposure.
• Optimisation follows justification.
• ALARA means appropriate optimisation, not simply the lowest possible exposure.
• Time, distance and shielding are fundamental radiation-protection principles.
• Collimation reduces unnecessary irradiation and scatter.
• Accurate positioning helps prevent repeat exposure.
• Digital processing does not eliminate radiation dose.
• Exposure indicators help monitor detector exposure.
• Avoid exposure creep in digital radiography.
• Repeat and reject analysis supports dose reduction.
• Children require particular attention to optimisation.
• Pregnancy does not automatically prohibit medically justified X-ray imaging.
• Staff should maximise distance and avoid the primary beam.
• DRLs support optimisation but are not individual patient dose limits.
• Occupational and public dose limits should not be confused with patient medical exposure.
• Local legislation and departmental procedures must always be followed.

6.24 Quick Reference

Patient Safety & Image Optimisation

7.1 The Six Questions of Safe Radiography

Structured clinical reasoning helps the radiographer make safe, effective decisions for every examination. The following six questions provide a framework that encourages thinking rather than mechanical application of routine projections.

1. Why? What is the clinical indication? Is the examination justified?

2. Who? Is this the correct patient and the correct examination?

3. What? What anatomy and diagnostic information are required?

4. How? What positioning, projection and technique are appropriate for this patient?

5. How much? What exposure is appropriate for this patient, examination and equipment?

6. Is it good enough and safe? Does the image meet diagnostic requirements while maintaining patient and staff safety?

These questions are not a formality; they are a practical tool for preventing errors and ensuring that every examination is tailored to the individual patient and clinical situation.

7.2 Patient Identification and Examination Verification

Correct patient identification is a fundamental patient-safety requirement, not merely an administrative task. Failure to correctly identify a patient can lead to wrong-patient imaging, wrong-examination imaging, wrong anatomical side, unnecessary radiation exposure and delayed or incorrect clinical management.

The radiographer should:

• Identify the patient using appropriate identifiers according to local policy.
• Confirm the requested examination and anatomical region.
• Confirm laterality where relevant.
• Confirm the clinical indication.
• Compare with previous imaging where relevant and available.
• Verify the correct examination has been selected on the imaging system.
• Confirm identity immediately before exposure.

The exact identification procedures and identifiers used differ between jurisdictions and institutions. Local policy, national patient-safety standards and professional requirements must always be followed.

7.3 Clinical Assessment Before Imaging

The radiographer should assess the patient's condition before deciding how to perform the examination. The standard textbook position may not always be appropriate for the individual patient.

The assessment should consider:

• Mobility and ability to stand, sit or lie safely.
• Pain level and location.
• Level of consciousness.
• Ability to understand and follow instructions.
• Respiratory status.
• Neurological condition where relevant.
• Recent surgery.
• Immobilisation devices, casts and splints.
• Drains, lines and monitoring equipment.
• Infection-control requirements.
• Risk of falls.
• Need for assistance or additional staff.
• Trauma precautions.

Based on this assessment, the radiographer may need to modify positioning, technique, projection or workflow to ensure the examination is performed safely and effectively.

7.4 Communication, Consent and Patient Dignity

Clear, respectful communication is essential for patient safety and image quality. The radiographer has a professional responsibility to communicate effectively with every patient.

Key communication practices include:

• Introduce yourself and explain the examination.
• Explain what the patient needs to do and what to expect.
• Explain positioning before moving the patient.
• Give clear breathing instructions and confirm understanding.
• Allow appropriate opportunity for questions.
• Consider language and communication barriers; use interpreters or communication aids where appropriate.
• Maintain privacy and protect dignity during positioning and changing.
• Expose only the area necessary for the examination.
• Respect cultural and individual needs within professional and safety requirements.
• Explain potentially uncomfortable positions before performing them.

Good communication can reduce anxiety, movement, positioning errors, repeat exposures and patient refusal or non-cooperation. The exact consent and communication requirements may differ between jurisdictions; local policy and professional standards should be followed.

7.5 Safe Patient Movement and Manual Handling

Patient movement is an important part of radiographic safety. The radiographer frequently assists patients onto and off imaging tables, repositions them for different projections and transfers patients between beds, trolleys and wheelchairs.

Key principles for safe patient movement include:

• Assess the patient's mobility before attempting movement.
• Assess fall risk before asking the patient to stand or transfer.
• Use appropriate transfer equipment such as sliding sheets, hoists or transfer boards where indicated.
• Ask for assistance when required; do not attempt unsafe transfers alone.
• Use appropriate staff numbers for the patient's size and condition.
• Move patients with restricted mobility safely, using correct techniques.
• Manage wheelchair and trolley transfers carefully.
• Position the detector safely during bed-to-detector transfers.
• Move patients with lines, drains and monitoring equipment with care to avoid displacement.
• Maintain spinal precautions where indicated.
• Avoid unnecessary movement in trauma.
• Communicate with the wider healthcare team when assistance or clinical input is needed.

The safest imaging position is not necessarily the position that produces the most technically perfect projection if achieving it places the patient at risk.

7.6 Trauma and Patients with Limited Mobility

Trauma and limited mobility require the radiographer to adapt standard examinations to the patient's clinical condition. The patient's safety takes priority over achieving an ideal textbook position.

Adaptations may be needed for:

• Suspected spinal injury.
• Fractures and dislocations.
• Severe pain.
• Post-operative patients.
• Patients in casts or splints.
• Patients who cannot stand.
• Wheelchair users.
• Patients who cannot cooperate.
• Critically ill patients.

Key principles include:

• Avoid unnecessary movement.
• Maintain immobilisation where required.
• Use horizontal-beam techniques where appropriate.
• Adapt detector and tube positioning to the patient's condition.
• Use portable imaging where clinically appropriate.
• Accept modified positioning when the standard projection is not safe.
• Communicate with the clinical team.

Patient safety takes priority over achieving an ideal textbook position.

7.7 Infection Prevention and Control

Infection prevention and control (IPC) is an integral part of radiographic practice. The radiographer must follow appropriate IPC measures throughout the examination.

Key considerations include:

• Hand hygiene before and after patient contact.
• Appropriate personal protective equipment according to infection-control requirements.
• Cleaning and disinfection of equipment between patients.
• Detector cleaning according to manufacturer instructions.
• Cleaning of positioning aids and immobilisation equipment.
• Contact precautions for known or suspected infections.
• Isolation patients: following local isolation protocols.
• Mobile X-ray equipment: cleaning after use in isolation or contaminated areas.
• Avoiding cross-contamination between patients and between departments.
• Appropriate handling and disposal of contaminated equipment.
• Following local infection-prevention policies at all times.

Equipment cleaning procedures must be compatible with manufacturer instructions. Specific cleaning products and procedures vary between institutions and equipment types; local IPC policy should be followed.

7.8 Positioning as a Patient-Safety and Optimisation Tool

Accurate positioning contributes to both image quality and radiation protection. Poor positioning can result in non-diagnostic images, repeat exposures, additional patient dose and delayed diagnosis.

Positioning considerations that affect safety and optimisation include:

• Correct anatomical positioning to demonstrate the required anatomy.
• Rotation control to avoid misrepresentation of anatomical relationships.
• Correct detector placement to include all required anatomy.
• Appropriate central-ray alignment and angulation.
• Appropriate SID for the examination.
• Appropriate collimation to restrict the beam to the required anatomy.
• Use of anatomical landmarks for accurate centring.
• Correct side marker placement before exposure.
• Patient comfort to reduce motion and maintain cooperation.

Accurate positioning is simultaneously an image-quality measure and a radiation-protection measure, because it reduces the likelihood of repeat imaging.

7.9 Exposure Optimisation

Exposure selection should consider the individual patient and examination rather than applying fixed factors. The radiographer should consider:

• Patient size and body habitus.
• Anatomical region being imaged.
• Clinical question and diagnostic objective.
• Projection and positioning.
• Detector characteristics.
• Grid use and grid selection.
• AEC availability and chamber selection.
• kVp, mAs and exposure time.
• Local technique charts and equipment-specific protocols.

There is no single exposure technique that is appropriate for every patient.

The radiographer should adjust technique appropriately rather than simply applying fixed exposure factors. This principle is covered in more detail in the Radiation Protection & Dose Optimisation article.

7.10 Image Quality vs Radiation Dose

The optimisation balance can be understood as follows:

Too little exposure → increased noise → potentially reduced diagnostic information.

Appropriate exposure → sufficient diagnostic information → appropriate noise level → appropriate patient dose.

Excessive exposure → may produce little or no meaningful diagnostic benefit → increases patient radiation exposure.

The objective is not maximum image quality, but appropriate diagnostic image quality.

7.11 Digital Imaging and Exposure Creep

Digital radiography provides wide exposure latitude, meaning an image can appear visually acceptable over a broad range of detector exposures. This introduces the risk of exposure creep, where exposure factors gradually increase over time without an obvious deterioration in displayed image appearance.

The radiographer should:

• Monitor exposure indicators after each exposure.
• Compare exposure indicators with equipment-specific target ranges.
• Follow local technique charts and manufacturer guidance.
• Recognise that image brightness alone is not a reliable indicator of exposure adequacy.

Digital processing can improve image appearance, but it cannot undo radiation exposure already delivered to the patient.

7.12 Image Evaluation Before Completing the Examination

Every image should be evaluated before the patient is released or the examination is considered complete. Image acceptance should be based on diagnostic adequacy, not cosmetic perfection.

Anatomy:

• Is the required anatomy included?
• Is the clinically relevant region adequately demonstrated?

Positioning:

• Is the correct projection achieved?
• Is rotation acceptable?
• Is the anatomical region correctly aligned?

Exposure:

• Is penetration adequate?
• Is the detector exposure appropriate?
• Is noise acceptable?

Image quality:

• Is spatial detail sufficient?
• Is contrast acceptable?
• Is there significant motion?

Collimation:

• Is the field appropriately restricted?
• Is relevant anatomy excluded?

Marker:

• Is the correct side marker visible and correctly placed?

Artefacts:

• Are there any artefacts that could affect interpretation?

Clinical adequacy:

• Does the image answer the clinical question?

7.13 Repeat Imaging Decision-Making

When an image is suboptimal, the radiographer should decide whether a repeat is genuinely necessary by considering:

1. Is the image diagnostically acceptable?
2. What information is missing?
3. Is the deficiency clinically important?
4. Can the problem be corrected without repeating?
5. Would repeating the image materially improve diagnosis?
6. Does the benefit justify the additional radiation exposure?
7. Can the patient safely tolerate another exposure?

Do not repeat an image simply because it is not aesthetically perfect if it already provides the required diagnostic information.

7.14 Special Patient Groups

Paediatric Patients

• Communication appropriate to age and understanding.
• Appropriate immobilisation using radiolucent aids or specialised paediatric devices.
• Dose optimisation with size-appropriate technique charts.
• Repeat avoidance through preparation, communication and immobilisation.

Older or Frail Patients

• Assessment of mobility and falls risk.
• Pain consideration and appropriate pacing.
• Clear, unhurried communication.
• Transfer assistance and appropriate staffing.

Bariatric Patients

• Awareness of equipment weight limits and table capacity.
• Appropriate positioning and detector selection.
• Exposure adjustment for patient size.
• Avoiding equipment damage and patient injury.

Pregnant Patients

• Justification and appropriate optimisation.
• Examination-specific considerations based on anatomical region and distance from the fetus.
• Following local pregnancy-screening and radiation-safety procedures.

Unconscious or Confused Patients

• Careful identification and monitoring.
• Safe positioning with assistance.
• Communication with carers and the clinical team.

Patients with Disabilities

• Individualised communication and positioning adaptations.
• Appropriate assistance without making assumptions about capability.

7.15 Patient Safety During Mobile Radiography

Mobile imaging requires additional attention because the radiographer works in environments not designed as radiographic rooms. Key considerations include:

• Correct patient identification at the bedside.
• Confirming the examination and anatomical region.
• Equipment preparation before entering the patient area.
• Infection-control measures appropriate to the clinical setting.
• Safe detector placement, avoiding falls or entanglement.
• Managing lines, tubes and monitoring equipment.
• Communication with ward or ICU staff.
• Radiation protection of nearby patients and staff.
• Checking the image before leaving where practical.

7.16 Equipment and Environmental Safety

Equipment and environmental safety is part of overall patient safety. The radiographer should check:

• Equipment condition before use, including tube and table movement.
• Detector condition and integrity.
• Brakes and locks on tables and mobile equipment.
• Mobile equipment stability.
• Cable management to avoid trip hazards.
• Patient supports and immobilisation devices.
• Weight limits for tables and equipment.
• Emergency access and safe positioning around equipment.

Equipment malfunction or unsafe setup can create both patient-safety and image-quality problems.

7.17 Optimisation Through Workflow

Optimisation is not only about exposure factors. Good workflow can reduce patient waiting, anxiety, movement, repeat examinations, equipment handling errors, identification errors and unnecessary radiation exposure.

Effective workflow practices include:

• Preparation before bringing the patient into the room.
• Correct equipment selection and setup.
• Having the detector and side markers ready.
• Clear communication throughout.
• Efficient positioning without rushing.
• Checking the image before moving the patient.
• Appropriate documentation.

7.18 Human Factors and Communication

Errors in radiography can arise from human factors such as interruptions, fatigue, poor communication, assumptions, inadequate identification, poor teamwork, incomplete handover, time pressure and equipment unfamiliarity.

Practical safeguards include:

• Standardised identification and verification checks.
• Clear communication with the patient and the team.
• Verification before exposure.
• Effective teamwork.
• Speaking up when something appears incorrect.
• Following established safety procedures.

Recognising the influence of human factors helps the radiographer maintain safe practice even under challenging conditions.

7.19 Clinical Scenario-Based Optimisation

The following short scenarios demonstrate how the radiographer applies clinical reasoning to adapt the examination to the individual patient.

Scenario 1 — Unable to Stand

A patient referred for an erect chest examination cannot safely stand. The radiographer assesses the situation and adapts the examination, perhaps performing a seated or semi-erect projection, rather than placing the patient at risk of falls. The clinical objective — demonstrating the chest in as erect a position as safely possible — is achieved without compromising patient safety.

Scenario 2 — Trauma

A patient with suspected cervical spine injury cannot safely rotate the neck. The standard lateral projection may need modification, such as using a horizontal beam and adapting detector positioning to avoid moving the patient's head. The radiographer communicates with the trauma team and accepts a modified technique that prioritises spinal precautions.

Scenario 3 — Paediatric Patient

A child is unable to remain still. The radiographer uses age-appropriate communication, appropriate immobilisation, short exposure time and size-appropriate technique. The objective is to obtain a diagnostic image on the first attempt and avoid unnecessary repeat exposure.

Scenario 4 — Technically Imperfect Image

An image has minor positioning imperfections but clearly answers the clinical question. The radiographer evaluates the image against diagnostic criteria and determines that the diagnostic objective has been achieved. Repeating the image would add radiation exposure without providing meaningful clinical benefit.

Scenario 5 — Excessive Digital Exposure

A digital image appears excellent, but the exposure indicator is substantially above the local target range. The radiographer recognises that while the image is diagnostically acceptable, the technique requires review to prevent exposure creep. The exposure factors are adjusted for future examinations of this type and patient size.

7.20 The Integrated Radiographic Decision-Making Model

The following ten-step framework integrates the key decision points of a radiographic examination:

Step 1 — Clinical need: Why is the examination required?

Step 2 — Patient verification: Who is the patient and what examination is required?

Step 3 — Patient assessment: Can the patient safely undergo the standard examination?

Step 4 — Preparation: What communication, assistance, infection-control and equipment preparation are required?

Step 5 — Positioning: What projection will best answer the clinical question safely?

Step 6 — Technique: What exposure factors are appropriate for this patient and equipment?

Step 7 — Exposure: Apply appropriate radiation-protection measures and make the exposure.

Step 8 — Image evaluation: Does the image provide the required diagnostic information?

Step 9 — Repeat decision: Is another exposure genuinely necessary?

Step 10 — Completion: Leave the patient safely positioned and communicate or document relevant information according to local practice.

7.21 Key Principles to Remember

The radiographer should always consider:

• Why? What is the clinical indication?
• Who? Is this the correct patient and examination?
• What? What diagnostic information is required?
• How? What positioning and technique are appropriate?
• How much? What exposure is appropriate?
• Is it good enough and safe? Does the image meet diagnostic-quality criteria, and have patient, staff and environmental safety requirements been met?

7.22 Common Patient-Safety and Optimisation Errors

7.23 Key Learning Points

• Patient safety comes before achieving an ideal textbook position.
• Every examination should have a clear clinical purpose.
• Correct patient and examination identification is essential.
• Communication improves safety and image quality.
• Patient condition must influence positioning and technique.
• Accurate positioning can reduce repeat examinations.
• Appropriate exposure balances diagnostic information and radiation dose.
• Digital processing does not eliminate unnecessary radiation exposure.
• Every image should be evaluated before completing the examination whenever practical.
• Repeat imaging should be clinically justified.
• Infection prevention applies throughout the imaging workflow.
• Trauma patients should not be moved unnecessarily.
• Children and vulnerable patients require individualised approaches.
• Optimisation involves the whole examination, not just exposure factors.

7.24 Quick Reference

X-Ray Fundamentals — Master Quick Reference

1. X-Ray Tube & X-Ray Production

The anode heat-loading / cooling curve is used to understand heat storage and cooling of the X-ray tube and should be consulted to avoid exceeding tube limits.

2. X-Ray Generator & Exposure Factors

mAs = mA × exposure time

Typical exposure values are illustrative only. Equipment-specific technique charts and local protocols take precedence.

3. Exposure and Patient Factors

Patient thickness: Greater thickness generally requires technique adjustment because of increased attenuation and scatter.

Patient habitus: Exposure should be adapted to patient size and body composition.

Grid: May improve contrast by reducing scatter reaching the detector, but generally requires increased exposure.

AEC: Terminates exposure when the selected detector region receives an appropriate amount of radiation.

Exposure creep: Digital systems may produce acceptable-looking images despite excessive exposure; exposure indicators should therefore be monitored.

4. Radiographic Geometry

SOD = SID − OID

Magnification factor = SID / SOD

These relationships are simplified educational models. Actual image quality depends on the complete imaging system.

5. Inverse Square Law

Intensity ∝ 1 / distance²

Increasing the distance from the X-ray source reduces beam intensity according to the inverse-square relationship. For example, if distance doubles, intensity becomes approximately one quarter.

Important applications:

• Exposure compensation when SID changes
• Mobile radiography
• Staff radiation protection
• Understanding beam intensity

6. Radiographic Positioning Principles

Anatomical position: Standard reference position used for describing anatomy and movement.

Body planes: Sagittal, Coronal, Transverse.

Directional terminology: Anterior/posterior, Superior/inferior, Medial/lateral, Proximal/distal, Superficial/deep, Ipsilateral/contralateral.

Common patient positions: Erect, Supine, Prone, Seated, Recumbent, Lateral, Oblique, Decubitus.

Projection terminology: AP, PA, Lateral, Oblique, Axial.

Position = how the patient / body part is positioned.

Projection = the direction / path of the X-ray beam through the patient to the detector.

7. Central Ray & Positioning Geometry

• Central ray and CR perpendicularity
• Cephalic and caudal angulation
• Medial / lateral angulation
• Oblique / compound angulation
• Anatomical centring
• Detector alignment
• Part alignment
• Rotation control
• Beam divergence
• SID / OID relationship
• Appropriate breathing instructions
• Marker placement

Patient + anatomical part + detector + central ray must be aligned according to the examination objective.

8. Image Quality

Diagnostic image quality ≠ maximum image quality. The objective is sufficient image quality for the clinical task.

9. Scatter & Contrast

• Scatter reduces useful image contrast.
• Scatter increases with patient thickness and irradiated field size.
• Collimation reduces scatter production.
• Grids reduce scatter reaching the detector.
• Appropriate positioning and field restriction support both image quality and dose optimisation.

Better scatter control → improved contrast + reduced unnecessary irradiation

10. Digital Radiography

Digital Radiography Workflow

High-Yield DR Concepts

DR Cause → Effect Relationships

Digital Radiography Within X-Ray Fundamentals

Equipment: X-ray tube → generator → filtration → collimator → detector → workstation → PACS

Exposure: kVp + mA + exposure time → mAs → detector exposure → image quality / dose

Geometry: SID + OID + focal spot → magnification / unsharpness

Positioning: Patient position + detector position + central ray + collimation → anatomical demonstration

Image quality: Contrast + resolution + noise + sharpness + distortion + motion + artefacts

Digital radiography: Detector + processing + EI / DI + AEC + exposure optimisation

Radiation protection: Justification + optimisation + collimation + appropriate exposure + repeat reduction

Patient safety: Correct patient + correct examination + safe positioning + communication + image evaluation

Implementation varies according to equipment, manufacturer, local protocols and applicable regulations.

13. Radiation Protection

Justification: Should the examination be performed?

Optimisation: Can the examination provide the required diagnostic information with an appropriate exposure?

ALARA: As Low As Reasonably Achievable, while maintaining the required diagnostic information.

Time: Minimise unnecessary exposure time.

Distance: Maximise distance from the radiation source / patient whenever practical.

Shielding: Use structural or personal protective shielding where appropriate and according to current local requirements.

Collimation: Restrict the beam to the required anatomy.

Repeat reduction: Avoid unnecessary additional exposures.

14. Patient Radiation Protection

• Correct patient
• Correct examination
• Correct anatomical region
• Correct laterality
• Appropriate clinical indication
• Appropriate positioning
• Appropriate exposure factors
• Patient-size adjustment
• Appropriate collimation
• Appropriate grid / AEC use
• Exposure-index monitoring
• Avoid unnecessary repeats
• Consider relevant pregnancy issues
• Particular optimisation for children

15. Staff Radiation Protection

Primary principle: Avoid unnecessary exposure to the primary beam.

During exposure:

• Maximise distance.
• Use structural barriers where available.
• Use personal protective equipment where appropriate.
• Position yourself appropriately relative to the patient and source.
• Minimise time close to the source / patient.
• Follow local radiation-safety procedures.
• Use personal dosimetry where required.

Occupational exposure in diagnostic radiography is commonly associated with scatter from the patient.

16. Diagnostic Reference Levels

DRL = Diagnostic Reference Level.

• Used as an optimisation and monitoring tool.
• Usually based on representative examinations / patient groups.
• Helps identify unusually high or low typical practice.
• Not an individual patient dose limit.
• Values vary by examination, population, equipment and jurisdiction.

DRL ≠ patient dose limit

17. Patient Safety

Identification: Correct patient and examination.

Communication: Explain the examination and instructions clearly.

Dignity: Maintain privacy and respect.

Mobility: Assess ability to stand, sit, transfer and reposition.

Trauma: Avoid unnecessary movement and maintain precautions.

Manual handling: Use appropriate assistance and equipment.

Infection prevention: Apply appropriate hand hygiene, cleaning and PPE procedures.

Equipment: Check equipment, detector, table, supports and mobile systems.

Lines and tubes: Protect IV lines, drains, monitoring equipment and other devices.

Falls prevention: Assess risk before moving or positioning the patient.

18. Adaptation to Patient Condition

The textbook position is not always the safest position.

The radiographer should adapt examinations for:

• Trauma
• Pain
• Limited mobility
• Wheelchair users
• Frail patients
• Paediatric patients
• Bariatric patients
• Unconscious / confused patients
• Patients with disabilities
• Patients with immobilisation devices
• Critically ill patients

The diagnostic objective should be maintained as far as safely possible.

19. Image Evaluation

Anatomy: Required anatomy included.

Positioning: Correct projection and acceptable rotation.

Exposure: Adequate penetration and detector exposure.

Image quality: Acceptable contrast, resolution and noise.

Motion: No significant movement affecting diagnosis.

Distortion: Acceptable and appropriate for the examination.

Collimation: Appropriate field size.

Marker: Correct side marker and appropriate placement.

Artefacts: No significant artefact affecting interpretation.

Diagnostic adequacy: Does the image answer the clinical question?

20. Repeat Decision

Is the image diagnostic?

↓ Yes → Accept the image.

↓ No → What is wrong?

• Positioning
• Motion
• Exposure
• Collimation
• Anatomy excluded
• Artefact
• Equipment problem

Then ask: Would repeating the image materially improve diagnostic information, and can it be done safely?

Only repeat when clinically justified.

21. Integrated Radiographic Workflow

22. Core Relationships to Remember

These are general relationships. Actual effects depend on the imaging system, technique and clinical examination.

23. Essential Formulas

Where: mA = tube current, SID = source-to-image receptor distance, OID = object-to-image receptor distance, SOD = source-to-object distance.

24. High-Yield Examination Concepts

The following concepts are frequently assessed in radiography examinations and essays. Each prompts revision of the relevant full article.

• Line-focus principle
• Anode heel effect
• Bremsstrahlung vs characteristic radiation
• Tube heat loading and cooling
• kVp vs mAs
• 15% rule as an educational approximation only, not a universal technique rule
• Inverse square law
• SID / OID and magnification
• Focal spot and geometric unsharpness
• Scatter and grid
• AEC
• Exposure indicators (EI) and Deviation Index (DI)
• Exposure creep
• CR vs DR
• Direct vs indirect conversion
• DQE (Detective Quantum Efficiency)
• Histogram analysis and image processing
• DICOM / PACS
• Electronic cropping vs physical collimation
• Mobile and paediatric DR optimisation
• Contrast
• Spatial resolution
• Quantum noise
• Distortion
• Motion
• Justification
• Optimisation
• ALARA
• DRLs
• Patient identification
• Trauma modification
• Repeat / reject analysis

25. Final Master Principle

Typical exposure values are illustrative only. Equipment-specific technique charts, manufacturer recommendations, local protocols, quality-assurance requirements and applicable national regulations must always be followed.

Radiation-protection requirements, shielding practices, pregnancy procedures, dose reference levels and regulatory responsibilities may vary between jurisdictions. Applicable local legislation and professional requirements take precedence.

References & Further Reading

References are supporting sources rather than the focus of the page. For technical parameters, especially exposure factors, typical values are illustrative — equipment-specific technique charts, manufacturer recommendations, local protocols and applicable regulations should be followed.

Routine Radiography — Head & Neck

Skull AP + Lateral

Examination Overview

The AP and lateral skull projections may be performed as a projection set when an AP frontal view is appropriate for the patient's clinical condition, mobility and local examination protocol.

An AP projection is commonly used when the patient is supine on a radiographic table, trolley or bed, particularly when movement into a PA position is unsuitable. A PA and lateral set may be selected when the patient can be safely positioned facing the image receptor.

The radiographer must assess the clinical request, available history, patient condition and positioning requirements before proceeding.

In significant head trauma or suspected intracranial injury, CT may be more appropriate than routine skull radiography. The radiographer should follow the local imaging pathway and seek clinical clarification where the referral or clinical condition requires it.

1. Clinical Indications

Skull AP and lateral radiography may be requested for selected indications where plain radiography is clinically appropriate, including:

• Suspected skull fracture where plain radiography is appropriate.
• Assessment of suspected focal skull abnormality or bony lesion.
• Follow-up of a known skull abnormality where radiography is appropriate.
• Selected developmental or structural abnormalities.
• Assessment of a radiopaque foreign body.
• Other indications according to the requesting clinician and local referral criteria.

Before proceeding, the radiographer should:

• Confirm the patient's identity and requested examination.
• Review the clinical history and presenting symptoms.
• Establish that the examination is appropriate within the local referral and justification framework.
• Assess whether the patient can be positioned safely.
• Identify trauma precautions, immobilisation or other factors requiring modification of the examination.

Where the clinical information is inadequate, inconsistent or indicates that another imaging pathway may be more appropriate, the radiographer should follow the local escalation process.

2. Contraindications and Precautions

There are few absolute contraindications to a justified skull radiograph. The radiographer should consider the patient's clinical stability, ability to cooperate and whether head or neck movement is safe.

Important precautions include:

• Suspected cervical spine injury or acute head trauma.
• Existing head or cervical immobilisation.
• Reduced consciousness or inability to cooperate.
• Severe pain or restricted movement.
• Pregnancy, where applicable.
• Paediatric patients requiring adapted positioning and exposure techniques.

The examination should be modified or deferred for clarification when the required positioning cannot be achieved safely.

3. Patient Preparation

• Confirm patient identity according to local policy.
• Confirm the requested examination and clinical indication.
• Explain the procedure and the need to remain still during exposure.
• Assess the patient's mobility, pain and ability to cooperate.
• Remove radiopaque objects from the head and neck region where practical.
• Check for existing immobilisation or clinical restrictions before moving the patient.
• Prepare and review the exposure protocol, equipment settings and technical parameters before positioning the patient.
• Maintain patient dignity, privacy and comfort throughout the examination.

4. Patient Positioning

AP Skull

• Position the patient supine on the radiographic table, trolley or bed when an AP projection is required.
• An erect or seated AP position may be used where clinically appropriate.
• Align the median sagittal plane (MSP) perpendicular to the image receptor (IR).
• Position the orbitomeatal line (OML) perpendicular to the image receptor where this can be achieved safely.
• Ensure the head is not rotated or tilted.
• Centre the skull so that the entire cranial vault is included.
• A radiolucent sponge or suitable support may be placed beneath the head or chin when required to maintain alignment.
• Avoid unnecessary movement of the head or neck in trauma patients.
• For immobilised patients, adapt the projection and beam geometry according to the relevant clinical protocol.

Central ray:

• Perpendicular to the image receptor.
• Centre at the nasion for the standard AP skull projection.
• In trauma or modified positioning, follow the applicable projection protocol.

Lateral Skull

Standard erect or seated lateral

• Position the patient erect or seated when clinically appropriate.
• Place the side of the head closest to the image receptor.
• Align the median sagittal plane (MSP) parallel to the image receptor.
• Position the interpupillary line (IPL) perpendicular to the image receptor.
• Adjust the head to achieve a true lateral position without rotation or tilt.
• Use the infraorbitomeatal line (IOML) as an additional positioning reference according to the selected technique.
• A radiolucent sponge may be placed beneath the chin or another suitable location to assist in maintaining the lateral position.

Supine or trauma lateral

• For patients who cannot safely sit, stand or rotate, perform a lateral projection using a horizontal beam where indicated.
• Position the patient supine, with the head supported and immobilised as clinically appropriate.
• Place the image receptor vertically against the lateral aspect of the head.
• Align the median sagittal plane perpendicular to the table or trolley and parallel to the image receptor.
• Position the interorbital line perpendicular to the image receptor.
• A radiolucent skull pad or sponge may be used to raise and support the head so that the occipital region is included.
• The central ray should be horizontal and perpendicular to the image receptor.
• Do not remove cervical immobilisation or rotate the head unnecessarily.
• A lateral projection may be adapted for patients positioned supine or, where clinically authorised and safe, in another supported position such as prone. The patient's clinical condition and local trauma protocol determine the appropriate method.

Central ray:

• For a standard lateral projection: perpendicular to the image receptor and centred approximately 5 cm superior to the external auditory meatus (EAM).
• For a horizontal-beam trauma lateral: direct the horizontal central ray perpendicular to the vertical image receptor, with centring according to the selected trauma technique.

5. Acquisition Technique and Parameters

The following values are illustrative educational ranges. The departmental technique chart, equipment specifications, patient size, detector system and local protocol take precedence.

AP Skull

Lateral Skull

Acquisition considerations:

• Select technical factors according to patient size, skull thickness, detector response and local exposure charts.
• Use a small focal spot when tube loading permits.
• Use the appropriate grid or grid-equivalent system according to the equipment and protocol.
• Review exposure indicator or deviation index information where available.
• Remember that exposure indicators describe detector exposure and do not directly measure patient dose.
• Collimate before exposure; electronic cropping does not reduce radiation already delivered.
• Modify the technique for trauma, paediatric patients and patients with limited mobility.

6. Image Review and Quality Checks

The radiographer should review both projections before completing the examination.

AP Skull

Assess:

• Complete cranial vault included.
• Correct patient identification and anatomical marker.
• Median sagittal plane appropriately aligned.
• No significant rotation or lateral tilt.
• Appropriate orbitomeatal line alignment where achievable.
• Adequate penetration and bony detail.
• No significant motion.
• Appropriate collimation.
• No significant artefact obscuring anatomy.

Lateral Skull

Assess:

• Complete skull and skull base included.
• True lateral positioning where possible.
• Appropriate alignment of the median sagittal and interpupillary planes.
• Superimposition of relevant paired structures.
• Sella turcica demonstrated in profile.
• Adequate penetration and bony detail.
• No significant motion.
• Appropriate collimation.
• No significant artefact obscuring anatomy.

For a horizontal-beam trauma lateral, assess whether the projection adequately demonstrates the required skull anatomy while maintaining the patient's safety and existing precautions.

If an image is inadequate, identify the cause before repeating:

Positioning → centring → exposure → motion → collimation → artefact → processing

Repeat exposure should only be undertaken when clinically justified and when it is likely to improve diagnostic information.

7. Post-Procedure Care

• Confirm that the required projections are diagnostically acceptable before releasing the patient, where practical.
• Assist the patient safely from the examination position.
• Take additional care with patients who have trauma, pain, restricted mobility or altered consciousness.
• Return the patient safely to their bed, trolley, wheelchair or clinical area.
• Maintain immobilisation or other precautions until the patient is safely transferred.
• Ensure images are correctly identified and transferred to the appropriate PACS destination.
• Complete documentation according to local departmental procedures.

8. Quick Reference

AP Skull

Position

• Usually supine when AP is required.
• Median sagittal plane (MSP) perpendicular to image receptor (IR).
• Orbitomeatal line (OML) perpendicular to IR where safely achievable.
• No rotation or tilt.
• Radiolucent support may be used where required.

Central ray

• Perpendicular to IR.
• Centred at nasion.

Typical parameters

• 75–85 kVp
• Approximately 15–30 mAs
• Small focal spot
• Grid according to local protocol
• SID approximately 100–110 cm

Lateral Skull

Position

• Erect, seated or supine horizontal-beam technique according to patient condition.
• Median sagittal plane parallel to IR.
• Interpupillary line perpendicular to IR.
• True lateral position where possible.
• Radiolucent support may be used to maintain alignment.

Central ray

• Perpendicular for standard lateral.
• Horizontal and perpendicular to vertical IR for trauma lateral.
• Approximately 5 cm superior to external auditory meatus (EAM) for the standard lateral.

Typical parameters

• 75–85 kVp
• Approximately 10–25 mAs
• Small focal spot
• Grid according to local protocol
• SID approximately 100–110 cm

Radiographer's Workflow

Verify referral and clinical history → identify patient → assess clinical condition → select appropriate projection set → prepare patient → review exposure protocol and settings → position safely → centre → collimate → expose → evaluate images → repeat only when justified → complete post-procedure care → transfer images correctly.

Key principle: Skull radiography requires the radiographer to integrate clinical assessment, safe positioning, projection geometry, exposure optimisation, image evaluation and patient care. The standard position should be adapted when necessary to protect the patient while maintaining diagnostically useful imaging.

Skull PA + Lateral Views

Examination Overview

The skull posteroanterior (PA) and lateral examination is a two-projection radiographic assessment of the cranial bones. It provides frontal and lateral views of the skull and may demonstrate abnormalities involving the cranial vault, calvarium and selected intracranial bony landmarks.

The PA projection is generally preferred over the anteroposterior (AP) projection when the patient can be positioned safely because it reduces magnification of anterior cranial structures and may reduce radiation exposure to the eyes.

The lateral projection demonstrates the skull in profile and is useful for assessing the cranial vault, sella turcica and general alignment of the cranial structures.

Clinical note: Computed tomography (CT) is generally more appropriate than routine skull radiography for significant acute head trauma or suspected intracranial injury. Follow the local imaging pathway and seek clarification when the referral or clinical information is unclear.

1. Clinical Indications

Skull PA and lateral radiographs may be requested for selected clinical indications, depending on local imaging protocols.

• Assessment of suspected skull fracture in circumstances where radiography is specifically indicated.
• Investigation of focal skull abnormalities or palpable bony lesions.
• Assessment of known skull lesions or selected bone disorders.
• Follow-up of previously identified cranial bony abnormalities.
• Assessment of skull shape or cranial development in selected cases.
• Demonstration of the cranial vault and selected bony landmarks.

Routine skull radiography is not usually the first-line investigation for acute head injury, suspected intracranial haemorrhage or significant neurological symptoms.

2. Contraindications and Precautions

There are no absolute contraindications to plain skull radiography when the examination is clinically justified. Appropriate precautions are required.

• Confirm the patient's identity, examination request and relevant clinical history.
• Check whether the patient can safely sit, stand, lie prone or maintain the required head position.
• Assess pain, dizziness, reduced mobility, confusion and the risk of falling.
• In suspected cervical spine injury or significant head trauma, avoid unnecessary head and neck movement and follow the relevant trauma or immobilisation protocol.
• Do not remove a cervical collar or alter immobilisation unless authorised under the clinical protocol.
• Consider pregnancy status in accordance with local radiation protection policy.
• Remove glasses, earrings, hair accessories, dentures and other external objects that may obscure the skull, where safe and appropriate.
• Adapt positioning for patients who cannot maintain the standard position.

3. Patient Preparation

1. Explain the examination clearly and check that the patient understands the instructions.
2. Confirm patient identity using the required local identification procedure.
3. Check the referral, clinical history and requested projections.
4. Explain that the examination is quick and that the patient must remain completely still during exposure.
5. Remove radiopaque objects from the head and neck region where appropriate.
6. Prepare and review the exposure protocol, equipment settings and technical parameters before positioning the patient.
7. Position the patient according to their clinical condition, mobility and the selected projection.
8. Ensure the image receptor (IR), tube and patient are correctly aligned before exposure.

4. Patient Positioning

A. PA Skull — 0° Projection

Patient Position

• Position the patient erect, seated or prone, depending on their condition and available equipment.
• For an erect or seated examination, the patient faces the image receptor.
• For a prone examination, the patient rests the forehead and nose against the table or image receptor support, if clinically appropriate.
• Align the median sagittal plane (MSP) perpendicular to the image receptor.
• Ensure the head is not rotated or tilted.
• Adjust the head so that the orbitomeatal line (OML) is perpendicular to the image receptor, where safely achievable.
• Centre the image receptor to the expected central ray and ensure that the entire skull is included.
• Use a suitable radiolucent support if required to maintain comfortable and stable head alignment.

Central Ray and Centring

• Central ray (CR): Perpendicular to the image receptor.
• Centre to exit at the glabella for the standard PA 0° skull projection.
• Ensure the central ray is aligned with the median sagittal plane.
• Centre the image receptor to the projected central ray.

Patient Instructions

• Ask the patient to remain completely still.
• Avoid unnecessary movement of the head during positioning and exposure.
• Respiration does not normally require a specific radiographic criterion; motion control is the priority.

B. Lateral Skull

A lateral skull projection may be performed with the patient erect or seated when clinically able. A horizontal-beam lateral technique may be required for patients who are supine, immobilised or undergoing trauma assessment.

Standard Erect or Seated Lateral

• Position the patient erect or seated with the affected side of the head close to the image receptor.
• Place the median sagittal plane (MSP) parallel to the image receptor.
• Place the interpupillary line (IPL) perpendicular to the image receptor.
• Adjust the head so that there is no rotation or tilt.
• Position the infraorbitomeatal line (IOML) parallel to the front and back edges of the image receptor, where appropriate.
• Centre the image receptor to the central ray.
• Ensure that the entire skull, including the frontal, parietal, occipital and temporal regions, is included.
• A radiolucent sponge or suitable support may be used when required to maintain alignment and patient comfort.

Central Ray and Centring

• Central ray: Perpendicular to the image receptor.
• Centre approximately 5 cm superior to the external auditory meatus (EAM).
• The central ray should be perpendicular to the MSP and the image receptor.
• Ensure that the central ray is parallel to the interorbital line.

Supine Horizontal-Beam Lateral

This technique may be used for trauma patients or patients who cannot safely sit or turn.

• Keep the patient supine and maintain existing immobilisation where indicated.
• Do not elevate, rotate or reposition the patient's head if cervical spine injury has not been excluded.
• Place the image receptor vertically against the lateral aspect of the head, or use the trauma imaging arrangement specified by the local protocol.
• Position the image receptor to include the entire skull.
• Use a horizontal central ray perpendicular to the image receptor.
• Centre approximately 5 cm superior to the EAM.
• Ensure that the skull is not rotated or tilted, as far as the patient's condition and immobilisation allow.
• Follow the local trauma protocol for moving the patient, positioning the image receptor and maintaining spinal precautions.

Important: A supine horizontal-beam lateral is an established trauma adaptation. Prone or other modified positions should not be used as routine alternatives unless clinically authorised and supported by the local protocol.

5. Acquisition Technique and Parameters

The following values are educational examples rather than universal exposure settings. The local equipment-specific technique chart, automatic exposure control (AEC) system and departmental protocol take precedence.

A. PA Skull — 0°

B. Lateral Skull

6. Image Review and Quality Criteria

The radiographer should review each image before releasing the patient and determine whether the examination is diagnostically adequate.

A. PA Skull — Image Evaluation

Anatomy Demonstrated

• Frontal bone and cranial vault.
• Both sides of the skull with appropriate symmetry.
• Relevant frontal and cranial bony structures.

Positioning Criteria

• Entire skull included within the collimated field.
• No significant rotation.
• Similar distance between the lateral skull margins and the corresponding orbital regions.
• Symmetrical appearance of the cranial structures.
• Appropriate alignment of the MSP and OML.

Exposure and Image Quality

• Adequate penetration to demonstrate the cranial bones.
• Appropriate contrast and brightness for the examination.
• Sharp bony margins without significant motion blur.
• No avoidable artefacts overlying important anatomy.
• Correct patient identification and anatomical marker visible according to local policy.

B. Lateral Skull — Image Evaluation

Anatomy Demonstrated

• Entire cranial vault.
• Frontal, parietal, temporal and occipital bones.
• Sella turcica and related sellar structures.
• Skull base structures within the field of view.

Positioning Criteria

• Superimposition of the cranial halves.
• Superimposition of the orbital roofs where visible.
• Superimposition of the greater wings of the sphenoid.
• Superimposition of the mandibular rami, where applicable.
• No significant rotation or tilt.
• Entire skull included, including the frontal and occipital regions.

Exposure and Image Quality

• Adequate penetration of the skull and sellar region.
• Sharp bony margins without significant motion.
• Appropriate contrast and brightness.
• No avoidable external objects or artefacts obscuring anatomy.
• Correct side marker placed according to local policy.

7. Radiation Protection and Professional Practice

• Confirm that the examination is justified by the clinical request and local referral guidelines.
• Use accurate positioning and close collimation to avoid unnecessary exposure.
• Select exposure factors appropriate to patient size, anatomy and detector characteristics.
• Avoid repeat exposures unless there is a clear diagnostic reason.
• Use immobilisation or support only when required and ensure that it does not obscure important anatomy.
• Maintain patient dignity, communication and comfort throughout the examination.
• Document or report difficulties, modified positioning and any relevant limitations according to departmental procedure.

8. Post-Procedure Care

• Confirm that the required images are diagnostically acceptable before the patient leaves.
• Assist the patient safely from the examination position.
• Take care when mobilising patients with pain, dizziness, reduced mobility or trauma-related restrictions.
• Check that any removable supports or accessories have been removed when appropriate.
• Explain that the images will be reviewed and reported through the established clinical pathway.
• Escalate urgent clinical concerns according to local departmental policy.

9. Quick Reference

Key practice point: The patient's clinical condition takes priority over textbook positioning. When standard positioning is unsafe or impossible, adapt the examination according to the clinical request, trauma guidance and local departmental protocol.

Facial Bones

• Facial bones
• Orbits
• Nasal bones
• Mandible
• TMJ

Content under development

Paranasal Sinuses

• Routine sinus projections

Content under development

Cervical Spine

• AP
• Lateral
• Open-mouth / odontoid
• Oblique
• Cervicothoracic / cervicodorsal spine

Content under development

Routine Radiography — Chest & Thorax

Content under development

Topic Areas

• PA chest
• Lateral chest
• AP chest
• Supine chest
• Apical / lordotic chest
• Expiratory chest
• Decubitus chest
• Ribs
• Sternum

Routine Radiography — Abdomen

Content under development

Topic Areas

• AP supine abdomen
• Erect abdomen
• Decubitus abdomen
• KUB
• Acute abdomen series
• Other established routine abdominal projections

Routine Radiography — Upper Limb

Content under development

Fingers & Hand

• Fingers
• Thumb
• Hand

Wrist

• Wrist
• Scaphoid

Forearm & Elbow

• Forearm
• Elbow
• Radial head
• Olecranon

Humerus

• AP
• Lateral

Shoulder

• Shoulder
• Clavicle
• Scapula
• AC joints

Routine Radiography — Lower Limb

Content under development

Foot & Toes

• Toes
• Foot
• Calcaneus

Ankle

• AP
• Lateral
• Mortise

Tibia & Fibula

• AP
• Lateral

Knee

• AP
• Lateral
• Oblique
• Patella

Femur

• AP
• Lateral

Hip

• AP hip
• Lateral hip
• Cross-table lateral

Pelvis

• AP pelvis

Routine Radiography — Spine

Content under development

Cervical Spine

• AP
• Lateral
• Open-mouth / odontoid
• Obliques
• Cervicothoracic / cervicodorsal junction

Thoracic Spine

• AP
• Lateral

Thoracolumbar Spine

• AP
• Lateral
• Thoracolumbar junction

Lumbar Spine

• AP
• Lateral
• Obliques
• L5-S1 spot / coned view where appropriate

Lumbosacral Spine

• AP / axial
• Lateral
• L5-S1 spot / coned view
• Other appropriate supplementary views

Sacrum & Coccyx

• AP / axial
• Lateral

Sacroiliac Joints

• AP
• Oblique projections

Special / Advanced Projections — Skull & Facial Bones

Content under development

Topic Areas

• Caldwell
• Waters
• Towne
• SMV (submentovertex)
• Rhese (optic foramen)
• Other established special projections

Special / Advanced Projections — Cervical / Thoracic Spine

Content under development

Topic Areas

• Swimmer's
• Flexion
• Extension
• Other supplementary projections

Special / Advanced Projections — Shoulder

Content under development

Topic Areas

• Grashey
• Scapular Y
• Axillary variations
• Stryker notch
• West Point
• AC joint stress views

Special / Advanced Projections — Knee

Content under development

Topic Areas

• Skyline / sunrise
• Tunnel / intercondylar
• Weight-bearing
• Stress views

Special / Advanced Projections — Foot & Ankle

Content under development

Topic Areas

• Weight-bearing
• Stress views
• Special calcaneal projections

Orthopaedic / Measurement Studies

Content under development

Topic Areas

• Long-leg alignment
• Limb-length measurement
• Other established specialised orthopaedic examinations

Other Special Projections

Content under development

Detailed content for additional special projections will be developed based on internationally recognised radiography references and current clinical practice.

Principles of Trauma Radiography

Content under development

Topic Areas

• Patient stability
• Immobilisation
• Avoiding unnecessary movement
• Adaptation of routine projections
• Working around casts and splints
• Communication with clinical teams

Head & Facial Trauma

Content under development

Topic Areas

• Skull trauma
• Facial trauma
• Mandibular trauma
• Foreign-body imaging

Cervical Spine Trauma

Content under development

Topic Areas

• Immobilised patient
• Horizontal-beam lateral
• Cross-table techniques
• Trauma modifications

Chest Trauma

Content under development

Topic Areas

• Portable chest
• Rib trauma
• Pneumothorax-related imaging
• Haemothorax-related imaging
• Trauma positioning

Pelvis & Hip Trauma

Content under development

Topic Areas

• Pelvic trauma
• Suspected hip fracture
• Cross-table lateral
• Avoiding unnecessary rotation

Upper & Lower Limb Trauma

Content under development

Topic Areas

• Fractures
• Dislocations
• Casts and splints
• Adapted projections

Polytrauma

Content under development

Topic Areas

• Emergency department imaging
• Portable imaging
• Multiple injuries
• Spinal precautions
• Workflow and communication

Emergency Imaging Considerations

Content under development

Topic Areas

• Rapid image acquisition
• Patient condition versus ideal positioning
• Image quality
• Repeat decisions
• Radiation protection

Mobile Radiography Fundamentals

Content under development

Topic Areas

• Mobile X-ray equipment
• Equipment preparation
• Detector handling
• Battery / power
• Infection prevention
• Patient identification
• Communication

Ward Radiography

Content under development

Topic Areas

• Portable chest
• Portable abdomen
• Portable pelvis
• Portable extremities
• Positioning limitations

ICU Radiography

Content under development

Topic Areas

• Portable chest
• Lines and tubes
• Ventilated patients
• Supine imaging
• Image evaluation

Emergency Department

Content under development

Topic Areas

• Portable trauma imaging
• Unstable patients
• Rapid imaging

Neonatal / Special Care

Content under development

Topic Areas

• Portable chest
• Abdomen
• Lines and tubes
• Incubator imaging

Isolation / Infection-Control Situations

Content under development

Topic Areas

• Equipment protection
• Cleaning / decontamination
• Workflow

Mobile Radiation Protection

Content under development

Topic Areas

• Staff positioning
• Distance
• Scatter
• Other patients
• Clinical staff
• Mobile exposure precautions

Operating Theatre Environment

Content under development

Topic Areas

• Radiographer's role
• Theatre workflow
• Sterile / non-sterile areas
• Communication
• Infection prevention
• Equipment movement

Mobile X-Ray in Theatre

Content under development

Topic Areas

• Mobile X-ray
• Detector positioning
• Exposure considerations
• Radiation protection

C-Arm Radiography

Content under development

Topic Areas

• C-arm components
• Positioning
• AP
• Lateral
• Oblique
• Image acquisition
• Dose optimisation

Orthopaedic Procedures

Content under development

Topic Areas

• Fracture fixation
• Plates and screws
• Intramedullary nails
• Hip procedures
• Knee procedures
• Ankle / foot procedures
• Upper-limb procedures

Spine Procedures

Content under development

Topic Areas

• Cervical
• Thoracic
• Lumbar
• Instrumentation
• Intraoperative localisation

Other Surgical Procedures

Content under development

Topic Areas

• Abdominal
• Urological
• Vascular
• Foreign-body localisation
• Other established image-guided surgical procedures

Theatre Radiation Protection

Content under development

Topic Areas

• Scatter
• Staff positioning
• Distance
• Protective equipment
• Dose awareness
• Exposure optimisation

Fluoroscopy Fundamentals

Content under development

Topic Areas

• Fluoroscopy equipment
• Flat-panel detector
• Image acquisition
• Pulsed fluoroscopy
• Magnification
• Fluoroscopy time
• Dose optimisation

Upper Gastrointestinal Procedures

Content under development

Topic Areas

• Barium swallow
• Upper GI examination
• Oesophageal studies
• Small bowel follow-through

Lower Gastrointestinal Procedures

Content under development

Topic Areas

• Barium enema
• Single-contrast technique
• Double-contrast technique
• Patient preparation
• Post-procedure considerations

Genitourinary Procedures

Content under development

Topic Areas

• IVU / IVP
• Cystography
• MCU / VCUG
• Retrograde urethrogram
• Retrograde pyelography

Gynaecological Procedures

Content under development

Topic Areas

• Hysterosalpingography

Other Contrast Procedures

Content under development

Topic Areas

• Sinogram
• Fistulogram
• Sialogram
• Arthrography
• T-tube cholangiography
• Other established fluoroscopic procedures

Contrast & Patient Safety

Content under development

Topic Areas

• Patient preparation
• Contrast considerations
• Contraindications / precautions
• Adverse reactions
• Emergency preparedness
• Radiation protection

Principles of Paediatric Radiography

Content under development

Topic Areas

• Child-friendly communication
• Preparation
• Immobilisation
• Positioning
• Exposure optimisation
• Minimising repeat examinations

Neonatal Radiography

Content under development

Topic Areas

• NICU environment
• Portable chest
• Abdomen
• Lines and tubes
• Incubator imaging

Paediatric Chest

Content under development

Topic Areas

• Chest projections
• Portable imaging
• Positioning
• Breathing considerations

Paediatric Abdomen

Content under development

Topic Areas

• Supine abdomen
• Erect / decubitus where appropriate
• Acute abdomen

Paediatric Musculoskeletal

Content under development

Topic Areas

• Upper limb
• Lower limb
• Pelvis
• Spine
• Trauma

Paediatric Skull & Facial Imaging

Content under development

Topic Areas

• Skull
• Facial bones
• Other clinically appropriate examinations

Radiation Protection in Children

Content under development

Topic Areas

• Justification
• Optimisation
• Exposure selection
• Collimation
• Avoiding repeat exposures