The Radiation Protection Advisor (RPA)

The RPA is someone from outside the practice appointed by the practice to ensure that the practice complies with IRR17. This person must have specialist qualifications and have relevant veterinary experience [2].

The Radiation Protection Supervisor (RPS)

The RPS is a person/s appointed to ensure compliance with the IRRs regarding work carried out in an area subject to the local rules. In particular, supervising the safe working arrangements set out in the local rules. Suitability for appointment depends on a knowledge and understanding of the regulations, the local rules and the ability to exercise a supervisory role. People taking on the RPS role should be adequately trained by attending a certificated training course and attending refresher training as required.

These team members will work together to produce risk assessments that identify the risks when performing specific procedures such as radiography, CT and scintigraphy. They will also work together to create a set of local rules that should be displayed in all areas of practice where radiation is used, and they should be specific to that area; according to the HSE, local rules should include the following [2]:

1. The dose investigation level specified in the regulations.
   
2. Identification or summary of any contingency arrangements indicating the reasonably foreseeable accidents that are possible in practice.
   
3. Name(s) of the appointed RPS(s).
   
4. The identification and description of the area covered, with details of its designation.
   
5. A summary of the working instructions appropriate to the radiological risk associated with the source and operations involved, including the written arrangements relating to non‐classified persons entering or working in controlled areas.
   
6. Where an employer has detailed written working instructions contained within operations manuals or work protocols, it will usually be sufficient for the local rules to refer to the relevant sections of these documents. However, the employer must make sure the way these are summarised in the local rules is adequate.

Local Rules

Local rules in relation to radiation typically refer to regulations, guidelines, or protocols established by local authorities or organisations to manage and control radiation safety within a specific jurisdiction or facility. These rules aim to ensure the safe handling, use and disposal of radioactive materials and protect individuals and the environment from potential radiation hazards. Some common aspects covered by local rules related to radiation are as follows [2]:

• Radiation protection standards: Local rules specify acceptable levels of radiation exposure for workers and the general public. These standards are typically based on national or international guidelines, such as those set by the International Commission on Radiological Protection (ICRP) or relevant regulatory agencies.
  
• Licensing and permitting: Local rules often outline the requirements and procedures for obtaining licenses or permits to possess, use, or handle radioactive materials. These rules ensure that individuals or organisations comply with specific criteria, training and safety measures to minimise radiation risks.
  
• Radiation safety training: Local rules may require individuals working with or around radioactive materials to undergo specific radiation safety training programs. These programs provide education on radiation risks, safe handling techniques, personal protective equipment (PPE) usage and emergency procedures.
  
• Radiation monitoring and measurement: Local rules may establish requirements for regular monitoring and measurement of radiation levels in areas where radioactive materials are used or stored. This includes the use of radiation detection equipment, such as Geiger‐Muller counters or scintillation detectors, to assess radiation levels and ensure compliance with safety standards.
  
• Waste management: Local rules often address the proper management and disposal of radioactive waste materials generated from medical, industrial or research activities. These rules outline procedures for waste segregation, packaging, storage, transportation and final disposal in accordance with applicable regulations and guidelines.
  
• Emergency preparedness and response: Local rules may include protocols for responding to radiation emergencies, such as accidental spills, leaks, or overexposures. These rules establish procedures for evacuation, notification of authorities, containment of radioactive materials, decontamination and medical assistance.
  
• Inspections and enforcement: Local authorities may conduct regular inspections and audits to ensure compliance with radiation safety regulations. These inspections assess the implementation of local rules, verify the proper use of protective measures, review records and documentation, and address any identified non‐compliance issues.

It is important to note that the specific local rules regarding radiation can vary depending on the country, state or local jurisdiction. Organisations and individuals working with radioactive materials should familiarise themselves with the relevant local rules and regulations applicable to their specific location and activities. Consulting with local regulatory bodies or radiation safety experts can provide the most accurate and up‐to‐date information on local rules and compliance requirements [2].

Authorised Personnel

When managing any room that uses ionising radiation, it is important to understand which personnel can be in the room or a designated controlled area. In veterinary practice radiation, a controlled area refers to a designated space within the facility where radiation‐producing equipment is used, such as X‐ray machines or radioactive materials. This area is subject to specific regulations and safety measures to ensure the protection of personnel, patients and the public from unnecessary radiation exposure. Because a horse requires restraint as they are not always immobilised by sedation, procedures such as radiography require someone to handle the horse during the procedure. In practice, this would ideally be a trained member of staff such as a groom or a patient care assistant (PCA). In an ambulatory setting, the owner may be required to hold the horse. Personnel allowed in a controlled room or a controlled area must meet the following criteria [3]:

• No persons below the age of 18 may enter the controlled area.
  
• No person receiving radiotherapy may enter the controlled area.
  
• No pregnant persons may enter the controlled area.
  
• No person should operate the X‐ray equipment without the correct training and authorisation.

Room Design

Most practices will have a designated X‐ray room, which serves as the controlled area; there are specific requirements that need to be met; these include [4]:

• Floor – Dimensions should be no smaller than 1.5 m × 2 m. The control area will typically contain a viewing station. If using portable machines, this will form part of the machine.
  
• Walls – Appropriate wall protection must extend from the floor to a height of no less than 2 m. All joints should overlap alongside any necessary lead lining. Various recommended shielding for protective X‐ray room walls includes the following:
  
  
  
  • General purpose radiography and fluoroscopy – The primary wall thickness should be 320 mm solid cement before a secondary layer of 230 mm.
    
  • CT – The minimum wall thickness must be equivalent to 320 mm of concrete or a solid cement block.
  
  
• Doors – Must provide a solid barrier with lead lining necessary for radiation protection. X‐ray room doors can also include lead‐lined windows. All doors should consist of no less than 1.5 mm of protective lead.
  
• Windows – Shielded windows need to contain lead glass or lead acrylic in the form of double glazing. Window framing should be shielded with suitable lead equivalent thickness and protected by lead blinds or shutters. As for unshielded windows, positioning them at least 2 m above the ground is recommended.

As well as these features, a controlled area must be demarcated and signed using appropriate signage. A controlled area should have a two‐stage fail‐safe light in use. All doors in a controlled area should be covered. Lights must have a dual bulb system so that if one bulb were to blow, the other bulb would still work. Lights should be inspected daily. The lights should light up a yellow ‘controlled area X‐rays’ sign when the machine is switched on, and the red ‘No entry’ sign must illuminate when an exposure is taken; for this to be possible, the lights need to be wired into the X‐ray machine. If this is not possible, both lights should be illuminated at all times when the room is in use. If the portable generators are used in a yard, an area should be set up as a controlled area, and all personnel should be informed of this to prevent anyone from entering the area. To create a controlled area in a yard, the following should be carried out [5]:

• Cordon off an area of at least 2 m²; black and yellow plastic chains and bollards can be used to achieve this.
  
• Use stand‐up plastic signs that say ‘Controlled area X‐rays, No entry.’
  
• Ensure that personnel are not present in the adjoining stables; preferably, use a brick stable away from anyone else in the yard.

PPE

The use of PPE when dealing with ionising radiation is essential because, in equine practice, personnel are often present in the room when performing radiographs; the correct use of PPE is of paramount importance [3].

4.3 Lead Aprons/Gowns

Any person who is in the controlled area during exposure should wear a lead gown/apron; the minimal thickness is 0.25 mm lead equivalent. Most modern gowns will offer higher protection than this; however, this will also increase the weight of the gown. Details and considerations for 0.25 and 0.5 mm gowns are as follows [6]:

Thyroid Shields

Thyroid shields should be worn whenever a lead gown/apron is used and should be worn quite tightly. Despite a general awareness that the thyroid gland is sensitive to radiation, studies have found there are no clear protocols for thyroid shield use [3].

Dose Monitoring – Dosimeters

All those regularly involved in radiography should wear monitoring devices, and each staff member should wear at least one badge. Staff that are responsible for the daily running of radiography units may require two badges: one to monitor the whole body placed on the inside of the gown at waist height and one placed on the outside of the gown at collar height to measure thyroid exposure [5]. The practice may also place dosimeters in the radiography room or adjacent areas to monitor environmental risk to staff. All readings are documented and retained by the practice, and any high exposures should be investigated before staff are allowed back in close proximity to ionising radiation. The dosimeters must remain at the practice so that the radiation reading is accurate. Dosimeters are usually changed every three months depending on the staff member’s workload; this may be increased to monthly if at high risk. Staff should never expose themselves or others to the direct X‐ray beam or leave personal dosimeters in the controlled area if they are not present [3].

Types of Dosimeter

4.4 Real‐time Personnel Monitors

These are electronic devices that continually monitor personnel exposure and have an alarm to warn the wearer if they are being exposed to high levels of radiation. These are designed to help modify behaviours surrounding radiation safety and are starting to be used more commonly in equine practice.

All dosimeters apart from the real‐time monitors will need to be sent away for development and reading; the results are typically shared with the RPA as well as the practice.

It is worth noting that not all PPE is equal in efficacy, and the rating should be checked before use [4].

Types of Radiation

X‐rays form part of the electromagnetic spectrum along with all types of electromagnetic (EM) radiation. These radiation types are found all around us in many forms; EM radiation is energy that spreads out as it travels from its source. Figure 7.4 shows the EM spectrum and the different types of EM radiation and wavelengths [10].

Although it is strange to see radio waves and visible light in the same spectrum as X‐rays and gamma rays, they are not fundamentally different. Despite coming from various sources, they all find themselves on the EM spectrum because they are all EM radiation [11]. The different types of radiation are defined by the different amounts of energy found in the photons. Radio waves have low‐energy photos denoted by a longer wavelength, whereas gamma rays have a shorter wavelength with high‐energy photons. EM radiation can be expressed in three ways:

• Energy – Measured in electron volts
  
• Wavelength – Measured in meters (m)
  
• Frequency – Measured in cycles per second or Hertz

All three of these are precisely mathematically related [11].

Sources of Radiation

There are many sources of radiation, but these can be broken down into two different sections [10]:

• Natural sources
  
• Artificial sources

Natural Sources

Background radiation is naturally occurring and is all around us; many different sources contribute to it; these include [10]:

• Cosmic rays – the radiation that reaches the earth from space.
  
• Rocks and soils – some rocks and soils give off radiation and radioactive radon gas.
  
• Living things – plants will absorb radiation and then pass it up the food chain.
  
• Radon gas – Radon gas is a naturally occurring radioactive gas that is colourless, odourless and tasteless. It is formed from the decay of uranium, which is found in soil, rocks and water. Radon is considered a health hazard because it can accumulate in indoor environments and expose individuals to radiation.

Natural radiation levels cannot be controlled; however, they must be considered when working within veterinary medicine. The main problem that faces veterinary practice is radon gas; this naturally occurring gas emitted from the ground has been named the second largest cause of lung cancer in the United Kingdom after smoking by the HSE [12]. Practices must be aware of the radon level in their area; this information can be gathered by contacting the local authorities or searching Public Health England. Figure 7.5 shows a map of the United Kingdom and the radon risk ratings associated with each area (please note this Figure is a guide only and was compiled from information available at the time of publication; always check with authorities for up‐to‐date information).

Once armed with basic information on the local risk ratings practices, it is important to ensure that the recommended levels of 300 Bq/m³ (becquerels per cubic metre) are not exceeded [12]. If radon levels are found to be high, and the practice does not have any preventative measures in place, a test kit should be ordered and used to monitor the levels over three months; this is due to the levels fluctuating over time. If the reading comes back as low, the practice is required by the HSE to monitor the levels again every 10 years [6]. If the reading comes back as high, the practice may be required to put in place the following measures:

• Installing a damp‐proof membrane on the ground floor to provide a radon‐proof barrier [6].
  
• Complete radon protection will require provision for a subfloor depressurisation (a radon slump) or ventilation (a ventilation subfloor void) [6].

Artificial Sources

Unlike natural sources, where interventions are limited, artificial sources are sources that humans have created and now contribute to background radiation. Artificial sources now contribute to around 15% of background radiation and include [2]:

• Medical X‐rays and medical nuclear medicine
  
• Radioactive fallout from nuclear weapons testing
  
• Radioactive waste from nuclear power stations

Radioactive Emissions/Decay

There are three main types of ionising radiation; when a nuclide undergoes radioactive decay, it breaks down and falls into a lower energy state, and the energy expended is released as radiation [13]. There are three main types of ionising radiation that get emitted from an unstable radioactive atom; these are known as [10]:

• Alpha particles
  
• Beta Particles
  
• Gamma particles (or photons) [13]

Properties and Effects of Radiation

As discussed, X‐rays and gamma rays form part of the EM spectrum. All members of the EM spectrum have the following properties:

• They do not require a medium for transmission and can travel through a vacuum.
  
• They travel in straight lines.
  
• They travel at the same speed (3 × 10⁸ m/s in a vacuum).
  
• They interact with matter either by absorption or scatter [3].

X‐rays also have properties which mean in medicine, they can be utilised to image internal structures; these properties include [3]:

• The direction of travel – X‐rays will always travel in straight lines, accurately representing the patient or objects they pass through. They can only change direction if they collide with an atom, and this may degrade the image [8].

  

  
  
• Ionisation – X‐rays can interact with tissues and cause ionisation, which occurs when atoms become positively or negatively charged by gaining or losing an electron. It is this effect that allows image production and absorption; however, it is also the reason that X‐rays can damage cells and cause cancer [8].
  
• Penetration – Due to the high energy of X‐rays, they can penetrate through substances. Photon absorption depends on the nature of the substance penetrated and the energy of the photons. This means some photons will pass through the patient completely, depending on the wavelength; the shorter this is, the higher the energy of the photons [3].
  
• Divergence – As the X‐ray beam travels from the target, it will lose intensity and spread out, following the inverse square law (see below for more detail on inverse square law). This is used in radiation protection to reduce the risk and should be considered when setting up safe areas, and the focal film distance (FFD) to ensure consistent radiographs and safety has been considered [8].
  
• Absorption – As the X‐rays pass through the patient, they may be stopped or slowed by the patient’s tissue; if a dense tissue is being radiographed, for example, bone, the X‐rays will be stopped; the term radiopaque is used to describe this. If an area of less density is being radiographed, for example, the sinus, the X‐rays will not be stopped, and the term radiolucent is used. Figure 7.7 shows the different tissue types and the number of X‐rays absorbed when X‐rays pass through them. This image also shows what colour will show up on the image to denote these different tissues [8].
  
• Photographic effect – X‐rays interact with the silver halides within the X‐ray film to form an image. They also cause certain phosphors to emit light or fluoresce, the principle used in intensifying screens. The more X‐rays that strike the silver halide crystals within the radiographic film, the greater the reaction and the whiter the appearance on the processed radiograph. This interaction is also used in some types of personnel dosimeters [8].

The inverse square law is a fundamental principle in physics that describes how the intensity or strength of a physical quantity decreases with distance. It states that the intensity of a physical quantity is inversely proportional to the square of the distance from the source.

Here are the key points to understand about the inverse square law:

• Relationship: According to the inverse square law, if the distance from a source is doubled, the intensity of the physical quantity decreases to one‐fourth (1/2²) of its original value. Similarly, if the distance is tripled, the intensity decreases to one‐ninth (1/3²) of its original value and so on.
  
• Mathematical Formulation: Mathematically, the inverse square law can be expressed as:
  
• Intensity ∝ 1/distance²
  
• Where ‘Intensity’ represents the measured quantity, and ‘distance’ refers to the distance from the source.

Examples: The inverse square law is applicable to various physical phenomena, including:

• Gravity: The gravitational force between two objects follows the inverse square law. As the distance between two masses increases, the gravitational force between them decreases proportionally.
  
• Light intensity: The intensity of light from a point source, such as a light bulb or a star, decreases with distance according to the inverse square law. This explains why objects appear dimmer as they move farther away from a light source.
  
• Electric and magnetic fields: The strength of electric and magnetic fields around a point charge or a current‐carrying wire follows the inverse square law. As the distance from the source increases, the electric or magnetic field strength decreases.
  
• Application in radiological sciences: The inverse square law is particularly relevant in radiation safety and radiological sciences. It helps to determine the relationship between distance and radiation exposure. As an individual moves farther away from a radiation source, the exposure decreases in proportion to the square of the distance.

Understanding the inverse square law is important in various fields of science and engineering, including physics, astronomy, optics, radiation safety and wireless communication. It provides a fundamental understanding of how the intensity of a physical quantity changes with distance from a source

X‐rays can produce biological changes in living tissue by altering the structure of atoms or molecules or causing chemical reactions. Although this can be used as a benefit, i.e. during cancer treatments, it can also cause harm to living tissue. Therefore, radiation safety should always be considered [3]. For more information on health and safety and PPE, see Section 7.1. Understanding the dangers surrounding the use of radiation can be difficult due to several factors:

• It is invisible.
  
• It is painless.
  
• It has cumulative effects.
  
• It has latent effects which may manifest at a later time.

The results of radiation on the human body can be split into two categories:

• Somatic: The somatic effects of radiation are seen on tissue immediately after exposure to a high dose (dose‐dependent) of radiation. However, a low regular dose of radiation will have an accumulative effect, and any side effects may not be apparent for many years. The radiation harms rapidly dividing cells, meaning the most common body systems affected are the skin, gastrointestinal and reproductive systems.
  
• Genetic: The genetic effect is an effect that causes mutations in the chromosomes of germ cells in the ovaries and testes, affecting the offspring of the horse exposed.

Scatter Radiation

Scattered radiation or ‘scatter’ is a type of secondary radiation; as the primary beam leaves the tube head, the photons start to lose energy; as they interact with matter, they change direction instead of being absorbed. Each time scatter radiation hits an object, it changes direction. Not only does this have the potential to affect the image quality, but excess scatter also poses a risk to human health. Due to most equine practices using digital radiography, the detrimental effects to the image are not as readily seen as when using film; however, this should not mean that scatter radiation precautions to minimise it are not taken seriously. Scatter is produced for a number of different reasons. The following factors will alter the amount produced [2]:

• As the region under investigation gets denser – i.e. the patient’s cervical spine there is more chance for the X‐rays to interact with the electrons within the patient and result in scatter.
  
• If the collimator is not used effectively – the more open the collimator head is when the image is produced, the more chance there is to create scatter radiation. Making sure that images are collimated tightly not only benefits the image but also improves the safety of personnel. This is achieved through a collimator or light beam diaphragm, usually on the tube head mounting. This is constructed of a box containing a series of mirrors and a light source. The mirrors and light allow a beam of light to be projected onto the patient, representing the primary beam’s area and position. The area of the primary beam can be adjusted using the collimator dials located on the top and/or the side of the collimator head. It is essential if this area gets knocked that, the collimation might be knocked out of alignment, causing the light to be misaligned from the primary beam.
  
• Higher voltages – The voltage should only be increased as the body part being imaged requires; the more energy used to produce an image, the more chance that the scatter will reach the plate; this could cause fogging on the plate (this is not seen as much in digital radiographs, but it can indicate an overexposed image).

Scatter radiation should be controlled to minimise the effect on the radiograph and ensure that staff are not exposed to any unnecessary harm. This can be done in several different ways [4]:

• If the structure that is being radiographed is dense, such as the shoulder, the limb can be manipulated, i.e. have a handler pull the limb forwards; this will bring the leg out, away from the body and reduce the amount of tissue that needs to be penetrated.
  
• Collimation of the primary beam will reduce the area exposed to radiation, improving safety and reducing tissue exposure and scatter. Collimation will enhance the quality and contrast of the image.
  
• Reducing the voltage as much as possible while achieving a diagnostic image.

As well as reducing the amount of scatter radiation produced, it is essential to reduce the amount reaching the film, as this will decrease image quality. Using a grid can be an effective tool to aid with this [6]. Depending on the type, a grid can remove 85–95% of all scattered radiation. A grid is constructed of alternating strips of a material able to absorb radiation, for example, lead. The gap between these strips (interspace) is made with a radiolucent material, usually aluminium or carbon plastic fibres. The interspace allows the primary beam to pass through to the film. However, the lead strips absorb the scatter radiation that does not hit the X‐ray panel in a parallel orientation. Every grid has a grid ratio, which is determined by the lead strips’ height and distance between them; this is used to calculate a grid factor. The grid factor influences the amount by which the mAs must be increased to compensate for the presence of the grid (typically, this is between 2 and 6). The introduction of digital radiography has meant that using a grid is not as necessary due to the computer’s corrective software; it may still be advisable to use a grid when using higher exposures on areas such as necks and backs [7].

Tube Structure

The tube head is responsible for producing X‐rays and is comprised of an anode and cathode surrounded by a Pyrex tube. The purpose of the tube is to create a vacuum, preventing unwanted interactions during the production of X‐rays. The anode and cathode have a high‐tension electrical supply to create the necessary direct current to generate X‐rays. Oil surrounds the Pyrex tube; this prevents the build‐up of heat, and there is a lead surround to prevent X‐rays from passing straight through the tube. Although a lead case surrounds the entire structure, a small window under the anode allows the primary beam to exit the tube. A small aluminium filter in the window removes any low‐energy X‐rays as this can be undesirable for image quality [8].

The Cathode

The negative side of the X‐ray tube head is known as the cathode, and it comprises the following elements:

• A filament
  
• A focusing cap

The filament and its supporting wires are very fine wires that are heated to produce electrons in a similar way to which a toaster heats bread. To prevent the filament from melting, it is made from tungsten, which has a high melting point of around 6192°F (3422°C). The function of the focusing cap is to channel electrons in a narrow band towards the anode during exposure [15]. Both the electrons and focusing cup are negatively charged; this allows the electrons to be relayed to the centre, ensuring they remain in a narrow stream and are not spread, which means that no electrons fall beyond the boundaries of the anode [8].

The Anode

The anode is on the positive side of the X‐ray tube and can be either stationary or rotating. As seen in Figure 7.8, the stationary anode is fixed, as the name may suggest. This type of anode is generally used in smaller portable units where a high tube current and power are not required [9].

Tubes that contain a rotating anode are used in larger, more high‐powered machines that are required to produce a high‐intensity beam quickly. Figure 7.9 shows the rotating anode in the tube head. Typically, most machines will have a rotating anode; stationary anodes are more common in small animal dental units.

The anode serves two principal functions [9]:

• It provides mechanical support for the target.
  
• It acts as a good thermal conductor for heat dissipation.

X‐ray production results in 99% heat and 1% actual X‐rays, so the heat must be removed to prevent the anode from melting. The target is the area where the electrons strike. In a rotating tube, this is a disc around the entire circle of the target disc. As the target rotates, the area that the electrons strike changes; this increases the area that the electrons can strike which in turn, increases the tube’s lifespan [8]. If the anode is stationary, the whole surface is the target. The target is made of tungsten alloy embedded in a copper anode. In some tubes, the target is supported on molybdenum or graphite to make tube rotation easier. The area hit by the electrons is called the focal spot, which is the source of the radiation emitted from the X‐ray tube. The effective focal spot emitted from the tube will alter depending on the angle of the target. This angle is usually between 7° and 20° to the vertical. The focal spot’s effective size increases as the target angle increases (Figure 7.10) [8].

Exposure Factors

When using a grid, it is essential to understand how to calculate new mAs; this can be done by using a simple grid calculation. But first, it may be necessary to work out the exposure factors [3].

Working out exposure factors can be important as some machines will work on the mA, whereas others will work on the mAs. Exposure factors can be worked out using a simple triangle calculation (Figure 7.12). Using this as a reference, try to solve the following maths questions (answers found at the end of the chapter):

Question 1:

• mAs = 10
  
• mA = 100

What are the seconds?

Answer:

Question 2:

• mA = 200
  
• S = 0.2

What is the mAs?

Answer:

Question 3:

• mAs = 20
  
• S = 0.1

What is the mA?

Answer:

Once the current and time of exposures have been worked out, it becomes easy to link the kV into the equation [6].

A simple rule links kV and mAs:

• Increasing the kV by 10 allows the mAs to be halved
  
• Decreasing the kV by 10 requires mAs to be doubled

Question 4:

• kV = 50
  
• mAs = 24
  
• The kV is changed to 60

What is the new mAs?

Question 5:

• kV = 40
  
• mAs = 12
  
• The kV is changed to 30

What is the new mAs?

Adding a grid:

The equation used for using a grid is:

Question 6:

• Old mAs = 12
  
• Grid factor = 3

What is the new mAs?

Parallel Type Grids

A grid where the absorbing strips are parallel to each other in their longitudinal axis. Also known as a non‐focused linear grid, it has parallel strips when viewed in cross‐section; this is why it is called a parallel grid [9].

Focused Type Grids

A grid in which the absorbing strips are slightly angled towards the focal spot. The grid can therefore be used only at a specified focal distance. Otherwise, the grid will absorb the primary radiation, and parts of the film are barely exposed. Focused grids may be linear or crossed [9].

Criss‐cross Type Grids

A grid consisting of two superimposed parallel grids having the same focusing distance. Such grids efficiently remove scattered radiation but must be arranged at precisely right angles to the beam; this is, therefore, the limiting feature of these grids [9].

Tapered Type Grids

A grid in which the surface is tapered into the centre of the grid, functioning similarly to a focused grid. All of the strips are parallel to each other, and the tapered surface is towards the focal spot [17]. Figure 7.13 illustrates the different layouts of stationary grids.

Mobile grids, also known as ‘Potter‐Bucky’, move during exposure and are integrated into an X‐ray table, moving rapidly from side to side. The chance of grid lines can be eliminated when using a mobile grid. Due to this type of grid requiring a table and motor, this is not practical in equine practice [8].

Portable

Portable generators are the most common in equine practice; they are convenient to fit into cars in their protective case and powerful enough to take good‐quality radiographs. Modern portable generators are battery‐powered, making it possible to radiograph a patient in a variety of situations. Older systems may still rely on a power cable, which limits their use to yards with a power supply. Due to their size and relatively low power, they are best suited to imaging lower limbs. However, some more modern units have increased in capacity, making it possible to image more proximal structures (it is important to remember that this can affect image quality as the exposure time is also higher, making it easier to get movement blur). Figure 7.14 shows a battery‐powered portable generator currently on the market.

These generators should always be used with a stand. This statement from the HSE should be considered when using stands:

Here is a message from the community manager:

It has been brought to the attention of HSE’s Radiation Team that it has become common practice to carry out certain equine X‐ray radiography examinations with the vet, or other person, holding the X‐ray device. HSE are firmly of the opinion that it is reasonably practicable to use a stand or holder for the X‐ray device for these types of exposures. Furthermore, an attempted justification that holding the X‐ray device ‘saves time and money or it’s just easier’ is simply not acceptable.

Holding an X‐ray head/tube means that radiation exposures to the person holding it would not be As Low As Reasonably Practicable [ALARP] and there may also be a risk of serious, or fatal, electric shock. Additionally, there is the added risk of being very close to the horse if it were to kick out or move suddenly. In most cases HSE Radiation Specialist Inspectors will prohibit this practice if they become aware of it during an inspection, unless there was a very robust justification and it was fully considered in the radiation risk assessment with detailed safe systems of work in place [2].

Therefore, hand‐holding of the X‐ray generator poses an unacceptable risk to the personnel involved from the standpoint of radiation safety. Because of this, many different types of generator stands are available on the market that can suit individual practice needs and prices. Figure 7.15 shows the Stat‐X Espléndido sold by Podoblock; these stands are versatile and easy to use [18].

Mobile

These generators are rarely used in equine practice as they are bulky and have low ground clearance; historically, they were helpful in the operating theatre as they have a higher‐powered output and were better for the radiographic examination of the pelvis and intraoperative radiographs during fracture repair as the older portable machines had wires that could get in the way of the sterile field [7]. However, they have now largely been superseded by battery‐operated portable units as the limitations of these machines outweigh the positives. Besides the poor manoeuvrability that this type of machine offers, it is also impossible to have the tube head reach the floor in most models, meaning it would be impossible to radiograph the horse’s feet. These units are primarily used in human trauma units where moving the patient could cause further damage, and speed is essential. Figure 7.16 shows a modern DR mobile X‐ray generator.

Fixed or Static

Fixed, sometimes known as static generators, are commonly used in equine referral practices and larger first‐opinion practices. These high‐output generators generally produce higher kVp (kilovoltage peak) and mAs compared with most portable machines. It is essential that the maximum kVp and mA are understood if using X‐ray generators; this can be found in the technical specifications of the product. Figure 7.17 shows a gantry‐mounted fixed generator [3].

CR Systems

Unlike traditional X‐ray systems, which use film, CR systems use photostimulable phosphor imaging plates to capture images. Upon radiation exposure, the plate captures an image of the patient, which is CR’s main similarity to traditional X‐ray film capture. Instead of going through darkroom processing, the CR system uploads the image to a computer program for analysis [20]. This program allows the image to be adjusted and apply digital enhancements to make analysis easier.

Computed radiography systems comprise several hardware and software components that perform each part of the imaging process.

The main parts of a CR system include [21]:

• Radiographic generator: This device emits the necessary radiation to create an image on the plate.
  
• Imaging plates: CR systems use cassettes containing reusable phosphor plates rather than film. These can be erased and reused these plates thousands of times, significantly reducing the need for consumables.
  
• Image labeller: This labels the image with the correct patient details and views before processing; it is often connected to the workstation.
  
• Image reader or processor: The reader replaces the darkroom of conventional X‐ray development. Rather than applying chemical solutions to an exposure to reveal the image, CR readers scan the phosphor plate and digitise the image. They then transfer the image to the workstation.
  
• Workstation: Most CR radiography systems use a standard PC to view, evaluate and send digitised images.
  
• Software: Diagnostic imaging software provides a consolidated platform for storing, analysing and managing radiographs. This software streamlines file management and optimises analysis processes.

Proper system maintenance is critical for ensuring high‐quality radiographs. For example, imaging plates must be erased after each use because residual energy can create ghost images in later exposures [15]. It is also essential to regularly erase unused cassettes, which can capture faint images even while not in use. CR cassettes need cleaning regularly (this should be done following the manufacturer’s guidelines).

The CR Process

CR can be misleading because the imaging process includes minimal computations. It is more similar to traditional X‐ray imaging than most computer processes [21].

The process works as follows:

1. Exposure
   

   First, using a generator, expose the imaging cassette and patient to radiation to capture a latent image. The energy from the radiation remains trapped in the cassette’s phosphor layer [21].

   
   

   Exposure time and image quality can vary depending on the type of cassette used and other factors such as software, FFD, kV and mAs and the monitor used for viewing.

   
   
2. Labelling
   

   The cassette is then placed into a labeller that applies the patient details and view to the final computed image [21].

   
   
3. Digitisation
   

   The cassette is then placed into the CR reader, which scans the plate using a focused laser beam. The plate emits a bright blue light in response, allowing the reader to pick up the image on the plate [21].

   
   

   Using an analogue‐to‐digital converter (ADC), the scanner turns the light into a digital signal that transfers to the computer. Then, it wipes the image from the plate using a high‐intensity light source [21].

   
   
4. Analysis
   

   Analysis can begin once the converter has transferred the image to the workstation. The computer software allows image manipulation for more in‐depth analysis. The cassette can be reused immediately after erasure if needed [21].

DR Systems

Flat panel detectors have become the modern favourite for X‐ray imaging detecting systems. The reason can be attributed to its numerous benefits over other image‐detecting systems, including image intensifiers and X‐ray film plates [16].

The flat‐panel detector is a modular composition of individual functioning units that combine to make detecting X‐rays possible. These functional units are known as pixel arrays and are used to convert X‐ray radiation to light energy, making up the image. These pixel arrays are the sensitive parts of the flat panel detector, which are usually square or rectangular shapes with varying dimensions depending on the size of the sample material under examination. However, depending on the desired spatial resolution, this array may include thousands of pixels, with each pixel having square shapes and micrometre‐long sides. For every functional unit of the flat panel detector, very short radiation falls on the pixel array whenever an X‐ray image is taken, while the pixels collect and store this radiation until it is read out. These pixels each include a photodiode that uses the impacting X‐rays to generate an electrical charge. The pixels also have a switch with a thin‐film transistor (TFT) or indium gallium zinc oxide (IGZO), often utilised as a display technology. However, IGZO is a more recent advancement than the TFT. The switch and the photodiode help generate the image by direct or indirect conversion of the X‐rays [16].

Flat Panel Detector Working Principle

Generally, detectors are classified based on their method of conversion of X‐rays to light energy during the creation of the image. According to this definition, two types of detectors, direct and indirect, are used in flat panel detectors [16].

Direct Detectors

The type of X‐ray conversion used in direct detectors is the direct conversion method from which they derive their name. They establish their transformation using photoconductors like amorphous selenium (a‐Se) or similar photoconductors to convert X‐ray energies to an electric charge directly. Electron hole pairs are generated from the X‐ray photons on the selenium layer using an internal photoelectric effect. Applying a bias voltage to the selenium layer depth allows the holes and electrons to be drawn to corresponding electrodes to generate a proportionate electric current to the radiation’s intensity. In the TFT, array an electronic device is employed to read out the signals [16].

Indirect Detectors

Indirect detectors, on the other hand, employ a scintillating material layer such as gadolinium oxysulfide or caesium iodide to convert the X‐ray energy to light with an amorphous silicon detector array embedded behind the scintillating layer. Like the image sensor chips found in a digital camera, photodiodes are included in every pixel that produces the electrical signals. These signals are comparable to the scintillator layer lights in front of the pixels used to generate a precise X‐ray image [16].

Flat Panel Detector Process

To generate the images after an X‐ray examination, the X‐rays are converted into light energies that are also converted into electrical signals for each pixel’s photodiodes. Furthermore, a thin‐film transistor switch enables the readout of the electrical signals of each diode. Also, the photodiode and TFTs switch are connected using a signal wire with either an analogue or a digital conversion to generate an image after a low‐noise amplification [22].

Image Quality

Image quality is a main parameter that influences the diagnostic success of an imaging procedure. The quality of the image is vital to ensure a correct diagnosis and avoid misinterpretation of an image. This is especially important concept to consider as registered veterinary nurses (RVNs) may be directed to acquire images for the veterinary surgeons (vets) to assess at a different time. Table 7.2 displays the different parameters that influence image quality [13].

Methods of Restraint for Radiographic Examination

The restraint of equine patients in preparation for radiographic examination is performed in two ways: manual and chemical. Special consideration needs to be given to manual restraint as this means radiation exposure for more personnel, and under IRR17, this should be limited where possible. Some patients cannot be chemically restrained due to the type of radiograph, for example, a barium swallow. However, most patients will be given a sedative to achieve chemical restraint; the correct restraint is essential to minimise the chances of injury to the horse or personnel during exposure and any damage to expensive equipment [9]. It is the responsibility of the case vet to assess the need for sedation and if required, to prescribe the correct type and dose of sedation to be administered.

When imaging patients with debilitating conditions, clinical considerations are essential to avoid causing a deterioration in the condition of the horse. Pain and suffering must be avoided as much as possible. With these patients, depending on the area of interest, it may be helpful to use nerve or joint blocks to assist with good radiographic technique. This decision would be made by the case vet.

The implications of poor patient positioning can be detrimental to the diagnosis and therefore the prognosis of an injury. The best radiographic outcome can be achieved by ensuring the following [9]:

• There should be enough personnel available to carry out the procedure safely. Ideally, this should include a horse holder, a plate holder and a radiographer.
  
• The patient should be correctly restrained by a handler wearing appropriate PPE.
  
• The patient should be standing square, on a level surface.
  
• There should be enough room to manoeuvre around the patient with the radiographic equipment.

Figure 7.18 shows a horse positioned ready for a radiograph.

Radiographic Views

When radiographing a horse, the RVN must understand the requirements of the images to be captured. In order to achieve this, the RVN must have an understanding of anatomical projections and radiographic views. Figure 7.19 Displays nomenclature used to describe anatomical and radiological views. The direction of the X‐ray beam is indicated by first describing the position of the tube in relation to the area of interest and then that of the X‐ray cassette (Figure 7.19):

• In the head and trunk, ‘left to right’ and ‘right to left’ are the correct descriptions but may be referred to as ‘lateral’ on the radiograph (Figure 7.19).
  
• Dorsoventral and ventrodorsal are straightforward (Figure 7.19).
  
• Obliques should be described by starting with the closest standard projection and then adding the angle and direction in which the projection is altered (Figure 7.20). For example, a lateral view of the cervical vertebrae with the tube head tilted down by 30° would be described as a latero‐dorsal lateroventral radiograph. In the limb, a view from the side is called a lateromedial or mediolateral. Above the carpus and tarsus, front‐to‐back views should be called craniocaudal or caudocranial. Below and including the carpus and tarsus, front‐to‐back views are called dorsopalmar or palmarodorsal in the forelimb, and dorsoplantar or plantarodorsal in the hindlimb.
  
• Obliques are constructed as described above but can be more complex.
  
• A view from between dorsal and lateral would be dorso – X° – lateral palmaromedial (Figure 7.20).

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

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  Mar 1, 2026 | Posted by admin in NURSING & ANIMAL CARE | Comments Off on Diagnostic Imaging

  

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  Parameter	Specific properties	Factors	Solutions
  Image resolution	Image resolution quantifies how close structures can be to each other and still be visibly resolved and provides a measure of detail	Conventional radiography is usually expressed as line pairs/mm (10–15 lp/mm) – this book does not cover conventional radiography as it is not a process regularly used in equine practice	An essential factor in viewing a radiograph is the viewing screen; this needs a high‐resolution screen; otherwise, the image taken as a high resolution will not be considered a high‐resolution image, which means that the image will look poor in quality and this may affect the diagnosis
  		In CR/DR radiography, the image is expressed in pixels, similar to photo cameras and smartphones	The resolution of an image is also impacted by how a file is sent; a jpeg (Joint Photographic Experts Group) which is a default setting for an image, compresses the file and reduces its quality; therefore, all diagnostic images sent to a vet should be sent as a DICOM (Digital Imaging and Communications in Medicine) image
  		The manufacturer sets image resolution, which cannot be changed in DR systems; however, different plates with different resolution types are available in CR systems. While the standard plates are sufficient for most applications, high‐resolution plates may be better for fine trabecular detail	Follow the manufacturer’s guidelines, and if purchasing a new system, make sure these details are thought about
  		In veterinary medicine, there are no minimum resolution guidelines a system needs to have; however, they typically follow the ones set for human medicine	Contact the manufacturers to help make standard exposure charts that will be suitable for equine patients. Collaboration within the practice as the units are used will also enable this to happen
  Image sharpness	Image sharpness describes how well the edges of a structure can be distinguished from other structures or the background. Image sharpness is affected by the equipment and the way radiographs are taken	Film‐focus distance (FFD): try to ensure that the FFD is between 75 and 110 cm in modern units. This is marked with a laser that forms a cross on the patient at the correct distance; failing this, most units have an inbuilt tape measure	Using a generator stand should always be done for health and safety reasons; however, it also has an impact on movement blur as the holder often moves while holding
  		Distance between the horse and the X‐ray plate: try to keep the plate as close to the horse as possible, as this reduces the magnification of the image. If using a DR flat panel, be aware that the patient kicking the plate may cause costly damage	Using a plate stand rather than holding equipment by hand is also another way to reduce exposure to personnel
  		Movement blur: movement blur can occur through all personnel involved in radiography	The use of a headstand may help steady the whole horse
  			Adequate sedation, a combination of butorphanol and detomidine or romifidine, usually works well – over sedation is also undesirable, though, as this will increase movement blur
  			Exposure time should be as short as possible; however, this can be difficult in the smaller output machines radiographing denser tissues such as the neck and back. Where possible, try to keep exposure time below 0.2 s
  			Post‐processing: many systems have edge enhancement options. Beware that these can also lead to a false impression of sharpness
  			Collimation: generally, the tighter an image is collimated, the sharper the image will be – however, it is essential to read the manufacturer’s guidelines as this may not be the case with a DR system
  Image contrast	Image contrast is the difference in radiodensity that makes an object distinguishable from another structure	The pixel depth (in bits per pixel) measures the image’s contrast resolution (grey value). For example, a 1‐bit image shows only black and white, an 8‐bit image shows 256 greys and a 12‐bit image 4096 greys It is expressed as contrast resolution and is a measure of the grey values. The more ‘greys’ an image displays, the more structures of different radiodensities it can distinguish	Image processing: DR and CR systems offer many post‐processing and viewing options; good understanding and practical training are essential in getting the most out of a system
  			Image display: ensure that the viewing screen has an adequate contrast range. When viewing an image, changing contrast and brightness will often facilitate a more accurate appraisal of the image
  			Detector: different systems have different contrast, and this should be considered when buying a new system
  			Object: size and radiodensity; this is obviously out of the control of the operator
  Signal‐to‐noise ratio	The signal‐to‐noise ratio is the ratio between the wanted information (for example, the image of a bone) and unwanted interference ‘noise’ (anything that hinders us from seeing the bone clearly)	Scatter: in the horse, the primary factor causing ‘noise’ in an image is scatter radiation, which is in turn influenced by the amount and radiodensity of the tissues. This is especially a problem in the proximal area of the horse	Collimation: the easiest way to decrease scatter is to collimate around the area of interest as tightly as possible
  			Exposure values need to be set correctly using as low as reasonably possible (ALARP) protocols
  			Detector and post‐processing system: some systems are more sensitive to scatter than others
  			Filter: this can be in the form of mechanical grids or digital filters. Grids can be used to reduce scatter to a certain degree. DR systems often reach the same scatter reduction as a grid through inbuilt filters. Grids need to be carefully chosen for the system used and require perfect alignment of the beam and an exact distance between the grid and the X‐ray machine (required distance is usually shown on a label on the grid)
  Exposures	Three parameters determine radiation exposure: kVp (peak kilovoltage), mA (milliamperes) and time (seconds)	kVp determines the energy of the X‐ray beam and its penetration ‘power’	Decreasing the kVp settings increases the image contrast and decreases the latitude. A kVp setting under 70 is desirable for good bone radiographs. The higher the kVp, the lower the contrast and the more scatter is generated