Veterinary X-ray practices

In veterinary X-ray practices, the risks caused by radiation can be kept very low. In X-ray imaging, radiation is produced momentarily during the imaging.  

Typically, imaging is performed in a separate imaging room, which is designed so that practically no radiation leaves the room.  Where possible, the animal is sedated and positioned using, for example, sandbags, foam wedges and other holding aids. In this way, people do not need to be in the room during the imaging. If it is necessary to hold the animal during the imaging, the owner of the animal can be the holder. Then, the radiation exposure of the worker undergoing more frequent imaging situations is reduced. In any case, radiation protection aspects and adequate radiation shielding must always be considered. For example, a person who is under the age of 18 or pregnant cannot be the holder.

If you must be in the imaging room during the imaging, the majority of the exposure is due to radiation scattering from the animal. When imaging with a conventional X-ray equipment, a dose of 1–10 µSv may be caused to the holder by a single imaging if no radiation shields are used. During the use of radiation, the lead-rubber protective aprons, coats or gloves of persons working near the animal and the protective equivalent should be at least 0.5 mm. In this case, the shield limits the radiation transmission through the shield to less than 5%, which significantly reduces the effective dose to the worker.

In addition, exposure can be significantly reduced, for example by:

• increasing the distance to the animal being imagined (doubling the distance reduces worker exposure to approximately a quarter)

  • if the image receptor cannot be placed on the imaging table or on a separate rack, for example, when imaging a horse, it is advisable to use a holder with an arm.

• using as small a field size as possible for the examination

• by reducing the imaging values (imaging voltage and current).

If imaging is performed in an open space or outside the actual imaging room, for example, in horse stables, the need for radiation protection has typically not been taken into account when designing the space. In this case, it must be ensured that there are no outsiders in the vicinity of the equipment and the animal during imaging. For example, when operating in an open area, there should be plenty of space in the direction of the radiation beam where you are not allowed to stay during imaging. If possible, X-rays should be taken towards a load-bearing stone wall, as it is a structurally strong wall with a protection capacity better than that of other walls.

Assessment of radiation exposure resulting from the practice

In general, the exposure caused to workers in veterinary x-ray practices remains significantly below the limit 1 mSv, above which the worker should be classified as a radiation worker. The amount of exposure is significantly affected by the number of X-rays taken and the radiation shields used. However, the annual exposure may approach the limit of 1 mSv if the worker often must work in the imaging room during imaging or if the imaging is carried out in an open space where there is no possibility to keep distance to the subject of the imaging. In this case, the operator must arrange monitoring of the exposure conditions, for example, by means of a group dosemeter, and, if necessary, categorize the workers as radiation workers.

When the practices are reasonably planned, the occupational exposure and exposure to the population in veterinary X-ray practices is low. The effective dose typically caused by veterinary X-ray practices to workers per year is less than 1 mSv and to members of the public less than 0.1 mSv. In both cases, the classification of radiation practices related to the safety assessment of radiation practices is 3, i.e. the smallest possible. 

Chief of Radiation Safety and the use of Radiation Specialists

In veterinary X-ray practices, the Radiation Safety Officer is a veterinarian or a radiographer who has completed appropriate training, or a hospital physicist. Suitable areas of training include veterinary X-ray practices, native X-ray practices and the general use of radiation in health care and veterinary medicine.

If the practices are classified in both occupational exposure and exposure to the population, category 3, a Radiation Safety Expert must be used, if necessary, during the practices. Typically, the need to use a Radiation Safety Expert arises if there are major changes in practices or operating methods. This may happen, for example, during the commissioning of new type of equipment or during a change of the imaging location.

When the practices begin, a Radiation Safety Expert must also be used to assess the radiation exposure to workers and members of the public. The Radiation Safety Expert helps, for example, in the designing of premises and the commencement of practices and in other practical matters related to radiation protection.

Radiation safety deviations

A single radiation safety deviation in veterinary X-ray practices usually results in a relatively small additional radiation exposure. However, when planning the practices, it is important to identify situations in which unnecessary exposure may occur and to try to proactively prevent deviations. A radiation safety deviation occurring in connection with a veterinary X-ray examination is typically related to the fact that there is an external person in the imaging situation or in the vicinity, one of the participants does not use radiation protection appropriately, the hands of the holder of the animal are in the imaging area or the equipment is not working optimally.  

It is important to address the radiation safety deviations that have occurred and to take the necessary measures to prevent them in the future. If necessary, a Radiation Safety Expert may be used to assist in determining the radiation exposure caused.  

If a radiation safety deviation occurs in veterinary X-ray practices, it is typically not necessary to immediately report it to STUK. However, an example of a radiation safety deviation that must be reported to STUK without delay is a theft or loss of a radiation appliance or a technical failure of the appliance that systematically causes additional exposure.

A quality assurance programme must be prepared for radiation practices. The program sets out the quality assurance measures, their performance guidelines, the reference limits and the actions to be taken if they are exceeded as well as the responsibilities for the implementation of the program's measures. The results of the quality assurance measures must be documented. In veterinary X-ray practices, quality assurance covers the condition and mechanical function of the X-ray equipment as well as the condition of emergency switches, warning lights and radiation shields (checked at least annually). The quality of these can usually be confirmed without any special equipment. Instructions for performing these tests can be found in the following sections.

In addition, the technical performance of the X-ray equipment must be verified at least every 36 months.  An exception to this is intraoral X-ray equipment for which no specific interval for operational tests has been defined. Faults and deficiencies affecting radiation safety must be repaired before using the equipment. Records of equipment faults, repairs made and other events affecting radiation safety must be kept. Ensuring the functionality of the equipment requires special technical expertise and special equipment, such as radiation meters and quality control phantoms. Therefore, the verification is usually done by the equipment supplier's maintenance service or other maintenance service.  

The frequency of use of the equipment, among other things, should be taken into account in the inspection interval. The operability of the X-ray equipment must be verified after significant maintenance or repair, for example, and always if there is reason to suspect changes in the operation of the equipment.

Acceptance inspection and commissioning of X-ray equipment

The instructions and other documents related to the use of the equipment must be provided with the equipment. For example, the user manual, technical manual, installation manual and other possible documents are integral parts of the equipment. If there are shortcomings in the instructions and documents of the equipment, the delivered equipment can be considered to be incomplete. The manuals must also correspond to the supplied hardware and software versions.  

X-ray equipment must undergo an acceptance inspection before it is actually put into operation. The operator is responsible for ensuring that the acceptance inspection has been carried out, but usually the inspection is carried out by the supplier. The acceptance inspection ensures, among other things, that the equipment functions appropriately and safely after the transport and installation so that the statutory requirements and the key performance and safety characteristics stated by the manufacturer are met. Issues being inspected include, for example, the accuracy of the radiation beam and alignment light as well as inspections of the radiation output characteristics, such as the accuracy, repeatability and linearity of the tube voltage (KVp), tube current (mA) and imaging time (s). During the acceptance inspection, the reference performance value for the performance of the equipment is also determined.

The supplier often organizes user training, the scope and timing of which should be determined already when purchasing the equipment. In the training, special attention must be paid to the new features of the equipment and the features that have changed compared to any previous equipment. Changes may have been made, for example, to the general equipment safety and the ratio of imaging parameters to the sensitivity of the imaging receptor.

It may be sufficient for the acceptance inspection of mobile X-ray equipment that the equipment undergoes the tests deemed necessary by the operator before it is put into service. This applies to situations where compliance with the acceptability criteria during the use of the equipment has been appropriately ensured.

Checking the mechanical functioning of X-ray equipment

The mechanical functioning and condition of the X-ray equipment should be monitored continuously when using the equipment. For example, the persistence and centering of the orientation or positioning of the X-ray tube and the condition of the cables of the equipment should be monitored in normal imaging situations. The operation of any emergency switches and warning lights must be checked by testing.

Inspecting radiation and light field

The radiation and light fields can be inspected by taking an X-ray of the metal signs at the corners of the light field (for example, coins). The edges of the beam are compared with signs indicating the corresponding edges of the light field, and it is checked that the difference between them is not more than 1 cm or 1% of the distance between the focus of the X-ray tube and the imaging receptor.

Inspecting the condition of protective radiation shields

When radiation shields are stored in places reserved for them, for example, in racks intended for radiation shields, the shields will retain their shape and their maximum service life. The condition of radiation shields can be verified first by checking any damage manually and visually. This ensures that the protective material has remained in place. It is also checked whether the cover fabric and seams of the radiation shields are intact. If necessary, the condition of the protective shields can be verified by imaging. New protective shields may also be X-rayed to ensure that the protective shielding is in good condition at the time of purchase and that the protective material has not been fractured or worn. The X-ray should be taken without a grid, as the grid may interfere with its interpretation. When interpreting the image, it is worth noting that the image may be slightly wavy, in which case the image will show small greyscale discrepancies.  Small holes may also appear in the seams, but they are covered when the shield is worn.

Recommendation on image viewing environment and image monitor quality control

The operation of the image monitors should be assessed with the help of possible test images and programs on the image viewing workstation. Test images can be used to check that the monitor meets the specifications promised by the device manufacturer. By comparing the results of the assessment with the previous results, it is possible to see if the monitor features have changed and impaired its performance.  

The viewing conditions of the image are linked to the lighting of the room, and it is important to pay attention to the reflections visible on the screen of the monitor. The viewing conditions can be checked by paying attention to the position of the monitor and the viewing angle. For example, the monitor must not show reflections of light sources when viewing a dark or black screen. The room should also be dim enough for viewing X-rays so that contrast differences in dark areas can be observed.  

For the purpose of a weekly inspection by the users, it is often sufficient to establish that no changes have taken place in the lighting or arrangements of the room. The monitor should not be exposed to direct light from other light sources, such as lamps or windows. In addition, these light sources should not be in the visual field of the image viewer.

Quality control of imaging receptors

It is important to monitor the proper condition of image receptors and image viewing devices and equipment in order to ensure sufficient image quality. The best instructions for performing adequate quality control can be obtained from the equipment manufacturer. For example, for flat panel detectors, equipment manufacturers recommend periodic uniformity calibration to ensure the uniformity of the image.