Monitoring the condition of X-ray equipment ensures safety

In order to get good X-ray images, it is important that the X-ray equipment functions as intended. The condition and functioning of the X-ray equipment must be monitored regularly in order to maintain the safety of operations at the required level.

Device adjustment, imaging values and filtration

If the X-ray equipment is used to take images where the radiation beam is horizontal, the X-ray equipment must have an adjustable light collimator. In special cases, such as when imaging at a horse race track, it is acceptable to replace the light collimator with an incrementally adjustable collimator and a telescopic director to centre the radiation beam or another device that enables targeting the radiation beam on the cassette. In this case, the equipment must indicate the size of the radiation beam at the imaging distances that are used. The edges of the radiation field and guide lights must not deviate from each other at the used imaging distances by more than 1 cm.

The total filtration of the X-ray tube’s primary radiation must, at a minimum, correspond with 1 mm of aluminium, when the maximum imaging voltage is 60 kV. When the imaging voltage exceeds 60 kV, the total filtration must correspond with 2 mm of aluminium. The value of the total filtration of radiation must be marked on the X-ray tube housing.

When the maximum permitted load indicated by the equipment manufacturer is used, the leakage radiation through the X-ray tube’s protective housing must not exceed the value of 1 mSv per one operating hour at a distance of 1 metre from the focus.

The repeatability of radiation doses must be good enough to maintain the same radiographic density when using the same imaging values. Variation in the radiographic density usually indicates a change in the imaging voltage, current or time, assuming that the film development remains constant.

Films, support plates and development impact doses and image quality

The sensitivity of the films and support plates impacts the required amount of radiation and, consequently, the resulting radiation doses. The more sensitive films and support plates are used, the smaller dose is required. Using sensitive films and support plates may involve the disadvantage of slightly inferior image quality than with less sensitive versions.

When imaging thick targets, such as the stomach cavity of a large dog, it is usually advisable to use sensitive support plates to prevent image quality issues due to motion blur from the long imaging time. In such imaging situations, the image quality can be improved by using a grid. When imaging small bones, fine-grain and mammography cassettes may be useful due to their good resolution. However, these cassettes may not be suitable for routine imaging due to the greater imaging values required. The power of the X-ray equipment may also be a limiting factor, especially when imaging thick targets.

A grid is used to reduce scattered radiation. A grid is a disc with narrow lead strips, or lamellae, with an interposed medium that lets through the X-radiation. The medium is usually aluminium, but carbon fibre is also used these days.

Films can be developed manually or using a development machine. The reason for poor image quality usually lies in film development errors. For this reason, it is important to monitor the development using sensitometer film, for example, at regular intervals to detect expired developing liquid or sudden changes during the development. Use of the ideal development time, temperature and liquid mixing ratio stated by the manufacturer of the developer and fixer ensures the best possible result. The laboratory must be light-tight with sufficient space for appropriate working conditions and to ensure that the undeveloped X-ray film is not exposed or fogged during handling.

For more information, read the guide Säteilyturvallisuus eläinröntgentutkimuksissa (Radiation safety in veterinary X-ray examinations).