Effective care and maintenance of x-ray machines improves the overall safety and risk of harmful exposure levels. Following are many of the questions we receive from radiation workers in veterinary practices.
Why measure temperature in processors?
Developer temperature is a major determinant of X-ray image quality. It must be kept at the manufacturer’s recommended level. This is best accomplished with the use of a thermometer. Film is designed to be processed in a time and temperature fashion. Often the label on the film box will state that the optimum developing times occur within a specific temperature range. Automatic film processors are designed to treat film for fixed periods of time that frequently do not change. Hence, the temperature must be controlled to accommodate the fixed times that the film is in the processor. The problem is that the temperature controlling device in the processor does not always work properly. Some processors display the developer temperature. Others use lights or some other indicator to show that the temperature is in the correct range and still others have no indicators at all. One of the most common failures associated with automatic film processors is incorrect developer temperature. In the case of wet line development (also known as tank development) the temperature of the water bath around the developer and fixer tanks is often controlled by a thermostatic valve. This valve can malfunction over time and change the water temperature of the bath. Therefore it is necessary to track the temperature of the developer with a suitable thermometer.
What is a suitable thermometer?
Any good quality digital or analog thermometer can be used to measure developer temp. Do not use a mercury in glass thermometer. Pet shops sell simple thermometers which can display either colors or numbers that indicate the temperature. These can be immersed in the developer solution or attached to the walls of the tank. Electronic shops sell simple indoor/outdoor thermometers that have a remote probe for measuring outdoor temperature. The probe is often very small and is covered with PVC, Teflon or some other material that is immune to developer chemicals. This probe can be immersed in the developer tank and the temperature display attached to a wall near the processor for easy reading. Use your imagination. Just monitor and record the developer temperature in a way that is simple, easy to record and reliable. Optimum image quality depends a great deal on the correct developer temperature.
What are exposure factors?
There are three exposure factors that can be set up on an x-ray machine that are critical to image quality. These are KV (the penetrating energy of the x-ray beam), Ma (also known as tube current and which determines the quantity of x-rays in the beam per unit of time) and Exposure Time (which determines the amount of time that the beam is exposing the patient). In veterinary radiography it is not uncommon to find look up tables that relate the thickness of the patient part to a set of exposure factors. These should be posted in the x-ray room and should be checked to ensure that they match the film screen combinations found in the cassettes. Further, it is a practice requirement in British Columbia to record the exposure factors used in every exam as well as the date of the exposure and other patient information such as thickness, name of animal, type, effectiveness of the factors etc. Radiation surveyors find this information to be invaluable when it comes to determining how well the system is functioning over time. In addition, it also helps to determine the amount and kind of radiation shielding materials that are required to ensure proper shielding of the x-rays generated by the practice. Furthermore, this record provides a valuable guide, if used properly, to determine optimum exposure factors when radiographing a new patient.
What are Technique Charts?
Technique charts are a recorded look-up table that outlines exposure factors for each type of examination. The inspection program accepts pre-selected programs on the machines to substitute for written Technique Charts but does test these for accuracy. One of the ways that technique charts can provide very useful information is to determine over time their effectiveness. If the charts tend to provide improper information over time, it is a good indication that the x-ray machine may need servicing. It is not uncommon to find technique charts modified over time instead of having the machines serviced which is the incorrect way of dealing with “drift” in the performance of the x-ray machine. The exposure characteristics of x-ray machines do change quite dramatically over time and they should be serviced when changes in exposure factors are indicated. If this is not done, it is quite common to have a machine failure during a radiation survey.
Where do I wear my dosimeter badge?
In British Columbia, you wear it under your lead protection device such that it is between the lead and the area of your body of interest. In general, you should wear it somewhere near the center of your body mass. On your belt or on a shirt pocket are two common locations that work. Some individuals desire to determine the radiation exposure in the area of the thyroid in addition to the whole body. If that is the case, the best location for the second badge is on the collar of a shirt or uniform, again under the lead. There are those who wear their badges outside the lead because they want some indication of the radiation that emanates from the system and the patient. The problem with this is that it skews the statistics which result from the combined analysis of worker radiation exposure which is reviewed on a regular basis. Those who analyze the data do not know where the badge was worn. If worn outside the apron, it will record a higher value than if worn under the apron, and the value of the obtained dose is determined to be actual body exposure, which will be incorrect and falsely high.
How to prepare for an X-ray inspection of facility?
The inspection covers a number of steps dealing with the actual performance of the X-ray machines, processing of images, radiation safety, personal protection equipment and Quality Assurance Programs. The best way to prepare for the inspection is to insure that technique charts are posted for each machine, lead aprons, gloves, thyroid shields etc. are in good repair and that a QA program is in place. In addition, exposure records and staff radiation records must be current and visible, the rest of the inspection is technical and there is little that can be done ahead of the inspection. It is a good idea to have on hand a person familiar with the operation of the various systems while the surveyor is on site. Some practices take the step of having their equipment serviced prior to a survey. This is often not necessary as the surveyor may be able to remedy minor problems and most surveyors only check the machines as they are used. Hence, a partially functioning machine can pass a survey if it performs within the limits of Safety Code 28 as it is used.
Should I check Cassettes and Screens against the film that I use?
Yes. It is an observed fact that veterinary practices often use screens and cassettes that are cast off from hospitals. Hospitals today are adopting various forms of digital imaging with the result that film cassettes and screens are no longer used and this bonanza has fallen on many veterinary practices. There is some risk associated with accepting these. The screens may not match the film type used in the practice as to color or speed and the cassettes may have light leaks. Further, exposure techniques are highly dependent on film screen combinations and if several such combinations result from the mixing of screens, cassettes, and film from various sources, exposure factors will result in undesirable images. You are advised to check with a reputable supplier of these products before you institute their use in your practice.
Do the screens in cassettes require service?
Yes. They do become dirty over time and accumulate rubbed off film emulsion. In addition, the glue fastening them to the backing of the cassette often becomes loose. The result is poor film screen contact which degrades the image. Obtain a good quality screen cleaner from your supplier and use it at least annually. There are simple ways of determining film screen contact. Check with your service company or contact your surveyor.
Is digital imaging worth exploring?
If your practice does a lot of radiography digital imaging is a good investment. The cost is high and the returns are such that you end up providing better radiographic services at many levels. However, the cost benefit ratio has to be seriously examined in relation to the alternatives provided by the more traditional, and field proven film based images.
Do I need to wear leaded glasses?
This is not a requirement under Safety Code 28 but it is not a bad idea to wear this additional protection. There is a lot that is not known about the long term effects of reasonably low levels of radiation on the human body and the lens of the eye in particular. If you plan on a long career in veterinary practice and are involved with the taking of radiographs, you are exposing your eyes to the unprotected beam that is scattered from the patient.
What does a surveyor look for in personal radiation protection?
Aprons, gloves, thyroid protectors have to be in good repair, the proper thickness and you must have a sufficient number of these on site. This equipment must be checked annually for any rips or tears. This is easily accomplished by X-raying them.
How should I store lead aprons?
Hang it up on hooks or drape it over a towel bar- do not fold as this will damage the inner lead lining.
What Radiation signage is necessary?
Government approved X-ray radiation warning signs must be displayed on all the entrances leading to the X-ray equipment. Also, darkrooms require signage or indicators to indicate when the room is in use.