Radiography is a commonly used diagnostic tool in veterinary medicine. It can provide a great deal of information about a pet's disease or injury. Radiography is non-invasive and does not harm the animal.
With any radiographic study there are specific techniques which are used by veterinary radiology assistants in order to obtain diagnostic radiographs.
Positioning
Proper positioning is one of the most important parts of veterinary radiographic technique. A radiographic study always consists of at least two views. The two views are always taken so that the radiographic beams cross at right angles. For instance, to radiograph the abdomen of an animal, take one view with the animal laying on his side and a second view with the animal laying either on his back or on his stomach with the pointed at a 90 degree angle to the table.
While only two views are required for some radiographic studies, three or more views are required for others. For example, to examine the chest radiographically, take one view with the animal lying on the right side, a second view lying on the left side and a third view with the animal positioned either on his back or on his chest.
The purpose for taking more than one radiographic view is to provide a study which is more than one-dimensional. By examining two or more radiographic views, it is easier to pinpoint where an object seen on the radiographic films is located in relation to the other body structures visible in the study.
The veterinarian requesting the study will specify which body parts need to be radiographed and which views must be obtained.
Exposure Technique
Exposure techniques are determined by measuring the thickness of the body part to be radiographed. Take the measurement with the use of a caliper at the thickest area to be radiographed.
Each radiography machine is accompanied by a technique chart which is specific to the individual machine. Use the measurement obtained to determine the machine settings necessary for the study.
Machine settings will consist of the length of time of exposure, the milliampere (mA) and the kilovoltage peak (kVp). The mAs is responsible for the density or blackness of the film. The kVp controls the contrast of the resulting radiographic film. There will be controls on the machine which can be adjusted to produce the proper settings.
The technique chart will also indicate whether the radiographic film should be placed directly on the table top or in the bucky tray located under the table top. Consult the technique chart, place the film in the proper location and center the film so that the radiographic beam passes through the center of the film using the light supplied on the tube.
Once the machine is programmed with the proper settings, collimate the radiographic beam by narrowing the beam no larger than the area to be radiographed, using the light on the tube and the corresponding dials which control the size of the lighted area on the table. The field of light simulates the area of the radiographic beam during radiographic exposure.
Position the animal so that the area of interest is in the center of the film and expose the radiograph by using either the hand switch or the foot pedal. Hold the switch in or the pedal down until the machine has finished beeping.
Each radiographic view will have different exposure settings depending on the thickness of the body part.
Developing
Once the radiographic film has been exposed, the procedure for developing the film will depend on what type of radiographic system is being used. Some radiographic systems are digital and the image is copied into the computer software as soon as the image is exposed. Other digital systems require that the film be fed through a reader which transfers the image from the radiographic plate to the computer software which in turn displays the radiograph on the computer screen.
Other radiographic systems will be traditional rather than digital and the film will either need to be developed using an automatic processor or by hand. Using an automatic processor simply involves feeding the film into the processor and then retrieving the developed film.
Manual film processing involves first placing the film in a developing solution, rinsing the film, placing the film in a fixative, rinsing the film and finally drying the film. Each step requires a specific length of time which is dependent on the temperature. A chart should be available in the darkroom for determining the proper amount of time in each solution. Both automatic and manual processing must be completed in a dark room.
Evaluation
Evaluate the film for quality. Digital radiographs can be manipulated through the computer software to improve the quality of the film if necessary. However, if the positioning of the animal was incorrect, the radiograph will need to be retaken.
In traditional, non-digital radiography, if the film quality is poor, the radiograph will need to be repeated. There is no way to manipulate the radiograph once it is produced.
Safety
Wear protective lead gowns, thyroid shields and gloves when working with radiographic equipment. Never place your hands in the radiographic field even if you are wearing gloves. Wear a radiation exposure badge on the inside of the gown or thyroid shield as close to your throat as possible.
Some states require personnel to be outside of the room when a radiographic exposure is made. In these cases, chemical restraint may be necessary in order to obtain most radiographs. Chemical restraint, in situations where the animal is a candidate for such restraint, makes proper positioning of the animal much simpler and perhaps less stressful for the animal as well as decreasing radiation exposure to radiographic personnel.
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