Accessory Apparatus

Positioning Equipment

• Accessory items are frequently as im­portant as the x-ray machine itself. Included are positioning aids, cassette holders, beam-collimation devices, beam filters, and grids.

• Most items are available commercially, but some may be produced locally to better satisfy needs created by a specific machine or situation.

 Aids in Positioning

• Positioning aids are perhaps the most important of the accessory equipment items. These devices are usually wooden blocks placed to ensure that the foot or digit and cassette are held in the same position on successive studies with little risk of motion.

• The type of blocks required depends entirely on the specific X-ray machine and the type of radiographic examination de­sired. If the X-ray tube cannot be lowered to floor level, it is necessary to elevate the foot to allow true lateral projections. Ex­amples of positioning aids are presented in the discussion on specific radiographic positioning.

Top Cassette Holder

• Cassette holders are essential as radia­tion protection devices. Although an operator wears protective lead gloves and a lead apron, it is an unacceptable practice to position the hands or any part of the body within the primary x-ray beam.

• A slot may be cut in a wooden positioning device and serve to hold the cassette. The cassette holder may be fashioned of metal or wood with a handle that permits the assistant to remain outside the primary beam.

Top Beam-Collimation Devices

• X-rays radiate from the target in the tube in straight lines in all directions. The rays that escape from the tube form the primary beam.

• It is important that x-ray machines be equipped with a method of controlling the size of the primary beam as it leaves the tube.

• Control of the beam size means that a smaller area on the pa­tient is exposed to radiation, and expo­sure to the primary beam of persons as­sisting with the examination is more easily avoided.

• By limiting the area of tissue exposed to the primary beam, the amount of secondary or "scatter" radia­tion is also lowered. Scatter radiation is "soft," less penetrating radiation that is produced when the primary beam strikes an object.

• It travels in all directions and, in sufficient amounts, can cause general­ized graying of the film Many different types of cones, cylin­ders, lead apertures, and lead-shutter dia­phragms are available for controlling the size of the primary beam.

• These items range from simple, inexpen­sive lead apertures to costly lead-shutter diaphragms. Frequently, the field of pri­mary radiation is illuminated by a light so that the irradiated area is more easily determined. When used with an adjust­able lead-shutter diaphragm, an illumi­nated field permits exposure of the small­est area compatible with a diagnostic study.

Top Grids

• A grid is a thin wafer with alternating lead and radiolucent strips. Grids are used to decrease the amount of secondary radi­ation reaching the film, which produces "fogging" and a gray film lacking in con­trast. 

Top The table

• The most important requirement of any table used for veterinary radiography is rigidity, although it should not be fixed to the floor. Usually the employment for clinical examinations serves both purposes.

• Cassette stands, troughs, plain wooden blocks, sandbags and soft pads.

Top Lead Aprons and Gloves

• In veterinary medicine, radiography should not be considered unless lead aprons and gloves are available. Even if anesthetization of all animals to be examined radiographically is standard procedure, undoubtedly em­ergency situations will arise or there will be animals requiring radiography that cannot be safely anesthetized.

• In such situations, some one will have to hold the animal during exposure. The individual holding the animal should wear protective gloves having at least a 0.5-mm lead equivalent. Lead aprons should have a minimum of 0.25-mm lead.

Top Collimators

• Collimators are essential for safety. They are used to limit the primary x-ray beam to the size of the x-ray film being used.

• Lack of a cone diaphragm allows the primary x-ray beam to cover a very wide area, need­lessly exposing those holding the animal as well as producing additional scattered radia­tion.

• Most cones have a lead diaphragm within their base to limit the x-ray beam; therefore, the actual cone is mainly used for aiming and centering of the x-ray beam. Diaphragm sizes should vary or be adjustable for each x-ray film size used.

•  Collimators with light-centering devices are available. These devices may direct either a point of light at the center of the field covered by the x-ray beam or a light that outlines the entire field covered by the x-ray beam.

TopGrid

• A grid is made of a sheet of lead strips (perpendicular to the x-ray beam) laid side by side with radiolucent spaces between them.

• Grids have the same size as the x-ray cassette and are placed directly upon or within a cassette between the animal being examined and the film. A grid's purpose is to allow only the primary x-ray beam to pass through to expose the x-ray film.

• The secondary or scattered radiation is stopped because it is at an angle to the lead strips and is absorbed. A grid is a must for good radiography of thick part more than 11cm thick to reduce the fog caused by scatter radiation to import the details.

  Top Film Markers

• All radiographs are legal records. Each radiograph made must be permanently iden­tified at the time of exposure in the follow­ing manner:

• Veterinarian's name or hospital.

• Case number (identification).

• Date radiograph was taken.

• This information should be placed on the X-ray film prior to development and not written upon the film later.

• The most convenient method of making the notation is by use of a permanent nameplate containing the name of the veterinarian or hospital in lead letters or letters punched out of a lead plate and used as a stencil. Case numbers and dates in lead letters or numbers can be attached to the nameplate. Top