Techniques for Radiographing the Elephant Foot and Carpus Using a Portable Equine Radiographic Unit
Diagnostic radiographs of the digits of the front and rear feet of Asian and African elephants have been obtained with a portable equine radiographic unit. Detailed films of the phalanges and metacarpal bones were obtained by using a setting of 15 mA and 80 kVP with a Fischer model FP-200 portable X-ray unit (H.G. Fischer, Inc., Franklin Park, IL; maximum output = 90 KVP and 20 Ma) and using Agfa green-sensitive rare earth all-plastic film cassettes (Agfa, 100 Challenger Road, Ridgefield Park, NJ 07660). The film/screen combination is 400 speed. Carpal radiographs have been obtained by securing a 14"x17" rare earth film cassette to the limb of elephants trained and desensitized to allow this using a wide cloth tape. This method has proved superior to other methods of holding the cassette because of the lengthy exposure time, and the shape of the elephants’ limbs. While these films are not as detailed as those of the digits, the edges of the carpal bones can be assessed, and the joint spaces between the carpal bones can be evaluated.
It is critical to use the correct time setting. This varies with the size of the foot and may take some trials to achieve the optimal settings for each elephant. Adult elephants have distal phalangeal bones that are thin, fragile and attached to the toenail. They are best detailed using a 0.25- to 0.4-sec setting at 80 kVP and 15 mA. Diagnostic films of the proximal and middle phalanges may be obtained using the same technique with a 0.4- to 0.7-sec setting. The distal portion of the metacarpals may be radiographed by using a 0.6- to 0.9-sec setting, while the proximal edge of the metacarpals generally requires an exposure time of 0.75–1.25 sec for optimum detail. These settings have been established with the elephant standing with its foot flat on the cassette, and the portable unit handheld at an approximate 45 degree angle, with the tube head 55 cm from the surface of the foot.
Lateral films of the metacarpals and metatarsals require time settings of 3.0–4.0 sec while anterior-posterior and lateral carpal radiographs have been taken using a 4.0-sec exposure. These studies require that the X-ray unit be set at 80 kVP and 15 mA and secured to a stand with the tube head held at a distance of 45 cm from the surface of the carpus. Adequate detail may be achieved if the elephant is motionless throughout the exposure time.
Tracts caused by chronic draining wounds may be visualized and evaluated by instilling a radiopaque dye deep into the tract, plugging the opening with a cotton wad, and immediately radiographing the area.