The concept and use of X rays have not changed much since their advent in 1895. The way, however, that images are acquired has changed dramatically. Traditional analog X-ray film, much like the film in your old camera, has been replaced with digital sensor panels; these panels are similar to those found in current digital photographic cameras. Digital imaging has allowed radiologists to easily capture and manipulate radiographs, a feature that reduces X ray costs and exposure, while enhancing image quality. The digital radiograph system at the San Diego Zoo consists of a digital receptor panel and accompanying computer that processes the X-ray signal into a viewable image. The resultant image can be further manipulated to enhance image contrast, orientation, and magnification. Images can also be sent to colleagues and consultants for further review. This equipment is expensive, so how do you keep it safe while an elephant stands on it?
A protective cover needed to be constructed to support the weight of an elephant and protect the valuable sensor panel. Several “tunnel” designs were tested prior to using the sensor panel. Because of the nature of X rays, it was important to use materials for the tunnel that would not inhibit the penetration of the X-ray beam. The first prototype consisted of a 0.5-inch-thick piece of acrylic plastic with plastic upright supports. This would prove to be too fragile for an 8,000-pound elephant. The current tunnel consists of a 1.5-inch piece of plastic supported by 1-inch aluminum uprights. A portable equine X-ray machine is used to generate the X rays necessary to produce a diagnostic image. Because of the size of an elephant’s foot, long exposure times are necessary to produce a quality film. The X-ray machine is also on wheels, in case a curious trunk wants to get hold of it!
All the technology in the world would be useless if you couldn’t get the elephant to cooperate. A large part of elephant radiographic imaging involves behavioral training. With the use of operant conditioning strategies, keepers at the San Diego Zoo have been able to train elephants to present and position their limbs for X-ray imaging. The reward for this formidable task has been the ability to obtain routine digital radiographs of the entire herd of elephants at the Zoo. The elephants are rewarded as well! Because of the size of the animals, limitations of the X-ray machine, and lengthy exposure times, it is necessary for the veterinary staff to take several images of each foot, usually a digit or two at a time. This means that the keepers must station, position, and keep the elephant still for imaging. I am amazed at how well the elephants are trained every time I am asked to take radiographs of them.
Once the radiographs have been taken, veterinarians from the Zoos’ Jennings Hospital review and assess the images, looking for any abnormalities. By taking routine foot radiographs, veterinarians are able to evaluate any soft tissue or boney changes that might occur over time. Because of routine exams and radiographs, as well as exhibit design, the elephants at the San Diego Zoo have some of the most pampered feet around!
Steve Culver is a registered veterinary technician at the San Diego Zoo. Read his previous post, X-ray Results for Ibis.