Diagnostic imaging considerations for reptiles (Proceedings)


Diagnostic imaging considerations for reptiles (Proceedings)

Apr 01, 2009

Diagnostic imaging is an underutilized resource in herpetological medicine. Survey radiographs and ultrasound can be used to evaluate many different systems simultaneously, and provide insight into possible problems in a case. To be successful with diagnostic imaging, veterinarians need to acquire a basic knowledge of anatomy regarding the species of interest, methods used to restrain reptiles to collect the images, and the most appropriate techniques used to collect and interpret the results.

There are a variety of resources available to the veterinarian that is trying to learn more about reptile diagnostic imaging. Mader's Reptile Medicine and Surgery (Elsevier/Saunders, 2006) provides an excellent review on the subject. Expert opinions can be obtained either via phone consults or via the internet (e.g., Veterinary Information Network). There are also board certified radiologists that offer consultation services. Regardless of the source, veterinarians have many options when attempting to interpret the findings of a diagnostic image

With over 7,000 different species of reptiles, it is impossible to become comfortable with the anatomic peculiarities of all the reptiles. Fortunately, reptile anatomy is highly conserved among the orders. For simplicity, the reptiles can be categorized into one of four groups: chelonians, lizards, snakes, and crocodilians. The tuatara is not mentioned because it is not considered a common captive reptile. Reptile morphology texts are excellent resources for learning the anatomy of these animals. Short descriptions can also be found in Reptile Medicine and Surgery (Mader, Elsevier/Saunders, 2006) and Clinical Anatomy and Physiology of Exotic Species (O'Malley, Elsevier/Saunders, 2005).

The quality of the equipment used to take radiographs is an important consideration. A radiographic machine to be used for reptiles should be capable of a taking a range of images, which might include day geckos (Phelsuma spp.) to varanids (komodo dragons, Varanus komodoensis). A machine capable of such a range should have a short exposure time. 1/60th of a second or shorter is recommended. The machine should also have a high milliamperes capacity (>300). This is important because of the variability in detail that might be expected among different sized animals. The killivolt peak range should also be large, 40-100 killivolt peak, to accommodate the different sized patients a veterinarian may encounter. The ability to alter the killivolt peak by small increments (e.g., 2 killivolt peak) is important because it will enable the veterinarian to review small details between images. A machine in which the tube can be rotated to provide a horizontal beam is preferred. This will enable the veterinarian to take lateral images on animals in sternal recumbency. This is especially important with large chelonians.

For small patient, dental radiograph machines can be used. The author has used this type of equipment to take "whole body" radiographs of small lizards (e.g., juvenile bearded dragons). The detail from these images, although not always refined, does provide more detail than standard films.

Selecting the correct type of cassette or film is as important as using the correct machine. High-detail, rare earth cassettes are preferred. These cassettes should be used in combination with slow speed, single emulsion (gray) films. This combination provides the best detail for small lizards. Double emulsion (black) films can be used for larger reptiles when small detail is not required. Selecting the correct size cassette and film combination is also an important consideration.

When taking radiographs it is important to always collect at least two images. The most common images are a lateral and dorsoventral or ventrodorsal image. These two, two-dimensional images will provide the most insight into interpreting the anatomy of a three-dimensional reptile. Care should be taken when positioning an animal to ensure that the area of interest can be evaluated.

A reptile must be still to collect the "perfect" image. Taking radiographs on un-anesthetized or restrained reptiles can lead to motion and a loss of detail. The author has found that reptiles can be restrained manually for images or anesthetized. Manual restraint does result in increased radiation exposure for the handlers, so it should be kept to a minimum. Placing blinders over the eyes of a lizard can also be done to minimize movement. The author has found this technique to work well with iguanas, bearded dragons, and varanids. An ophthalmic eye lube is placed in the eyes of the animal and the head is wrapped with vet-wrap (3M products, St. Paul, MN). Dimming the lights and minimizing human movement and speaking in the room will also help reduce the stimuli on the reptile.