Sr. Health Physicist
Radiation and radioactive materials aren’t just used for human medical purposes. Animals that are sick or hurt benefit as well, in methods similar to those used by medical doctors.
By far, the most common use of radiation in a veterinary practice is from x-ray machines. An x-ray machine uses electricity to produce low-energy radiation that passes through soft substances such as skin and muscle, but not through hard substances like bone or metal. So when a veterinarian suspects your dog has a broken leg, he uses an x-ray machine to obtain a picture, called a radiograph.
Radiographs can also spot objects that animals have swallowed by mistake, such as lead sinkers lost in a pond or stream by a fisherman.
While x-ray machines are regulated by state agencies, not the NRC, other activities performed by veterinarians do require an NRC license. One common radioactive material, technetium-99m or tech-99m as it’s often called, is used to diagnose bone damage too small to be seen by x-rays. This type of diagnosis, called a “bone scan,” is performed often in horses used for racing or jumping.
The horse is injected with a tech-99m-labelled compound that acts like calcium and concentrates in the bones. The compound emits low-energy gamma rays that can be detected by a “gamma camera.” Because most of the gamma radiation will come from the bony areas of the horse, a picture of the bone can be seen. Damaged areas will have high concentrations of the tech-99m, allowing the veterinarian to see what areas are causing pain. The radioactive material decays away in a few days. The horse can then go home and be treated for the problems identified in the bone scan.
Vets commonly use another isotope, iodine-131, to treat feline hyperthyroidism. This disease is caused by an overactive thyroid, and cats with this disease become very thin and sick. One possible treatment involves surgery to remove part of the thyroid, so that the cat’s thyroid activities are reduced to normal levels.
Or a veterinarian can use radioactive iodine-131, known as I-131, to reduce thyroid activity. In this type of treatment, a cat is injected with I-131, which will concentrate in the cat’s thyroid and emit gamma radiation that will damage some of the thyroid tissue and reduce thyroid activities to a more normal level. I-131 has an eight-day half-life, so cats treated with it must remain at the vet hospital for several days. Then owners must follow special handling precautions when they return home.
While technetium-99m and iodine-131 are the most commonly used radioisotopes for treating animals, some large veterinary hospitals may also use lasers, computed tomography scans, positron-emission tomography scans, and magnetic resonance imaging. And animals of all sizes, from hamsters to horses, from owls to elephants, may need x-rays – thus benefitting from the careful medical use of radiation.