Diagnosing With Color--Equine Infrared Thermography

It's not uncommon these days to walk into a veterinary clinic and find a group of practitioners gathered around a TV monitor. But don't be misled--they're not checking out a heated moment on the afternoon soaps. Instead, they're most likely viewing the heat patterns of a horse's infrared thermography exam, which can helpthem pinpoint problems and diagnose injuries.

Many veterinarians currently use this heat detection device for infrared imaging, which looks like a video camera. It's used to scan the horse to determine variations in heat patterns on his body. The image it takes can be displayed on a monitor, like a TV screen, for analysis.

Thermography, called IRT for short, is especially useful in identifying fluctuations in blood flow, which can indicate problems in soft tissues. The blood flow can vary, depending on whether circulation is normal or affected by injury. IRT can be an early indicator of a problem because blood flow to an injured area may increase before clinical signs of pain and lameness become evident.

Tracy Turner DVM, of Anoka Equine, in Elk River, Minn., has been working with thermal imaging for a number of years at the University of Minnesota and in his private practice.

"Thermal imaging is detection of heat that an object emits. By measuring what the body emits, we can make a picture of the temperature of the body. What we're looking for, in veterinary thermography, is differences. We can take that information and build conclusions," he said.

The temperature of the horse's skin primarily depends on local circulation, blood flow and metabolism of the cells. For the most part, the metabolism of the cells won't be high enough to be a factor--unless there's a cancer--so veterinarians see skin temperature reflecting the blood flow and circulation of underlying tissues.

Turner said there are five cardinal signs of inflammation: heat, redness, pain, swelling and loss of function.

"Going through the course of a lameness examination, the veterinarian looks at loss of function--that the horseman sees as a lameness problem," said Turner. "Then I look for swelling, pain or heat when I palpate the area. Thermal imaging makes me, as a practitioner, 10 times more sensitive to finding the heat."

Show Me The Heat (Or Cold)

Veterinarians use IRT to help them get a better look at the body's reaction to a potential problem. But it's not as simple as just looking for the hot spots and saying that's where the problem lies.

"We're dealing with a living, breathing object, and heat is produced for a lot of different reasons," said Turner. "We have to understand what a normal thermal pattern is--where the normal hot spots are, where the circulation goes. Once we learn what normal is, everything else is abnormal."

There are many reasons veterinarians might see an abnormality in a scan, such as the horse standing in a breeze. "Once we know the things that can cause an abnormal image, then everything else is pathology," he said. "As we start to interpret it and look at the images, what we see are thermal patterns, and changes from normal patterns."

IRT measures superficial temperature rather than how warm or cold the deeper tissues might be. Anything that might obstruct or insulate against heat radiation from the body--fat, long hair, a muddy coat--could interfere with a proper reading.