Thermography: Hot Images and a Hot Topic

When preparing the equine athlete, the typical trainer anticipates long-term soundness, yet agonizes about injury. Horsemen know that as the horse performs to a higher standard, he will probably experience varying amounts of soreness and pain. Just as no one can predict how the equine athlete will perform, so no person can forecast the effects of stress on each horse's body. Increased pressure on the athlete's musculoskeletal system can improve performance, as the horse adjusts his gaits to greater demands of distance, height, or speed.

The technology of diagnostic imaging can help the veterinarian to assess the athlete's soundness. For horses, techniques include ultrasound (sonography), radiography, and thermography.

Thermography measures body surface temperature and depicts inflammation by detecting and displaying heat.

Because animals can't verbally communicate the location and extent of pain, detecting a source of discomfort challenges the equine practitioner. Thermography can help identify the source of pain. A researcher in this technology, Ram Purohit PhD, noted, "Thermography may act as a 'pain substitute' because of its ability to detect inflammation in the early stages before tissue damage occurs."

Steven Kamerling, PhD, Professor of Pharmacology at Louisiana State University's School of Veterinary Medicine and a registered pharmacist, uses thermography in his work in the Veterinary Physiology, Pharmacology, and Toxicology Department.

"Thermography has been of interest for a while," Kamerling said. "It's controversial, with the questions of does it predict the potential for injury or promote healing? There's not a lot of agreement about how effective it is."

Thermography was first used in medicine in the 1950s, the same decade that sonography was applied to this science. Unlike the popular ultrasound, however, thermograms have not won wide acceptance in the medical community.

Defining Thermography

Thermography is a means of examining the horse through a pictorial representation of skin temperature. The technique detects thermal emissions of normal, hotter, and cooler areas, and a thermogram displays slight temperature variations as visual images. The thermogram visualizes the skin temperature distribution pattern in an image that resembles a topographical map of the temperature of the body surface.

"A medical thermogram represents the surface temperatures of skin, making thermography useful for the detection of inflammation," noted Tracy Turner, DVM, Associate Professor at the University of Minnesota College of Veterinary Medicine. "This ability to non-invasively assess inflammatory change makes thermography an ideal imaging tool to aid in the diagnosis of certain lameness conditions in the horse."

Turner views thermography as useful in detecting soft tissue injuries. The skin dissipates heat and is usually cooler than the body itself. Inflamed tissue causes variation in skin temperature and generates heat.

Each individual horse generates a thermal pattern, influenced by its blood circulation. Blood conducts heat to the skin, and the skin's temperature results from the rate of blood flow. Every horseman knows that as the horse exercises, muscles warm up and the animal's skin gets hotter.

Researchers have identified certain consistently warmer areas on the horse--the midline (back, chest, between the rear legs, and the length of the belly) and along the major blood vessels of the legs (the palmar vein on the foreleg and saphenous vein on the hindleg). On the foot, the coronary band is the warmest section, with another warm area between the bulbs of
the heel.

As in any diagnosis of the horse, regular examinations develop a standard of normal temperatures. If circulation increases or decreases, the skin in that zone will feel hotter or cooler. A "hot spot" is usually detected directly over an injury. Decreased heat can occur when the blood supply is reduced, such as when blood is shunted to another area.

Thermal Infrared Imaging

Thermography uses infrared heat sensors to display images. A practitioner can use one of two techniques to produce a thermogram. One involves applying to the skin a sheet of latex embedded with liquid crystals. The sheet displays color changes to show temperature variations. The second, more popular with horses, uses a scanner to pick up infrared radiation.

The scanning camera, or thermovision unit, surveys the body to collect infrared energy. This "heat camera" operates on the principle of an object emitting infrared energy as radiation, or invisible rays. Thermography collects the infrared radiation optically, measures the intensity of the infrared light emission, transforms the energy into electrical impulses, then converts the rays into visible light. An electronic display unit shows this picture--a thermogram. The thermogram can be captured on film, videotape, or as a digital file for computerized analysis.

With the horse, this equipment results in an immediate image. The horse can be held immobile in stocks, and the camera can be held at a safe distance from the animal. The thermogram is taken and displayed instantaneously, without affecting the patient.

This technology is expensive, and its price has fueled the controversy surrounding thermography. One company advertises its state-of-the-art camera at $25,000. This "point and shoot" camera delivers images via a software application that runs under Microsoft Windows.

With a substantial investment in equipment, the resulting thermogram is priced accordingly. Practitioners have been charged with promoting the tool for financial gain, in order to recoup the hardware acquisition.

Assessment Via Thermography

Kamerling uses thermography in his equine research to predict the effect and influence of therapeutic drug treatments.

"It is helpful as a research tool," he said. "I can watch the effect of the drug."

Users enthusiastically praise the procedure's value as an objective assessment of joint inflammation and muscle injuries. Ronald Riegel, DVM, reported from the Scioto Valley Veterinary Clinic, Ostrander, Ohio: "Thermography can be used to monitor the progress of treatment for a joint injury by measuring decreases in radiant heat at the injury site, or to determine the exact condition of a performance horse in a pre-purchase screening exam."

Purohit, the researcher into the technology, noted: "Thermography was efficacious in localizing the area of involvement and aided in establishing the necessary information needed for deciding what further diagnostic methods were to be used." He described using thermography on a horse showing back pain, and the image localized the lesion over the third lumbar vertebrae.

Thermography can diagnose potential conditions through changes in heat, before the horse shows any clinical signs of injury. For example, lameness can be detected as an early inflammation, prior to the horse breaking down in training or competition. It can also reveal hidden signs that other diagnostic tools don't detect.

A horse which was treated for an injury might not be completely healed. A thermogram can show that the inflammation has not completely dissipated from the treated area, and thermal patterns suggest additional therapy.

Horses which exhibit no changes through radiographs have shown increased heat through thermography. Continued stress might compromise their soundness.

For example, a horse might appear sound even though a lesion exists, such as a cal-cium deposit on a bone. The radiograph depicts the lesion; a thermogram of the same area can show an inflammation that tells the practitioner more about the animal's condition.

In the foot, thermograms can provide additional information about such conditions as navicular disease, laminitis, abscesses, and corns. Turner noted that thermography is especially useful in evaluating navicular syndrome as exercise intensifies the hot spot.

"Thermography is one of the few methods of readily determining the relative blood flow to the navicular area," he reported. "For blood flow assessment, the foot is thermographically evaluated before and after exercise. The normal horse will sustain a 0.5 degree Centigrade increase in the temperature of the foot after exercise, but most horses with navicular syndrome will not sustain this increase in the caudal foot due to the low blood flow."

Purohit reported thermographic evaluation of laminitis in his 1980 research. On a mare suspected of imminently developing laminitis, thermograms showed increased heat, although an examination detected no heat in the hoof. Thermograms showed an exaggerated pattern at and below the coronary band--the difference between the hoof and the coronary band is usually three to five degrees Centigrade cooler.

Turner explained: "As the hoof begins to approach the temperature of the coronary band, this indicates an inflammatory problem." He added that thermography can also help detect the development of laminitis in the "good" leg of a horse which suffered an injury in a foreleg. When an injured horse bears excess weight on a sound leg, there is the risk of laminitis, so if the practitioner discovers such inflammation, he can begin therapy before laminitis becomes irreversible.

Thermography also can predict and monitor joint inflammation. Normally cool joints might change their thermal pattern before the onset of lameness. The damaged joint can be detected as the hottest area (except for the front of the hock, which has a vertical hot spot along the saphenous vein). The practitioner can also use thermography to monitor the effect of treatments that replaced synovial fluid.

"Thermography may have its greatest clinical application in the assessment of individual muscle injuries which are difficult to diagnose," noted Turner. "It can locate an area of inflammation associated with a muscle or muscle group, and it illustrates atrophy well before it becomes apparent clinically."

He has identified muscle problems in the shoulder, back, and hindlimb.

Apart from the legs, another use for thermography was reported by Riegel. The American Quarter Horse Association prohibits the practice of "blocking" the horse's tail, and "tail testers" examine horses at AQHA shows. Riegel used thermography on show horses to detect blocked tails. A thermogram also can aid the horse show exhibitor in screening prospects for this forbidden operation.

Turning up the Heat

Thermography has sparked criticism in the medical community. Proponents note that thermography can help diagnose humans' workplace injuries of repetitive strain injury (RSI) and carpal tunnel syndrome, along with the effects of pain blockers on arthritis. However, the American Academy of Orthopaedic Surgeons have labeled the procedure "worthless" and of unverified diagnostic value.

Thermography is an unspecific test, as skin temperature variations aren't specifically related to a definite cause. Its results are not considered as reliable as other diagnostic tools such as ultrasound.

"I believe some of the criticism from the human field is that it does not provide a magical diagnosis," Turner said, "I believe many people, especially chiropractors, thought it would zoom in on a specific problem and provide graphic evidence of the problem and cures. What they found was much more complicated, and I believe there is a learning curve with this instrument. In the 1980s, the U.S. courts accepted thermography as documented evidence of pain; this became very important in workers' compensation suits. Unfortunately, I think some practitioners found that the instrument did not "back up" their clinical impression and they became disenchanted with the technology."

The American Academy of Orthopaedic Surgeons released an advisory statement in 1991 stating that: "A review of the literature indicates a lack of specificity, reliability, and reproducibility for this technique." This organization contended that thermography was not scientifically justified as a clinically useful diagnostic or prognostic test.

Another argument against the procedure could be the likelihood of premature judgment. Anyone can see the colors of hot spots on a thermogram, which makes it easy to arrive at a possibly erroneous conclusion. Yet, interpreting the significance of the temperature variations and acting on that analysis does require a trained practitioner.

The application of thermography outside medicine also clouds its validity. Various firms use the technique for heat inspection of inanimate objects, advertising it for use on buildings and equipment such as electrical, heating, and roofing systems. An independent institute, the Academy of Thermographic Training, promotes the technology through its World Wide Web site.

Thermography In Perspective

Proponents note that the practitioner needs to relate the pattern of thermal change with clinical information. By itself, the resulting image can show a finding of thermal asymmetry. Combined with clinical data, the thermal pattern can contribute to a more likely diagnosis.

With interpretation, thermography can direct management. It displays information on heat and shows the limits of inflammation. The practitioner can then use this data to diagnose and select therapy.

Few practicing veterinarians have this tool in their clinics. The equipment's price and the skepticism of the medical community have limited its widespread application.

Thermography is affected by light and temperature, and conditions affect the performance of the equipment. Kamerling noted the importance of limiting any disruption to the procedure: "I use thermography in a very controlled environment. I keep the horse in one room and the measurements the same."

Outside a laboratory, the practitioner might not have access to the ideal setting of a darkened chamber in the range of 20 degrees Centigrade (68 degrees Fahrenheit).

"The thermographic area ideally should have a steady, uniform airflow so that erroneous cooling does not occur," Turner explained. "Practically, the horse should be kept from drafts. Likewise, the horse should be allowed 10-20 minutes to acclimate to the environment or room where the thermography is performed."

Advocates of the procedure recommend that the operator must assure the quality of the image. Although current models allow simple use, the test can be distorted. The temperature of the surrounding environment affects the heat of the skin. Even the length of a horse's hair coat can distort the image, as longer hair insulates the leg. (Fetlock and pastern hair should be clipped.) To determine the presence of a hot spot, the operator should make at least two images from two angles.

Thermography seems most instrumental as an investigative procedure that provides clues for further examination. The technology excels at locating areas of injury, which the practitioner can examine with other diagnostic imaging tools.

"Ultrasound and thermography provide different information," Turner said. "Thermography provides a location, and radiology and ultrasound will better characterize the problem, once you know where it is."

As an example, he explained that thermal changes of a healing tendon can mislead assessment, as the thermal pattern diffuses. Examination through ultrasound can show a different picture of the abnormality.

In veterinary medicine, thermography offers the benefit of finding potential problems. Even though the ailing horse can't vocalize his injury, he can "talk" to the veterinarian through his body heat.

About the Author

Charlene Strickland

Award-winning writer Charlene Strickland lives in Bosque Farms, N.M. She has published 8 books and over 600 magazine articles, and is a member of the International Alliance of Equestrian Journalists.

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