Considering thermography to evaluate a horse's legs? Better move that patient inside and shut the doors. Austrian researchers recently learned that wind and air drafts can affect themographic readings of horses’ front legs—very quickly, in fact—potentially leading to false positive or negative results.
“I was surprised at how fast the temperature decreased after the onset of airflow,” said Simone Westermann, DrMedVet, a researcher in the Units of Large Animal Surgery and Orthopaedics at the University of Veterinary Medicine in Vienna. Westermann and her fellow University of Veterinary Medicine researchers studied the effects of air, angles, distances, and natural temperature differences on multiple thermographic readings of 16 healthy adult horses.
Slight drafts of air—what Westermann called “barely noticeable wind velocities”—caused a reduction in the temperature of horses’ forelimbs, compared to the temperature recorded without drafts, she said. A gentle breeze of only two meters per second could make leg temperatures drop as much as 1.5°C (2.7°F) in as few as one to three minutes.
Temperature can also naturally vary slightly from one forelimb to the other in a healthy horse, according to Westermann’s research, so those evaluating thermographic readings should take into consideration the possibility of natural differences between legs.
Angles and distances of the position of the thermography reader compared to the limb can also cause some variations in reading, but fortunately these parameters do not have to be precisely consistent every time, Westermann said. Slight changes in angle (up to 20°) and distance (up to 50 centimeters, or 19 inches) caused no significant differences in thermographic results from one reading to the next.
“We can tolerate certain variations in camera angle and distance,” Westermann said. “But airflow can be a problem that you should keep in mind. It’s necessary to perform thermography in a place without airflow to avoid false negative or positive results.”
The average barn can probably qualify as a draft-free room, she said—“but certainly it depends on the kind of barn.” She said she would not recommend performing thermography outdoors. Even so, this extra effort should not dissuade practitioners from benefiting from this unique diagnostic tool.
“Many veterinarians argue that thermography is too complicated to perform,” she said. “But it’s not more complicated than many other kinds of diagnostic techniques such as (radiography), scintigraphy, and ultrasound. Certainly, it must be used in combination with a clinical examination, and it can only give a hint to the reason for lameness. But with thermography, it’s possible to make physiology visible.”
Additional research in the field is needed, Westermann added.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.