How valuable is thermography as a diagnostic technique? Peter Green MRCVS looks at some new findings
Infrared and thermal imaging cameras are now so sensitive that thermographic pictures can show tiny variations in the heat generated by the skin over areas of inflammation or disease.
Thermography can be used on the horse’s back and legs and is popular with some para-veterinary practitioners. The equipment is not especially expensive and the technique is completely non-invasive. Objective research has shown the value of the technique, provided it is coupled with full clinical examination and linked with other diagnostic techniques.
Research showed some time ago that the thermographic temperature images of healthy horse legs varied with time and from leg to leg. More research, published in the EVJ, has investigated the effect of draughts upon the thermograms of horse limbs.
Vets in Vienna took thermograms of the lower legs of 6 adult horses in a completely draught-free room. They then repeated the examination with a measured draught flowing over the legs.
The summer air temperature was about 24oC and the relative humidity about 50%. The draught was set at 3 levels, from barely perceptible at little more than 0.5 metres per second to an obvious warm breeze of 4m/s.
The images obtained were strikingly different. Within 3 minutes of the gentlest of draughts flowing past the horses, the temperature of their legs and hooves had dropped noticeably. The stronger the breeze, the greater the effect, which was not consistent from leg to leg — the leg nearer the draught source got colder than the one further away.
These results confirm that although thermography has a place in diagnosis, clinicians must be extremely careful about using the technique without scrupulous attention to exam conditions.
Breeze, humidity, air temperature and exposure to sun can make such a difference to the results that thermography in the field or stable is likely to be unreliable.
This veterinary news feature was first published in Horse & Hound magazine.