Thermal imaging is performed using an infra-red imaging camera that looks at body surface heat which may be radiated or reflected. The fact that the detected infra-red frequencies are a function of object surface temperature makes it possible for the camera to measure and display this temperature. Areas of increased circulation and inflammation show up as "hot spots" on the picture, as do areas where hair is thin, according to different hair colours and also according to external influences such as draughts and radiant heat from sun-heated walls etc. Interpretation of the thermal image must take into consideration what can be seen and sensed without the camera. Thermal imaging is rarely sufficient to give a minutely precise diagnosis on its own without a thorough physical examination too, although some seem to try and some from as far away as the USA!
Using the thermal imaging camera Roger can look at your whole horse and identify any and all areas that show up as hot spots. Problem areas invariably give high readings when checked with the Scenar, thereby quickly and efficiently indicating areas requiring treatment. Hot spots that do not give significant readings with Scenar are frequently artefactual or secondary and may be insignificant. For a fraction of the price it would usually cost to perform a series of nerve blocks, x-rays and ultra-sound investigation and in a fraction of the time Roger can identify your horse's problem areas and can discuss how best to further investigate or treat what has been found.
Surface temperature and radiation is determined by the temperature of the object itself, its surface properties with regard to absorbed or reflected radiation from surrounding objects and atmospheric conditions. The surface temperature as read by the camera is determined by normal thermogenic activities, the underlying blood circulation and any local inflammation. A horse/pony should have been stabled with no rugs or boots etc for at least an hour prior to imaging so that any heat that shows up cannot be caused by anything that was previously worn. Similarly, the stable should not have draughts or radiating sun heat from one side that can cause hot or cold areas.
Inflamed structures are more easily identified the closer they are to the body surface. This makes thermal imaging ideal for identifying areas of inflammation in horse's legs and joints but more difficult for identifying inflammation in deeper structures within the abdomen for example. Given that digestion is primarily by fermentation within the high volume large colon you would expect the abdomen to always read the heat given out by the fermentation process as can be seen in the picture of the whole horse below. Notice how the legs are cooler. On the head and neck shot notice how the eyes and muzzle are much hotter and the mane shields the body heat of the top line of the neck and forehead.
History: This horse had previously had an injury to the carpus ("knee") of the right foreleg that had left a scar but no other signs. For the 2 years after that injury the horse was sound and was show-jumping at a fairly high level without any problems. One day when being collected from the field the carpus was discovered to be again swollen for no known reason and for the next 6 weeks there was a slight intermittent shortness in stride on the right foreleg but was otherwise sound throughout. It was automatically assumed that given the swelling it was an aggravation of the original carpus injury. Readings taken using the scenar indicated that this was not the problem area and treatment there made no improvement to the swelling. It was decided to take a look using thermography ...
The first picture above shows the swollen carpus and the area of scar with no hair is easily discernable as a hotter area - this is due to there being no hair rather than because there is inflammation. Comparison with the other foreleg carpus in the second picture showed there was little to choose between them, however towards the bottom of the picture on the left fore canon area the temperature is significantly cooler than the right fore canon area. This was investigated further
The right fore shows marked increase in temperature below the carpus compared to the left indicating general increased circulation. There is a hotter area to the inside and slightly above the right fetlock suggestive of an area of more specific inflammation. Readings were taken over this area with scenar which were definitely higher than the carpus and indicated an areas requiring treatment with scenar which was performed. The same area was checked after treatment (picture on left below).
Notice how the fetlock is cooler following treatment with the scenar although there are still some areas of heat and the circulation is still increased relative to the left fore. The following day the carpus swelling was reported to be very much reduced which suggested that it had swelled up due to increased blood pressure resulting from increased circulation to the area of inflammation near the fetlock lower down the leg. There had been no swelling in the fetlock area to indicate that the problem lay here. In the second picture (on the right above) above taken 3 days later both front legs have an equal temperature and there is no sign of the inflammation just above the right fetlock. This horse had been exercised on the horse-walker earlier in the day with no sign of shortness in stride or lameness.
No sedation or nerve blocks were required to achieve this result and no animals were harmed during filming!