An infra-red camera measures and images the emitted infra-red radiation from an object. The fact that radiation is a function of object surface temperature makes it possible for the camera to measue and display this temperature.
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. Inflammed structures are therefore more easily identified the closer they are to the body surface. This makes the camera ideal for identifying areas of inflammation in horse's legs and joints but more difficult for identifying inflammation in deeper structures with 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 topline of the neck and forehead.
In order to get the best diagnostic image it is important that the picture measures radiated heat from deeper structures and isn't indicative of where the horse has been heavily rugged prior to examination, or has been standing in the sun! It is therefore best if any horse or pony to be examined has been standing unrugged in a stable for 10-15 minutes so that hot-spots that are seen are genuine signs of increased circulation or inflammation. For a lameness of unkown origin investigation do not work your horse prior to being investigated as it is useful to have a baseline picture prior to lungeing in order to then see which areas get hotter as a result of work which will indicate which structures are getting more inflammed or which muscles are working hardest.
The following case studies are given as an example of how thermal imaging helped identify an area of problem without the expense of multiple nerve blocks, x-rays and ultra-sound investigations and in double quick time.
Case 1
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 suggstive 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.
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 or noticeable heat in this area detectable by feeling. In the second picture 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!
