Thermogram of the back of a man suffering from ankylosing spondylitis, a rheumatic disease involving the spine and sacro-iliac joints that connect sacral spine with the pelvis. The disease may also involve other joints, notably the shoulder and hip. Thermography provides a colour- coded image of heat distribution over the body, which shows characteristic changes in certain diseases. Here, there is a marked increase in temperature over the lumbar spine and sacro-iliac joints, and an abnormal pattern over the shoulders. Colour coding: yellow = hot, blue = cold, colours represent 0.5 degrees C. increments. Reference disc (left) is at 32 degrees C.