Thermography, in medicine, is the measurement of thermal radiation, or heat, given off by the human body. The amount of heat
that is emitted by the body depends on several factors, including state of health; in addition, some body areas have a larger blood supply than others and therefore emit more heat. The devices that are used to measure these temperature differences produce electronic signals on an oscilloscope, which can then be photographed on special film or projected onto a television monitor. The image produced is called a thermogram.
Inflammatory diseases can be diagnosed with
thermography, because arthritic conditions, bone tumors and bone infections such as osteomyelitis, and muscle and tendon diseases resulting from inflammation produce heat radiation. Blockages of blood vessels also can be detected, because areas of reduced blood flow produce "cold spots" on a thermogram. Disorders such as atherosclerosis, which causes decreased
circulation to the hands and feet, can therefore be detected in this way. (Interestingly, cigarette smoking also lowers heat emission from the fingers. Circulation does not return to normal for about 1 x/M hours after a single cigarette, as revealed on a thermogram.)
Nerve injury produces cold spots as well, and thermography has proved useful in diagnosing some spine injuries that produce pain and disability but appear normal according to other tests. Thermography, however, is no longer considered useful for detecting breast cancer, because benign conditions such as cysts also produce extra heat and because many women with no breast disease at all have also given false positive readings.