Thermobiological diagnostics dates back to the time of the ancient Greeks when Hippocrates noted in 480 BC that when a person was covered with mud, the parts that dried first were thought to indicate a pathological condition in that area (Amalu, 2001). In the 1950s, military research into night vision equipment for monitoring troop movements renewed interest in diagnostic thermography, and in 1957, R. Lawson discovered that the skin temperature over an area of breast cancer was higher than that of a normal breast. In 1972, the Department of Health, Education and Welfare issued a position paper saying that medical experts believed thermography had gone beyond the stage of research in four areas: pathology of the female breast..., and in 1982, the Food and Drug Administration approved thermography and classified it as an adjunctive diagnostic screening procedure for breast cancer detection. Since then, thermography has been used for a variety of diagnostic procedures. Some insurance companies are now paying for thermography scans for women to detect breast cancer in its early stages (Fratt, 2003).
In terms of the physics of thermography, all objects with a temperature above absolute zero emit infrared radiation from their surface (Amalu, 2001). The Stefan Boltzmann Law states that "the total radiation emitted by an object is directly proportional to the area of the object emissivity and the fourth power of its absolute temperature." The emissivity of human skin is very high, being within one percent of that of a black body, so measurements of infrared radiation emitted by the skin can be converted directly into accurate temperature values.
Infrared radiation falls within the range of 0.75 microns to 1 mm on the electromagnetic spectrum, and human skin emits infrared radiation in the range of 2-20 microns, peaking on average at 9-10 microns (Amalu, 2001). Infrared detection systems used in diagnosis utilize ultra-sensiti...