Converting far infrared image information to other physiological data

Skin temperature is determined by blood-flow rate, structure of subcutaneous tissue, and activities of the sympathetic nervous system, which regulate heat dissipation from the body surface. Because of this, we can noninvasively detect distributions of many physiological functions from thermal images of the skin surface obtained by far infrared (FIR) imaging. If we can describe equations by which we calculate values of some functions from skin temperature, we might be able to analyze pathophysiological abnormalities by remote sensing. However, it is clear that we cannot convert a thermal image into other physiological function images unless we eliminate influences of many environmental conditions, structural variations, and other physiological parameters of skin-surface temperature. One solution is to introduce some physical, chemical, or neurohumoral stress to a patient and then take time-sequential thermal images. Dynamic fluctuation of such physiological functions might be revealed by sequential thermal images taken after stress is applied. We analyzed the theoretical backgrounds to determine regional skin temperature and thus developed application software to carry out the process. This article discusses algorithms we developed for detecting static abnormality or transient change of some physiological functions such as skin blood-flow rate, blood volume in cutaneous and subcutaneous vascular beds, and activities of the sympathetic nervous system.