Medical Infrared Imaging

This chapter describes passive as well as active thermal methods and their applications in medicine. To keep the body temperature at a constant level, excess heat is released by evaporation, convection, conduction, and radiation. Evaporation of sweat is the most obvious mechanism. Its effectiveness depends upon the ambient temperature and relative humidity. Convective cooling is most noticeable when standing in front of a fan. Conduction occurs when physically touching an object. Conductive cooling depends on the temperature difference between the object temperature and the skin temperature. Feverish patients are sometimes immersed in cool water. Radiative cooling is a function of the skin temperature and the environmental temperature. It is experienced when placing your hand in a freezer. An infrared (thermal) imaging system is calibrated to provide surface temperature. Local variations in skin temperature is a function the above quantities as well as metabolism (cancers and exercise), inflammation, circulatory disturbances, and skin condition (scabs, moles, and hair).