SELECTIVE COOLING OF BIOLOGICAL TISSUES - APPLICATION FOR THERMALLY MEDIATED THERAPEUTIC PROCEDURES

The ability to control the degree and spatial distribution of cooling in biological tissues during a thermally mediated therapeutic procedur e would be useful for several biomedical applications of lasers. We pr esent a theory based on the solution of the heat conduction equation t hat demonstrates the feasibility of selectively cooling biological tis sues. Model predictions are compared with infrared thermal measurement s of in vivo human skin in response to cooling by a cryogen spurt. The presence of a boundary layer, undergoing a liquid-vapour phase transi tion, is associated with a relatively large thermal convection coeffic ient (approximate to 40 kW m(-2) K-1), which gives rise to the observe d surface temperature reductions (30-40 degrees C). The degree and the spatial-temporal distribution of cooling are shown to be directly rel ated to the cryogen spurt duration.