Abstract
The ability to control the degree and spatial distribution of cooling in biological tissues during a thermally mediated therapeutic procedure would be useful for several biomedical applications of lasers. The authors present a theory based on the solution of the heat conduction equation that demonstrates the feasibility of selectively cooling biological tissues. Model predictions are compared with infrared thermal measurements of in vivo human skin in response to cooling by a cryogen spurt. The presence of a boundary layer, undergoing a liquid-vapour phase transition, is associated with a relatively large thermal convection coefficient ( approximately=40 kW m-2 K-1), which gives rise to the observed surface temperature reductions (30-40 degrees C). The degree and the spatial temporal distribution of cooling are shown to be directly related to the cryogen spurt duration.
Highlights
Selective cooling of biological tissues whereby the degree and spatial distribution of cooling can be achieved in a controlled manner would be of benefitfor several therapeutic procedures in dermatologywhere the objectiveof treatment is to produce irreversible thermal damage to subsurface tissue constituents without destroying or altering superficial structures
Our theory predicts that temperature reductions to less than 0°C at the skin surface can be obtained by large thermal convection coefficients that are associated with a liquid-vapour
The droplets begin to accumulate on the skin surface, creating a boundary layer consisting of cryogen droplets and ice
Summary
Selective cooling of biological tissues whereby the degree and spatial distribution of cooling can be achieved in a controlled manner would be of benefitfor several therapeutic procedures in dermatologywhere the objectiveof treatment is to produce irreversible thermal damage to subsurface tissue constituents without destroying or altering superficial structures. Examples of such procedures include laser treatment of port wine stains (pws), telangiectasias, and a haemangiomas in which the ideal therapeutic outcome is photothermolysis of subsurface dermal blood vessels without damage to the normal overlying epidermis (Anderson and Parris 1983). The heat transfer process resulting from cryogen cooling and the potential dermatologic application to laser treatment of PWS are discussed
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