Abstract: Non-specific thermal injury to the epidermis may occuras a result of laser treatment of cutaneoushypervascular malformations (e.g. port wine stains) andother dermatoses. Methods to protect the epidermis fromthermal injury include sapphire contact cooling (SCC)and cryogen spray cooling (CSC). Evaluation of the skinthermal response to either cooling method and betterunderstanding of the heat transfer process at the skinsurface are essential for further optimization ofcooling technique during laser therapy. We presentinternal temperature measurements in an epoxy resinphantom in response to both SCC and CSC, and use theresults in conjunction with a mathematical model topredict the temperature distributions within humanskin. Based on our results, a conductive heat transferprocess at the skin interface appears to be the primarymechanism for both SCC and CSC. In the case of CSC,'film cooling' rather than 'evaporative cooling' seemsto be the dominant mode during the spurt duration.Currently, due to the lower temperature of the cryogenfilm and its shorter time of application, CSC produceslarger temperature reductions at the skin surface andsmaller temperature reductions at depths greater than200 micrometer (i.e., higher spatial selectivity) whencompared to SCC. However, SCC can potentially inducetemperature reductions comparable to those produced byCSC if a sapphire temperature similar to that for acryogen could be achieved in practice. !25
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