Abstract: Non-specific thermal injury to the epidermis may occur as a result of laser treatment of cutaneous hypervascular malformations (e.g. port wine stains) and other dermatoses. Methods to protect the epidermis from thermal injury include sapphire contact cooling (SCC) and cryogen spray cooling (CSC). Evaluation of the skin thermal response to either cooling method and better understanding of the heat transfer process at the skin surface are essential for further optimization of cooling technique during laser therapy. We present internal temperature measurements in an epoxy resin phantom in response to both SCC and CSC, and use the results in conjunction with a mathematical model to predict the temperature distributions within human skin. Based on our results, a conductive heat transfer process at the skin interface appears to be the primary mechanism for both SCC and CSC. In the case of CSC, 'film cooling' rather than 'evaporative cooling' seems to be the dominant mode during the spurt duration. Currently, due to the lower temperature of the cryogen film and its shorter time of application, CSC produces larger temperature reductions at the skin surface and smaller temperature reductions at depths greater than 200 micrometer (i.e., higher spatial selectivity) when compared to SCC. However, SCC can potentially induce temperature reductions comparable to those produced by CSC if a sapphire temperature similar to that for a cryogen could be achieved in practice. !25
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