Estimation of internal skin temperatures in response to cryogen spray cooling: Implications for laser therapy of port wine stains

In many port wine stain (PWS) patients, successful clearing is not achieved even after multiple laser treatments because of inadequate heat generation within the targeted blood vessels. Use of higher radiant exposures has bee n suggested to improve lesion clearing, but risk of epidermal injury due to nonspecific absorption by melanin increases. It has been demonstrated that cryogen spray cooling (CSC) can protect the epidermis from nonspecific the rmal injury during laser treatment of PWS, Inasmuch as epidermal melanin co ncentration and blood vessel depth vary among patients, evaluation of inter nal skin temperatures in response to CSC is essential for further developme nt and optimization of treatment parameters on an individual patient basis, We present internal temperature measurements in an epoxy resin phantom in response to CSC and use the results in conjunction with a mathematical mode l to predict the temperature distribution within human skin for various coo ling parameters, Measurements on the epoxy resin phantom show that cryogen film temperature is well below the cryogen boiling point, but a poor therma l contact exists at the cryogen-phantom interface. Based on phantom measure ments and model predictions, internal skin temperature reduction remains co nfined to the upper 400 mu m for spurt durations as long as 200 ms. At the end of a 100 ms spurt, our results show a 31 degrees C temperature reductio n at the surface, 12 degrees C at a depth of 100 mu m, and 4 degrees C at a depth of 200 mu m in human skin. Analysis of estimated temperature distrib utions in response to CSC and temperature profiles obtained by pulsed photo thermal radiometry indicates that a significant protective effect is achiev ed at the surface of laser irradiated PWS skin. Protection of the epidermal basal layer, however, poses a greater challenge when high radiant exposure s are used.