Effects of relative humidity on laser light transmittance during cryogen spray cooling of in vitro skin phantoms

Abstract

While cryogen spray cooling (CSC) can protect skin epidermis from non-specific thermal damage, spray droplets inflight and the cryogen/frost layer that forms on the skin surface may pose a potential problem for laser light attenuation due to absorption and/or scattering. Employing a hand piece expressly designed for concurrent light and cryogen delivery on skin phantoms, we studied the effect of relative humidity on light transmittance during and after spray cooling. Cryogen spurts were aimed at a microscope glass slide and a deformable agar phantom preheated at 32°C. According to our results, relative humidity plays a very important role in the light transmission during CSC. Light absorption and/or scattering by the spray droplets in-flight and cryogen/frost layer formation at the surface induced light attenuation values of up to 45%. The higher the relative humidity is, the lower the light transmission.