Mathematical modelling of dynamic cooling and pre-heating, used to increase the depth of selective damage to blood vessels in laser treatment of port wine stains

A theoretical investigation has been conducted to determine how much the irradiance could be increased by dynamically cooling the skin surface. The heat conduction equation was solved numerically in cylindrical coordinates using a skin model composed of four layers. The laser-light absorption was calculated using Monte Carlo simulations. The transient thermal behavior of skin was modelled when cooling with water at a temperature of 0°C and with liquid nitrogen at a temperature of -196°C. With cooling, an increase in the maximum irradiance by a factor 2.3-3.6 was theoretically permitted depending on the irradiation time, wavelength and mode of cooling. The corresponding increase in vessel selective damage depth was predicted to be 0.4-0.5 mm.