Modeling the effect of wavelength on the pulsed dye laser treatment of port wine stains.

To determine the influence of wavelength on the depth of vascular injury in port wine stains following pulsed dye laser treatment, we calculated fluence rates at wavelengths varying from 415 to 590 nm in a two-layer Monte Carlo model representing the epidermis and the dermis. Calculations were made for four different volumetric fractions of blood in the dermis: 0%, 1%, 5%, and 10%. The depth of the selective vascular injury was determined to be the depth at which the rate of temperature rise at some point within the vessel just equals that at the epidermal-dermal junction. This was maximal between 577 and 590 nm with the maximum shifted toward 590 nm for a greater dermal blood content and for larger vessels. The effect of greater epidermal pigmentation was not only to reduce the depth of vascular injury but to shift slightly the wavelength of the maximum vascular injury to a shorter wavelength.