Theoretical investigation on thermal responses of Port Wine Stain lesions to 585 nm , 595 nm and 1064 nm lasers

As a kind of congenital vascular malformations, Port Wine Stain (PWS) is composed of ectatic venular capillary blood vessels buried within healthy dermis. In clinic, Pulsed Dye Laser (PDL) in visible band (e.g. 585 or 595 nm) together with cryogen spray cooling has become the golden standard for treatment of PWS. However, due to the limited energy penetration depth of the PDL, deeply buried blood vessels are likely to survive from the laser irradiation and complete clearance of the lesion is rarely achieved. Nd:YAG laser in near infrared (1064nm) has great potential in the laser treatment of PWS due to its deeper penetration depth in tissue. In this study, the effect of wavelength in treating PWS lesions with various melanin concentrations in epidermis was theoretically investigated by a two-temperature model, in which two energy equations for blood and surrounding dermal tissue are constructed following the local thermal non-equilibrium theory of porous media. The results show that deeply buried blood vessels, which are likely to survive from PDL with wavelengths of 585 and 595 nm, can be coagulated by dual-wavelength laser combing 585 or 595 nm with 1064 nm laser. Furthermore, the dual-wavelength laser of 595 with 1064nm shows better treatment effect than dual-wavelength laser combing 585 and 1064 nm. Key-Words: Port Wine Stain; Pulsed dye laser; Nd:YAG laser; two-temperature model; dual-wavelength laser