Computational investigation on thermal responses of blood vessels during laser treatment of port wine stain

Purpose - The purpose of this paper is to present a numerical analysis of the laser surgery of port wine stain (PWS) with cryogen spray cooling to compare the treatment effect between pulse dye laser and Nd:YAG laser, explain the incomplete clear of the lesion and optimize the laser parameter. Design/methodology/approach - The complex structure of skin and PWS is simplified to a multi-layer skin model that consists of top epidermal layer and underneath dermis layer embedded with discrete blood vessels. The cooling effect of cryogen spray before laser firing is quantified by a general correlation obtained recently from the experimental data. The light distribution is modeled by the Monte Carlo method. The heat transfer in skin tissue is calculated by Pennes bioheat transfer model. The thermal damage of blood vessel is quantified by the Arrhenius damage integral. Findings - For the vessel size studied (10-120 ìm), pulse duration is recommended shorter than 6 ms. Large and deeply buried vessels, which may survive from 595 nm laser irradiation, can be coagulated by 1,064 nm laser due to its deep light penetration depth in skin. Furthermore, a desired uniform heating within the large vessel lumen can be achieved by 1,064 nm laser whereas 595 nm laser produce non-uniform heating. Originality/value - The possible reason for the poor responding and incomplete clearance lesions is clarified. Laser wavelength and pulse duration are suggested to improve the clinical results.