Pulsed laser-induced thermal damage and the treatment of port wine stains.

摘要

Cutaneous vascular lesions such as Port Wine Stains (PWS) can have a deleterious effect on an individual both physically and psychologically. Standard treatment of PWS involves pulsed laser irradiation, yet results remain highly variable. Previous studies have indicated that this is due to patient-to-patient variations in vascular morphology and a lack of understanding of laser-tissue interaction mechanisms.; A novel three-dimensional optical-thermal numerical model which has the ability to incorporate arbitrary specification of realistic tissue morphology was described, verified and implemented. The Monte Carlo-based optical model was shown to be in good agreement with previous models incorporating simple geometrical structures, yet provided unique perspectives on light propagation effects. The optical model was then linked with a finite difference thermal model to predict transient changes in temperature and thermal damage. Using tissue morphology specified directly from a tomographically-reconstructed human PWS biopsy, the effect of tissue structure and laser pulse duration were examined. Simulations were performed to analyze the efficacy of cryogen spray cooling for epidermal preservation.; Thermal coagulation of whole blood in vitro by a clinically-used KTP laser was studied. High-speed temperature measurements indicated that coagulation and ablation occurred at higher temperatures than typically assumed in theoretical models. In a study of pulsed holmium laser-induced irradiation of albumen, microsecond-scale changes in coagulum morphology were documented with fast flash photography. Heat conduction effects were indicated to be minimal until several milliseconds after the onset of the laser pulse. Combined experimental and theoretical analyses indicated the basic validity of the Arrhenius equation for quantifying thermal damage during pulsed laser irradiation of both albumen and whole blood.; A parametric computational analysis was performed on the effect of laser wavelength, pulse duration, vessel size, and thermal destruction criteria on laser treatment of PWS. Although standard PWS treatment parameters were predicted to bring about selective damage with minimal collateral damage in most cases, variations in parameters may help to minimize thermal and ablative damage in certain cases.; These investigations have helped to improve the realism of numerical modeling of laser-tissue interactions and elucidated optical, thermal, and damage mechanisms related to pulsed laser treatment of PWS and other therapeutic laser applications.