Predicting dosimetry for laser coagulation of in vivo cutaneous blood vessels

Port wine stain is a congenital vascular disorder which gives the skin a reddish, frequently raised, appearance. Laser irradiation is the only acceptable treatment modality, but multiple treatments are normally required and complications or incomplete lightening are common. These disappointing results may be caused by failure to match the laser parameters (wavelength, pulse duration, spotsize, and radiant exposure) to the structure of the blood vessels being treated (depth, diameter, and distribution).; This dissertation contains a series of experiments designed to address the problem by working towards a customized laser treatment approach. First, a flexible Monte Carlo analysis program was created which can determine the energy deposition in any arbitrary geometry, including the complicated blood vessel structure seen in vivo. Actual histological data from a port wine stain was used as input to this program to give a realistic estimate of the optical events occurring in laser treatment of port wine stain.; Next, a recently developed imaging technique, optical coherence tomography, was employed to investigate laser-blood vessel interaction and to produce three dimensional images of cutaneous hamster and rat blood vessels. To help determine the desired endpoint for laser treatment, a combination of laser irradiation of exposed subdermal vessels and Monte Carlo modeling was used to estimate the blood vessel fluence needed to cause permanent damage. Finally, proof of concept is shown of a systematic approach to blood vessel treatment. The skin of several hamsters was imaged with optical coherent tomography, and the resulting blood vessel maps used as inputs to the flexible Monte Carlo program. The program determined the minimum laser radiant exposure which had a high probability of destroying the imaged blood vessels. Actual irradiation at these radiant exposures showed results in agreement with predictions. Although human port wine stain is more complex than hamster subdermal blood vessels, these experiments show that a customized approach may be used for efficient laser treatment of vascular disorders.