Study of optical properties of skin tissues from ultraviolet to short-wave infrared

Abstract

Accurate knowledge of optical properties of skin tissues is fundamental to the study of tissue optics and development of optical instrumentation in clinics. The goal of research described in this dissertation is to develop a system of experimental methods and theoretical models for the inverse determination of optical parameters of mammalian tissues and various tissue phantoms. Based on the integrating sphere and spatial filtering techniques, various experimental systems have been constructed and improved to measure the diffuse reflectance, the diffuse transmittance, and the collimated transmission of turbid samples from the spectral region of ultraviolet to short-wave infrared. Different Monte Carlo based algorithms have been developed to simulate photon transportation under different experimental configurations based on the radiation transfer theory. The corresponding procedures for inverse determination of optical parameters from the experimental data have been established. We have determined the complex refractive index of polystyrene microspheres as a function of wavelength from using a Monte Carlo model in combination with the Mie phase function. The optical parameters of porcine skin dermis tissues have also been determined by assuming the surface of the dermis samples were flat and smooth. The effect of surface roughness on the inverse determination of bulk optical parameters of a turbid sample has been investigated. We found that the condition of the sample surface plays an important role in determining the light distribution in a turbid sample. Numerical simulations have shown that the surface roughness on scales close to the wavelength of light can significantly affect the values of bulk tissue optical parameters inversely determined from in vitro measurements even for a moderate index mismatch. As a result, we have developed a confocal imaging method to measure the surface profile of slab samples of fresh porcine skin dermis and extracted the profile parameters. With this knowledge, the surface roughness corrected optical parameters of porcine dermis tissue have been determined at the wavelengths of 325, 442, 532, 632.8, 850, 1064, 1330, and .