Quantitative characterization of superficial tissues using diffuse optical spectroscopy

Diffuse Optical Spectroscopy (DOS) can be used to noninvasively determine tissue absorption coefficient (mua) and reduced scattering coefficient (mus') which are then used to extract in-vivo functional information of tissues. For DOS techniques, the interrogation depth is proportional to the source-detector separation, and in order to investigate superficial tissues having thickness less than 1mm, source-detector separations less than 3mm are necessary. However, in this regime, diffusion based methods have proven ineffective for quantitatively examining tissue because diffusion approximations are no longer valid.; The goal of this research is to develop a probe that can be used to determine the optical properties of superficial in-vivo tissues using diffuse optical spectroscopy (DOS) in conjunction with a two-layer diffusion model. The new probe employs a highly scattering layer to diffuse photons emitted from a collimated light source before they enter the sample volume of interest. A modified two-layer (MTL) standard diffusion model is able to describe photon transport in this geometry. Both numerical and experimental results demonstrate that the MTL diffusion model can accurately describe photon transport in the MTL geometry even when the source-detector separation is shorter than 3mm.; With the aid of Monte Carlo simulations, I demonstrate that the interrogation depth can be adjusted by changing the source-detector separation and the thickness of the highly scattering top layer. Based on the simulation results and on practical considerations, a MTL probe was designed for clinical use. The clinical MTL probe was applied to several in-vivo studies. In a rat tumor model, the probe demonstrated excellent ability in discerning early angiogenesis development in the dermis induced by the rat tumor. In addition, the recovered in-vivo human skin absorption and reduced scattering spectra are comparable to ex-vivo measurement results described in the literature. These in-vivo measurement results suggest that the MTL probe has great potential to impact many current clinical applications.