Multi-layer diffusion approximation for photon transport in biological tissue
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A method for improving the accuracy of the optical diffusion theory for a multi-layer scattering medium is presented. An infinitesimally narrow incident light beam is replaced by multiple isotropic point sources of different strengths that are placed in the scattering medium along the incident beam. The multiple sources are then used to develop a multi-layer diffusion theory. Diffuse reflectance is then computed using the multi-layer diffusion theory and compared with accurate data computed by the Monte Carlo method. This multi-source method is found to be significantly more accurate than the previous single-source method. The appendix to this thesis also shows the derivation of the extrapolated boundary condition. This boundary condition is utilized to solve for the discontinuity that occurs at the tissue-ambient medium interface. The boundary conditions for common index of refraction mismatches are solved for and listed in a table.