8 August 1989 Applications Of The One-Dimensional Diffusion Approximation To Biological Tissue
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Abstract
Radiative transfer relates the macroscopic optical properties of a light scattering and absorbing material to microscopic parameters characterizing the individual particles, usually the absorption coefficient (k), total scattering coefficient (s), and mean cosine of the scattering angle (g). In densely scattering media the numerical values of these parameters must be calculated by fitting experimental quantities to theory, typically the transmission coefficient (T), reflection coefficient (R), and a third parameter such as the attenuation depth (3). Approximate radiative transfer theories have been employed to solve thT "inverse problem" for practical geometries. The recent review of Star t al. describes some mathematical models of current interest. The diffu ion approximation treats light propagation in a turbid medium as equiva-lent to particle diffusion. Comparisons of flux density distributions calculated with the diffusion approximation and Monte Carlo simulations suggest1 that the diffusion approximation is most accurate for k << s(1 - g) and low g. The parameter s' = s(1 g) is the reduced scattering coefficient. HoweyeE,3 recent measurements on animal tissues led to values of g close to unity. ' The purpose of the present work was to construct a diffuse optics spectro-photometer for measuring the optical properties of tissue layers over a wide spectral range and analyze the experimental results with two formulations of the one-dimensional diffusion approximation based on different angular scattering distributions or "phase functions".
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Leonard I. Grossweiner, Zengyao Zhang, Bess Grossweiner, James L. Karagiannes, "Applications Of The One-Dimensional Diffusion Approximation To Biological Tissue", Proc. SPIE 1064, Thermal and Optical Interactions with Biological and Related Composite Materials, (8 August 1989); doi: 10.1117/12.951950; https://doi.org/10.1117/12.951950
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