Micro-optical properties of tissue

The aim of this study was to develop quantitative methods for relating the microstructure of a tissue to the magnitude and wavelength dependence of its scattering coefficient. Two methods, cell counting and spatial frequency analysis, were used to estimate the distribution of sizes of structures imaged by light and electron microscopy. We found that scatterers in the epidermal layer of the skin exhibit a log-normal size distribution, whereas the spatial fluctuations in the index of refraction of dense fibrous tissues, such as the dermis, follow a power law. The correlations in the refractive indices of a variety of tissues exhibit characteristics of a random fractal with a Hurst coefficient between 0.3 and 0.5. Calculated from the measured distributions and volume fractions, the magnitudes of the scattering coefficient and anisotropy parameters of the tissue were found to be within the range 10 < mu(s) < 35 mm(-1) and 0.7 < g < 0.97, depending on wavelength and tissue structure. Our results suggest that analysis of histological images of tissues is a viable method for estimating the optical parameters of tissues and their wavelength dependence.