We introduce a micro-optical model of soft biological tissue thatpermits numerical computation of the absolute magnitudes of itsscattering coefficients. A key assumption of the model is that therefractive-index variations caused by microscopic tissue elements canbe treated as particles with sizes distributed according to a skewedlog-normal distribution function. In the limit of an infinitelylarge variance in the particle size, this function has the samepower-law dependence as the volume fractions of the subunits of anideal fractal object. To compute a complete set of opticalcoefficients of a prototypical soft tissue (single-scatteringcoefficient, transport scattering coefficient, backscatteringcoefficient, phase function, and asymmetry parameter), we apply Mietheory to a volume of spheres with sizes distributed according to thetheoretical distribution. A packing factor is included in thecalculation of the optical cross sections to account for correlatedscattering among tightly packed particles. The results suggest thatthe skewed log-normal distribution function, with a shape specified bya limiting fractal dimension of 3.7, is a valid approximation of thesize distribution of scatterers in tissue. In the wavelength range 600 ≤ λ ≤ 1400 nm, the diameters of the scatterers thatcontribute most to backscattering were found to be significantlysmaller (λ/4–λ/2) than the diameters of the scatterersthat cause the greatest extinction of forward-scattered light(3–4λ).
© 1998 Optical Society of America
Joseph M. Schmitt and Gitesh Kumar, "Optical Scattering Properties of Soft Tissue: A Discrete Particle Model," Appl. Opt. 37, 2788-2797 (1998)