Two numerical solutions for radiative transport in tissue are presented: the Monte Carlo and the adding-doubling methods. Both methods are appropriate for tissues with internal reflection at boundaries and anisotropic scattering patterns. The adding-doubling method yields accurate solutions in one-dimension. The slower Monte Carlo method is the only exact solution available for finite beam irradiance of tissue. Convolution formulas for calculation of fluence rates for circularly symmetric flat and Gaussian irradiances using the Monte Carlo impulse response are presented.
The delta-Eddington method is extended to include many boundary conditions appropriate for tissue optics. The delta-Eddington method is compared with exact methods. Delta-Eddington reflection and transmission are least accurate for thin tissues and mismatched boundary conditions. Fluence calculations obtained with the delta-Eddington approximation are inaccurate (>50% error) for tissues with both mismatched boundaries and high albedos.
A method and theory for the measurement of the phase function of tissue is presented. The method is shown to have a tendency to overestimate the isotropic scattering component in tissues with mismatched boundaries. A graph is presented to correct the overestimate. The backscattered peak in goniophotometer measurements is shown to result from reflection of the forward peak and not from a backward peak in the phase function. Measurements on human dermis indicate that the phase function can be described by a modified Henyey-Greenstein phase function.
A practical method for measuring the optical properties of tissue as a function of wavelength is presented. Evaluation of the technique indicates that the method is accurate to 10% for all optical properties of tissue when sample thicknesses exceed one optical depth. This technique is applied to bloodless human dermis as a function of wavelength and to bloodless human aorta during moderate power (~100mW/mm2) argon laser irradiation as a function of irradiation time.
S. A. Prahl. Light Transport in Tissue. PhD thesis, University of Texas at Austin, 1988.