Random walk methodology for determining optical properties of tissue from reflection and transmission measurements

A new iterative inverse method to calculate absorption and scattering coefficients of optically turbid media from total reflectance and transmittance measured by integrating spheres is proposed and evaluated. Random walk methodology is used to calculate the total reflectance and transmittance of light from highly turbid slabs whose refractive index differs from that of the surrounding medium. Photon migration near index-mismatched boundaries is inferred from Monte-Carlo simulations that take into account significant angularly-dependent internal reflection. An inverse method is used to determine the optical coefficients, μ_a and μ_s, from diffuse reflectance and transmittance measurements on suspensions of polystyrene latex beads, the optical absorbance being varied by adding dyes to the suspension medium. The nominal optical coefficients (μ_a from 0.01-0.09 mm^-1 and μ_s from 1-2 mm^-1) are found to agree on average within 8% of the values calculated by the inverse method. The use of the method for tissue characterizations is illustrated by determining the optical parameters of samples of bovine myocardium and human breast.