Abstract

The study of light propagation in tissue is complicated by the anisotropic, inhomogeneous, and variable character of tissue. We, therefore, used a reproducible tissue phantom to study the influence of beam diameter, absorption μ_a, and scattering μ_s coefficients and refractive index on the propagation of light in an optical phantom at 633 nm. We used mixtures of Intralipid 10% (scattering medium) and Evans Blue (absorbing medium); the optical parameters of these substances were determined by transmission measurements and by the added absorber method using the solution for a point source in an infinite medium in the diffusion approximation. These parameters are: μ_s = 38.6 ± 0.4 mm⁻¹ mliter⁻¹ liter and asymmetry parameter g= 0.71 ± 0.03 for Intralipid 10% and μ_a = (7.60 ± 0.05) × 10⁻³ mm⁻¹ mliter⁻¹ liter for Evans Blue (515 mg/liter). Measurements of the energy fluence rate using an isotropic probe were performed in media with scattering coefficient of 1 mm⁻¹, anisotropy factor of 0.71, absorption coefficient of 1.3 × 10⁻³, 0.01 and 0.05 mm⁻¹, and refractive index of 1.33. The experimental results were compared to an analytical solution of the diffusion approximation to the radiative transport equation. The influence of the beam diameter and the absorption coefficient of the medium on the light penetration appear to be large, and the experimental results show reasonable to good agreement with the theory.

© 1988 Optical Society of America