Estimation of anisotropic optical parameters of tissue in a slab geometry.

The scattering and absorption coefficients of many homogeneous biological tissues such as muscle, skin, white matter in the brain, and dentin are often anisotropically oriented with respect to their bounding interface. In consequence the curves of equal intensity of re-emitted light on the surface of the slab will no longer be circular. We here consider the problem of determining the parameters allowing one to estimate the angles defining anisotropy, directional bias of diffusive spreading, and scattering and absorbing coefficients from data obtained from time-gated measurements of light intensity transmitted through a slab of the tissue. Our model can be solved exactly and leads to accurate approximations in which measured values of the surface intensity are shown to be elliptical. The parameters of the ellipses suffice to estimate the anisotropy of the tissue interior. A summary of the parameter estimates with the observables from which they are found is given in a table. Our analysis is based on a diffusion model.