Investigation of two-layered turbid media with time-resolved reflectance

Light propagation in 2-layered turbid media that have an infinitely thick 2nd layer is studied with time-resolved reflectance. The authors used a soln. of the diffusion equation for this geometry to show that it is possible to derive the absorption and the reduced scattering coeffs. of both layers if the relative reflectance is measured in the time domain at 2 distances and if the thickness of the 1st layer is known. Solns. of the diffusion equation for semi-infinite and homogeneous turbid media are also applied to fit the reflectance from the 2-layered turbid media in the time and the frequency domains. The absorption coeff. of the 2nd layer can be more precisely derived for matched than for mismatched boundary conditions. In the frequency domain, its detn. is further improved if phase and modulation data are used instead of phase and steady-state reflectance data. Measurements of the time-resolved reflectance were performed on solid 2-layered tissue phantoms that confirmed the theor. results.