INVESTIGATION OF 2-LAYERED TURBID MEDIA WITH TIME-RESOLVED REFLECTANCE

Light propagation in two-layered turbid media that have an infinitely thick second layer is investigated with time-resolved reflectance. We used a solution of the diffusion equation for this geometry to show th at it is possible to derive the absorption and the reduced scattering coefficients of both layers if the relative reflectance is measured in the time domain at two distances and if the thickness of the first la yer is known. Solutions of the diffusion equation for semi-infinite an d homogeneous turbid media are also applied to fit the reflectance fro m the two-layered turbid media in the time and the frequency domains. It is found that the absorption coefficient of the second layer can be more precisely derived for matched than for mismatched boundary condi tions. In the frequency domain, its determination is further improved if phase and modulation data are used instead of phase and steady-stat e reflectance data. Measurements of the time-resolved reflectance were performed on solid two-layered tissue phantoms that confirmed the the oretical results. (C) 1998 Optical Society of America.