Investigation of two-layered turbid media with steady-state, frequency and time domain reflectance

Light propagation in two-layered turbid media having an infinitely thick second layer is investigated in the steady-state, frequency and time domains. A solution of the diffusion approximation to the transport equation is derived employing the extrapolated boundary condition and the Fourier transform technique. We compare the reflectance calculated from this solution to that computed with Monte Carlo simulations and show good agreement. The derived equations are used to calculate mean optical path lengths in a two-layered model representing a fat layer lying above a muscle layer. The results are applied to interpret near infrared spectroscopy measurements on skeletal muscle. It is shown that the fat layer influences strongly the measurements even if the separation of the source and detector is large.