Effective source term in the diffusion equation for photon transport in turbid media

摘要

The Green's function for the diffusion equation is widely used to describe photon transport in turbid media. We have performed a series of spectroscopy experiments on a number of uniform turbid media with different optical properties (absorption coefficient in the range 0.03-0.14 cm(-1), reduced scattering coefficient in the range 5-22 cm(-1)). Our experiments have been conducted in the frequency domain, where the measured parameters are the de intensity (I-dc), ac amplitude (1(ac)), and phase (Phi) of the Light intensity wave. In an infinite medium, the Green's function predicts a linear dependence of ln(rI(dc)) and Phi on the source-detector separation r. Our measurements show that the intercepts of these straight lines predicted by the Green's function do not agree with the experimental results. To reproduce the experimental results, we have introduced an effective photon source whose spatial extent and source strength depend on the optical properties of the medium. This effective source term has no effect on the slopes of the straight lines predicted by the Green's function at large values of r. (C) 1997 Optical Society of America