EFFECTIVE SOURCE-TERM IN THE DIFFUSION EQUATION FOR PHOTON TRANSPORT IN TURBID MEDIA

The Green's function for the diffusion equation is widely used to desc ribe photon transport in turbid media. We have performed a series of s pectroscopy experiments on a number of uniform turbid media with diffe rent 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 me asured parameters are the de intensity (I-dc), ac amplitude (1(ac)), a nd 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 o n the source-detector separation r. Our measurements show that the int ercepts of these straight lines predicted by the Green's function do n ot agree with the experimental results. To reproduce the experimental results, we have introduced an effective photon source whose spatial e xtent and source strength depend on the optical properties of the medi um. This effective source term has no effect on the slopes of the stra ight lines predicted by the Green's function at large values of r. (C) 1997 Optical Society of America