PHOTON MIGRATION THROUGH A TURBID SLAB DESCRIBED BY A MODEL-BASED ON DIFFUSION-APPROXIMATION .2. THEORY

The diffusion approximation of the radiative transfer equation is a mo del used widely to describe photon migration in highly diffusing media and is an important matter in biological tissue optics. An analysis o f the time-dependent diffusion equation together with its solutions fo r the slab geometry and for a semi-infinite diffusing medium are repor ted. These solutions, presented for both the time-dependent and the co ntinuous wave source, account for the refractive index mismatch betwee n the turbid medium and the surrounding medium. The results have been compared with those obtained when different boundary conditions were a ssumed. The comparison has shown that the effect of the refractive ind ex mismatch cannot be disregarded. This effect is particularly importa nt for the transmittance. The discussion of results also provides an a nalysis of the role of the absorption coefficient in the expression of the diffusion coefficient. (C) 1997 Optical Society of America.