Generalized two stream theory for photon migration

Recent work has indicated that a telegrapher's type equation may accurately describe the diffusion of photons in highly turbid media, specially during the ballistic regime of the process. On the other hand, calculations that have been made using the persistent random walk model (PRW) appear to contradict this result since the telegrapher's equation, for the case of very simple lattice geometries does not exist using PRW in 2 and 3 dimensions. In the present work we show how the continuous diffusion equations in 2D and 3D of PRW, in the weak coupling limit, provide an alternative theory for mesoscopic photon diffusion, showing that this problem can be studied using either the traditional telegrapher's equation or by the new approach provided by the continuum and discrete versions of PRW. (C) 1998 Elsevier Science B.V. All rights reserved