V: Random Walk and Diffusion-Like Models of Photon Migration in Turbid Media

Abstract

The chapter focuses on the properties of multiply-scattering or turbid media, and emphasizes results obtained using random walk theory of photon migration in a turbid medium. Methodology based on the theory of random walks is a ubiquitous tool in the analysis of polymer configurations and is central to many of the techniques used to transform data taken from X-ray scattering experiments into useful structural parameters. The types of random walk models that are distinguished by the space in which the walk occurs include the continuum random walk and the lattice random walk. The chapter derives the joint probabilities required for translating optical data into physical parameters for a slab whose properties are homogeneous on a macroscopic scale. There are several approaches for modelling the use of optical techniques by random walk and/or diffusion theory to determine internal structure and inclusions in a multiply-scattering medium. Three categories of applications of the theory will be described (i) laser Doppler flowmetry, (ii) random walk results applied to spectroscopic methods, and (iii) the characterization of the performance of an optical imaging system.