Abstract
We study the effect of optical anisotropy on the mean time-of-flight of photons
in a slab of turbid medium containing an inclusion whose optical properties
differ from those of the bulk. For this analysis the difference in the mean time
for a photon introduced into the slab to reach a specified target point with and
without the inclusion is calculated. This difference is defined to be a measure
of the contrast. The theoretical model is based on a continuous-time random
walk on a lattice, which can be solved exactly and furnishes an exact expression
for the contrast. Qualitative and quantitative characteristics of the contrast are
analysed as functions of the geometric configuration of the system components
(locations of the source, the inclusion and the detector), parameters that specify
the optical anisotropy of the medium, and either the scattering properties of the
inclusion or the lifetime of the small fluorophore in the case of the time-resolved
fluorescence experimental configuration.
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