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We calculate the time-resolved flux of photons transmitted across an optically turbid slab containing a partially absorbing inclusion. An analytical expression is obtained for the flux at a detector positioned opposite a point source (at a distance equal to the thickness of the slab) when the center of the inclusion lies on the line connecting those points. The calculation employs a discrete-time lattice random-walk model of photon transport. The resulting expression is used to assess the affects of time resolution on the detectability of the inclusion. Key words: Random walks, optical imaging, detectability, optical contrast.

Monte Carlo simulations are used to discern scaling relationships for photon migration occurring within homogeneous, anisotropic scattering media of semi-infinite extent. Special attention is given to events associated with short path lengths. Empirical scaling relationships for path lengths and surface intensities are shown to agree with a consistency equation derived in an earlier study of anisotropic random walks. They are augmented here by a procedure that accounts for concomitant scaling of optical absorption coefficients. Results then are used to transform expressions that were obtained previously by analytical random-walk theory developed for an isotropic scattering model of photon migration. Quantities that are studied include the diffuse surface reflectance, the depth distribution of the fluence, and the time-resolved intensity of backreflected photons.

We describe a method for discriminating short- and long-path photons transmitted through a multiply scattering medium that is based on the relationship between the polarization states of the incident and forward-scattered light. Results of Monte Carlo simulations and experiments show that if the scattering anisotropy of the scatterers is sufficiently small, absorbing barriers embedded in optically dense suspensions of polystyrene spheres can be resolved with good contrast by selectively detecting a component of the scattered-light intensity that has preserved its incident circular polarization state. The principles of operation of a polarization-modulation system capable of measuring small polarization fractions are explained. Using this system we were able to measure polarized light in a depolarized background over 1000 times as large.