Empirical model for target depth estimation used in the time-domain subsurface imaging.

Monte Carlo simulations were performed in order to obtain reflectance measurements from phantoms typically used in biomedical optics when either unpolarized or circularly polarized incident light is used. Phantoms contain spherical targets of different diameters, placed at different depths, with higher absorption than the surrounding medium, which are detected using a coaxial setup of laser and detector. The considered turbid media have highly anisotropic scattering phase functions, so detected light for the considered times of flight is not diffuse, but rather in the multiple-scattering regime. Therefore, the target reconstruction methods typically used in diffuse optical imaging cannot be employed. However, spatially resolved reflectance measurements in the time domain allow use of a novel reconstruction method based on the approximation of average photon trajectories, which are functions of the separation distance from the point of incidence and of the time of flight. With the approximated average photon trajectories, one can estimate the depth of the target.