Detection of heterogeneities within turbid media by time-gated transillumination: study based on the finite element method

摘要

The potentialities offered by time-gated transillumination of inhomogeneous tissue slab media are numerically investigated in this paper. A finite element model is firstly presented in order to solve the time-dependent light transport in mutiple-scattering optical media containing different embedded objects. The numerical procedure is based on the Galerkin formulation added to an implicite finite difference scheme (Backward Euler) to integrate the resulting matrix formulation with respect to time. The meshed domain refers to Cartesian-coordinates system (x,y) such that the computational grid can be adapted to scan along the longitudinal coordinate x. It takes into account the boundary conditions relative to air-tissue interfaces. The use of the method is demonstrated by the forward computations of time-gated intensities, resulting from line scans across either partially absorbing or scattering cylindrical objects. The overall computations confirm that time-gating technique is very sensitive to local variations in optical properties that are due to hidden objects in turbid media. It is also shown that the lateral localization of these inclusions is enhanced when the time-gate width (Δt) is decreased to about 30 ps.