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Parameter sensitivity in near-infrared imaging

To model the photon migration in highly scattering media, we use an approximation of the Boltzmann equation, the diffusion equation. A prerequisite for handling the inverse problem consists in solving the forward problem under realistic conditions. We discuss the influence of boundary conditions on the light propagation. The boundary conditions at the walls surrounding the object highly sensitively influence the photon flux at the boundary which means that the time-resolved transmittance is affected. An algorithm for the determination of boundary parameters is introduced and demonstrated by an instructive example. We use the finite element method for the time-resolved case as a basic method in combination with a minimization strategy. The boundary conditions are determined as conditions of the third kind, i.e. the photon density is proportional to the outward photon flux at the boundary.