<title>Application of the finite element method for the forward model in infrared absorption imaging</title>

Abstract

Bedside instruments are now available which can transilluminate tissue with near-infrared radiation and measure the boundary flux both temporally and spatially resolved. Consequently there is an increasing demand for image processing methods that allow reconstruction of the spatial distribution of the absorption and scattering coefficient within the tissue. Iterative algorithms for solving this inverse problem require an accurate forward model. Previous attempts to simulate light propagation within a specific medium have been made either with a Monte-Carlo model or by deriving the Greens function for a given geometry, assuming diffuse light propagation. While the former requires extended computing time to achieve a certain precision, the latter is restricted to simple geometries. We present here a Finite Element model that allows the solution of the forward problem for complex geometries within a reasonable time and that could be used in real-time bedside imaging equipment. This model permits fast calculation of the integrated intensity and the mean time of flight. The model is being used to investigate perturbations imposed on the measurement data by absorbing or scattering inhomogeneities to determine the viability of the iterative reconstruction.