Use of MRI information to initialize the first stage of the image reconstruction algorithm in diffuse optical tomography

Abstract

We describe a method to increase the convergence speed for simultaneous reconstruction of absorption and scattering images in Diffuse Optical Tomography (DOT). We used the diffusion approximation of the radiative tranfer equation and the Finite Element Method (FEM) to solve the forward problem. The absorption and reduced scattering images were reconstructed by inverting the distribution of the moments of the time-dependent detected light flux. The inverse problem is solved with an optimization algorithm such as ART or Conjugate Gradient. This ill-posed inverse problem can be simplified by using <i>a priori </i>knowledge of the objects studied. In this paper, we consider that DOT is a functional imaging technique that can be complemented by an anatomical imaging technique such as Magnetic Resonance Imaging (MRI). The algorithm is built as follows: the first step consists in to dividing the observed zone into regions, thanks to another imaging technique such as MRI. In practice, this allows to adapt the mesh to the internal geometry. Then, supposing that each region is homogeneous absorption- and scattering-wise, a few parameters are reconstructed with an optimization technique. With a few iterative steps, well-averaged parameters can be obtained, which could be used to initialize the first stage of a global process. This process could reconstruct smaller inhomogeneities. We compare this method with direct global reconstruction, beginning with homogeneous parameters.