Methods for Dielectric Reconstruction in Microwave Tomography

In this paper an iterative electromagnetic time-domain inversion algorithm is described and modified to include a priori data of the shape and dielectric properties of an object being imaged. The algorithm is based on solving the regular and the adjoint Maxwell's equations in order to compute gradients, which are used to update the dielectric profile with the conjugate-gradient method. As an alternative a global optimisation algorithm, the particle swarm optimisation method, has also been investigated. The results show that by exploiting a priori dielectric data in this way a significant improvement in the resolving ability can be obtained. Finally Tikonov and edge preserving regularisation has been investigated and a modified regularisation scheme, supporting the a priori data is suggested.