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.