The complete electrode model for imaging and electrode contact compensation in electrical impedance tomography

Electrical Impedance Tomography (EIT) is an imaging modality which currently shows promise for the detection and characterization of breast cancer. A very significant problem in EIT imaging is the proper modeling of the interface between the body and the electrodes. We have found empirically that it is very difficult, in a clinical setting, to assure that all electrodes make satisfactory contact with the body. In addition, we have observed a capacitive effect at skin/electrode boundary that is spatially heterogeneous. To compensate for these problems, we have developed a hybrid nonlinear-linear reconstruction algorithm in which we first estimate electrode surface impedances, using a Newton-type iterative optimization procedure with an analytically computed Jacobian matrix. We subsequently make use of a linearized algorithm to perform a three-dimensional reconstruction of perturbations in both contact impedances and in the spatial distributions of conductivity and permittivity. Results show that, using this procedure, artifacts due to electrodes making poor contact can be greatly reduced.