The use of the boundary element method in the forward problem of electrical impedance tomography

With the forward problem of Electrical Impedance Tomography (EIT) the conductivity distribution of an object and the positions of the injecting electrodes are given. The potential distribution at the surface is to be computed. When the object consists of a set of nested compartments with constant conductivity the Boundary Element Method (BEM) can be used in these computations. The authors´ aim is to develop a parametric model of these compartments and fit this model to the measured potentials. In such an inverse method the BEM has to be applied on each iteration and therefore an efficient implementation of the BEM is required. Here the trade-off between speed and accuracy of the BEM is explored. It is found that with 64 discretization points the potential distribution caused by 16 combinations of current injection in a two compartment model can be computed in 3 s with an accuracy of 1%. Furthermore, it is found that with a simple model of the torso, the potentials are much more sensitive to geometrical variations in the lungs than to the aorta