Experimental justification for using 3D conductivity reconstructions in electrical impedance tomography

Conductivity imaging of the breast using electrical impedance tomography (EIT) is a three-dimensional (3D) problem since the induced currents are free to travel through the entire tissue volume. It is therefore necessary to determine the effect this 3D current flow has on the image reconstruction problem and to ascertain how much benefit is gained by using a more appropriate 3D model to estimate the conductivity distribution. In addition, it is important to consider how much is gained if measurements are collected from multiple circular arrays of electrodes positioned around the breast as opposed to just a single plane of electrodes. We used a 64 electrode EIT system to collect data from a series of high contrast saline phantoms to determine the benefits gained by using a 3D model and the incorporation of out-of-plane measurements. We found that it is preferable to use a 3D mesh even when looking only at a single plane through the object of interest and that this 3D mesh should extend in the axial direction at least one radius away from the plane of interest. Further, out-of-plane measurements enhance axial information and improve the quantification of reconstructed inclusions by a factor of 2.2 in the particular case presented here. These findings should ultimately be incorporated to clinical imaging with EIT when circular electrode arrays are employed.