For some electrical impedance imaging problems an appropriate electrode geometry may be that of a square grid of electrodes on a surface plane. In this work, a sensitivity coefficient weighted filtered backprojection image reconstruction algorithm, previously developed for electrical impedance tomography (EIT) is applied to the problem of imaging a sub-surface plane. Following studies of the total sensitivity distributions and point spread functions given by various measurement strategies it is suggested that, for imaging in planes parallel to a surface grid of electrodes, it is advantageous to treat the electrode grid as two orthogonal sets of parallel linear arrays and to include measurements made between the ends of each array. Useful imaging performance at depth using this measurement strategy has been shown in simulation for a planar test distribution and with biomedical impedance data, and the robustness of the algorithm when used with incomplete data sets has been demonstrated.
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