SUBSURFACE ELECTRICAL-IMPEDANCE IMAGING USING ORTHOGONAL LINEAR ELECTRODE ARRAYS

The main limitation of electrical impedance tomography as an imaging m odality is its inherently poor spatial resolution. Although more infor mation about the impedance distribution within an object can be retrie ved by the use of larger numbers of surface electrodes, the additional information tends to relate to regions of the object close to the ele ctrodes rather than at depth. The paper describes the application of a n image reconstruction approach originally developed for medical elect rical impedance tomography to the alternative problem of mapping elect rical impedance distributions in a subsurface volume. The use of this geometry allows the chosen imaged plane to be approximately uniformly sensed by a surface grid of electrodes leading to uniform resolution i n the image and the possibility of exploiting the relatively high reso lution information available at shallow depths. The advantage of the u se of an electrode grid, treated as two orthogonal sets of parallel li near arrays, is demonstrated and the behaviour of the point-spread fun ction in planes parallel to the surface plane examined. The applicatio n of a spatial frequency filter to counteract reconstruction blur is d escribed. Simulated reconstructions of subsurface structures and an ex ample biomedical image are presented.