NONLINEAR RECONSTRUCTION CONSTRAINED BY IMAGE PROPERTIES IN ELECTRICAL-IMPEDANCE TOMOGRAPHY

It is proposed that image quality, for example the degree of roughness , in electrical impedance tomography is the essential measure required to regularize nonlinear reconstruction. Most previously published wor k has addressed efficiency, stabilization and speed of reconstruction and has overlooked the targeted image qualities. The measure of qualit y adopted is the mean square gradient of the logarithm of resistivity which, in combination with the chi(2) statistic as a measure of the fi t to the data, is minimized by iteration until convergence to a stable image is achieved. This penalty function is invariant to the scale of the resistivity and to the interchange of resistivity and conductivit y. The algorithm is tested on computer simulated data and on measureme nts from a cylindrical tank of electrolyte. The results demonstrate th e increased image definition that it would be possible to achieve as d ata acquisition systems are improved. The images show how a reduction in resolution can be traded for reduced noise artefacts, by selecting an appropriate target chi(2).