It is proposed that image quality, for example the degree of roughness, in electrical impedance tomography is the essential measure required to regularise nonlinear reconstruction. Most previous published work has addressed efficiency, stabilisation, and speed of reconstruction and has overlooked the targeted image qualities. The measure of quality adopted is the mean square gradient of the logarithm of resistivity which, in combination with the chi squared statistic as a measure of the fit to the data, is minimised 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 conductivity. The algorithm is tested on computer simulated data and on measurements from a cylindrical tank of electrolyte. The results demonstrate the increased image definition that it would be possible to achieve as data 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 squared.
