Nonlinearity of soft field in electrical impedance tomography system - Based on statistical methods

The nonlinearity in the electrical impedance tomography (EIT) system has been studied based on the graph method and the uniform design method. The nonlinearity degree is defined to analyze the case of two subareas with changed parameters in the circular area. The case of five factors at two levels is analyzed using normal and half-normal plots. The uniform design with eight factors at six levels is applied and the nonlinearity degree of the worst case is -93.265%. Images are reconstructed based on the bi-conjugate gradients method with the sensitivity matrix. The results show that, since the sensitivity matrix linearizes the nonlinear relationship between the change of electrical potential on the measuring electrodes and the change of the electrical conductivity in a subarea, and the coupling effect caused by the property of soft field in the EIT system is neglected, the image quality is low and the iteration time is uncertain. As the coupling effect exists between different subareas in the EIT system, though it can be partially compensated by limiting the iteration times, the iterative algorithms based on sensitivity matrix have their intrinsic limitations, and do not pertain to exact image reconstruction.