Search

An electrical impedance tomography (EIT) system that uses the optimal current method to inject currents and the regularized Newton-Raphson algorithm to reconstruct an image of resistivity distribution is discussed. Iterative methods to derive the optimal current patterns through iterative physical measurements are developed. Direct methods to first determine the resistance matrix of a resistivity distribution through a set of current bases is injected and the measured voltage responses are stored. This permits iterative reconstruction techniques to operate on the stored data without requiring lengthy data taking from the object and reduces the effects of motion artifacts. The direct methods have superior performance as compared to the iterative methods in both optimal current and voltage generation. The results obtained with three sets of current bases are studied. >

We propose a measurement method using Walsh functions in 32-electrode electrical impedance tomography. By injecting currents in spatial Walsh function patterns, we use the simplicity of pulse type injection and yield the optimal SNR or distinguishability of sinusoidal injection. Once we measure boundary voltage data for the injection of all 31 patterns of Walsh functions, we can compute all 31 optimal current pattems. We can also synthesize the voltage data due to the injection of the optimal current patterns without actually injecting the optimal current patterns.

Static image reconstruction in electrical impedance tomopphy (EIT) using iterative algorithms requires a large computation time. We developed an improved NewtonRaphson (N-R) method which is more efficient, robust, and easily parallelizable. In order to check the feasibility of parallel computation in EIT, we implemented the algorithm on a parallel computer system. The results show a reduction in the computation time within a certain hiit as we increase the number of processors. We conclude that the improved N-R method is highly parallelizable and the use of parallel computers such as Transputers may solve the computational problems in static impedance imaging.

The use of compound electrodes to improve the conditioning and sensitivity of an electrical impedance tomography imaging system is described. Effects of electrode-skin contact impedance are discussed and a model is proposed. Reconstructed static images from phantoms are shown. >

A 32-electrode, 12-bit electrical impedance tomograph (EIT) which is capable of injecting optimal patterns of currents into an object to achieve maximum distinguishability is presented. The software for the system is described, and static images reconstructed from a circular 2-D phantom are shown. The EIT software consists of four parts: the interactive graphical finite-element mesh generator; the sparse linear system equation solver including node renumbering schemes; the calculation of the optimal patterns of injection current and the implementations of the EIT image reconstruction algorithms; and image display and postprocessing. >

An electrical impedance tomography (EIT) method is considered in which 32 electrodes are placed around the thorax, currents are injected, and voltages are measured to reconstruct a cross-sectional image of resistivity. The authors solve the forward problem using the finite-element method (FEM). The number of elements determines the spatial resolution of the resistivity image. An adaptive current-injection method to provide an optimal current distribution is used. The modified Newton-Raphson method is used as the reconstruction algorithm. The authors use sparse matrix techniques with node renumbering methods to minimize the computation time. >