Process for producing optimal current patterns for electrical impedance

Abstract

In electrical impedance tomography systems, the precision of voltage measurement is a critical factor in the results. Usually, the voltage values to be measured are limited by the necessity of limiting currents through the body to safe values. An effective method for increasing the apparent precision of the voltmeters is to use non-sinusoidal current patterns that produce the largest voltage variations in regions of most importance. This invention discloses several improvements in the methods by which the images resulting from any system of hardware that permits simultaneous injection of currents to all electrodes and voltage measurements at all electrodes, may be improved. One such improvement is a technique to find the shapes of the best current patterns to distinguish two different distributions of admittivity, conductivity, and permittivity in the region surrounded by electrodes. Another is a more complex procedure for finding the best shapes of the current patterns to best characterize an unknown pattern of admittivity, conductivity, or permittivity. Yet another is a procedure for calculating the values of voltages that would have been measured had sinusoidal sets of current been used, when actually using non-sinusoidal current patterns. This permits any standard reconstruction algorithm based on sinusoidal currents to be used with non-sinusoidal currents.