ELECTRICAL-IMPEDANCE TOMOGRAPHY - INDUCED-CURRENT IMAGING ACHIEVED WITH A MULTIPLE COIL SYSTEM

An experimental study of induced-current electrical impedance tomograp hy verifies that image quality Is enhanced by employing six rather tha n three induction coils by increasing the number of independent measur ements. However, with an increasing number of coils, the inverse probl em becomes more sensitive to measurement noise, Using 16 electrodes to measure surface voltages, it Is possible to collect 6 x 15 = 90 indep endent measurements. For comparison purposes, images of two dimensiona l conductivity perturbations are reconstructed by using the data for t hree and six coils with the truncated pseudoinverse algorithm, By sear ching for the optimal truncation index that minimizes the noise error plus the resolution error, the signal-to-noise ratio of the data acqui sition system was established as 58 db, Images obtained with this six- coil system reveal the sizes and locations of the conductivity perturb ations, This system also provides images within the central region of the object space, a capability not achieved in previous experimental s tudies using only three circular coils, Nevertheless, the three-coil s ystem can identify the conductivity perturbations near the periphery, However, it displays shifts in the locations and spread in the sizes o f perturbations near the center of the object.