We will design, construct and test a prototype of an adaptive electric current computed tomography (ECCT) system. This system will apply patterns of electric current through an array of electrodes on the surface of a body, and record the voltages that result on those electrodes. From these measured voltages, the system will then generate and display an approximate reconstruction of the electrical conductivity within that body. This reconstruction will provide an """"""""image"""""""" of the tissues in that body based on their differing electrical conductivities. This system is adaptive in the sense that the successive patterns of current applied to the body are determined from the previous voltage measurements and the optimization-reconstruction algorithm. We have shown that this method achieves a theoretically predicted maximum signal-to-noise ratio. Electric current computed tomography has many potential applications in clinical monitoring and basic biological research. Small changes in thoracic impedance result from pulmonary edema formation in adult respiratory distress syndrome. Greater spatial resolution and sensitivity of these changes will help resolve the uncertainty concerning interpretation of impedance measurements in terms of pulmonary edema. Prompt detection of pulmonary thromboembolus may also be feasible with this technique. Electrical impedance characterization of a bone fracture site and its electrical environment may permit more specific application of electrical stimuli to promote bone healing. Gastric secretion and gastric emptying are of interest in several pathological states, and preliminary studies suggest the use of impedance tomography in characterizing these functions. Electrical impedance may provide a temperature-sensitive dosimetry of tissues undergoing hyperthermic treatment for neoplasia. The present project will implement algorithms to model the presence of electrodes on the body surface to account for their effect in shunting the applied currents around rather than through the body being studied. A further innovation in the present approach is its use of 32 current generators and the simultaneous measurement of 32 voltages at the 32 active electrodes. This approach allows flexible programming of the current patterns applied to the unknown body. Full advantage of this flexibility is achieved by the use of the adaptive current algorithm which selects the optimal current pattern to apply based upon the observed unknown conductivities.
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