Noninvasive Acoustoelectric Imaging of Resistivity Distribution Based on Lead Field Theory

Abstract

Acoustoelectric (AE) effect is a basic physical interaction that focused ultrasound that alters the resistivity at the focal spot. Exploiting the AE effect, noninvasive AE imaging (nAEI) of resistivity distribution is investigated based on lead field theory. According to lead field theory, measured AE signal is of good spatial position property, which is sifted by focused ultrasound. Therefore, nAEI can form images directly without resorting to the inverse algorithm. A uniform phantom, 15% NaCl solution, and a nonuniform phantom, composed of 15% NaCl solution and fat, are imaged and discussed. In the experiment, both stimulating and recording electrodes are noninvasive, fixed on the boundary of the imaging chamber. A 1-MHz focused ultrasound transducer scans across the imaging chamber to make spatial sifting. For the uniform phantom with the fixed focal spot, the linear relationship between measured AE signal envelope and injected current signal is tested. In addition, taking resistivity distribution into consideration, the $yz$ -section images of uniform and nonuniform phantoms are presented. Compared to that of the uniform phantom, the resistivity distribution interface of nonuniform phantom can be obviously imaged and distinguished, which is verified by ultrasound pulse-echo imaging. Also, the 3-D slice images confirm that, even taking injected current into consideration, nAEI is potential for resistivity distribution. Finally, the experiment results are discussed and the reason is analyzed from the aspect of enhanced ultrasound pressure and current density induced by resistivity distribution. Both experimental and simulation results validate the feasibility of nAEI of resistivity distribution, and this paper potentially enhances the application of nAEI for cancer detection.