Acousto-Electrical Speckle Pattern in Lorentz Force Electrical Impedance Tomography

Lorentz Force Electrical Impedance Tomography (LFEIT) is a medical imaging technique of the tissue electrical impedance. It is based on the transmission of an ultrasound beam in a medium placed in a magnetic field, which induces an electrical current due to Lorentz force. The measurement of this current with electrodes allows to produce electrical impedance images with a spatial resolution close to ultrasound (US) imaging. The goal of this study is to assess the existence of an "acoustoelectric speckle" in the LFEIT technique, by similarity to the US speckle. In the first experiment, a 500 kHz transducer generates a 1 MPa peak pressure ultrasound wave on a gelatin phantom placed in a 300 mT magnetic field. The current measured by two electrodes is then compared to the US signal obtained in the same experimental conditions. The correlation coefficient of the two signals on the gelatin phantom was equal to 0.9279, indicating an excellent similarity. This similarity indicates the existence of an "acousto-electric speckle" in the LFEIT technique, with spatial characteristics driven by the acoustic parameters but related to electrical impedance inhomogeneities. These results give additional, non redundant information and suggest that speckle-based techniques used in US imaging could be applied.