Measurement of a 2D electric dipole field using the acousto-electric effect

Conventional methods for mapping cardiac current fields have either poor spatial resolution (e.g. ECG) or are time consuming (e.g., intra-cardiac catheter electrode mapping). We present a method based on the acousto-electric effect (AEE) and lead field theory for minimally-invasive mapping of 2D current distributions. The AEE is a pressure-induced conductivity modulation in which focused ultrasound can be used as a spatially-localized pressure source. As a proof of principle we generated a 2D dipole field in a thin bath of 0.9% NaCl solution by injecting 28 mA through a pair of electrodes. A 7.5 MHz transducer was focused on the bath from below. A recording electrode was rotated along the boundary of the bath in 20° steps. For each angle, the transducer was swept over the bath in a raster scan. A pulse-echo and an AEE voltage trace were acquired at each point. The AEE traces were combined in post-processing as if coming from a multi-electrode circular array. The direction and magnitude of the current field at each point in the plane was estimated from the AEE and compared to simulation. The potential field was independently mapped using a roving monopolar electrode. The correlation coefficient between this map and the simulated field was 0.9957. A current source density analysis located the current source and sink to within 1±2 mm of their true position. This method can be extended to 3 dimensions and has potential for use in rapid mapping of current fields in the heart with high spatial resolution.