Performance of a transcranial US array designed for 4D acoustoelectric brain imaging in humans

Noninvasive electrical brain imaging in humans suffers from poor spatial resolution due to the uncertain spread of electric fields through the head. To overcome this limitation, we propose 4D transcranial Acoustoelectric Brain Imaging (tABI) based on the acoustoelectric effect for mapping current densities at a spatial resolution confined to the ultrasound (US) focus. This study describes the performance of a custom 0.6 MHz 2D US array designed for tABI through the adult human skull. Time-varying current was injected between two electrodes in 0.9% saline to produce a dipole at well-controlled current densities. A distant recording electrode was placed in the saline bath to detect the AE signal as the US beam was electronically steered in 3D near the dipole. At each beam position, a burst of US pulses was delivered to reconstruct the time-varying current. The AE amplitude was measured with and without an adult human skull and at different current amplitudes. The AE signal could be detected at depths greater than 40 mm from the surface of the skull. Sensitivity for detecting the AE signal through bone was 1.47μV/(MPa*mA/cm
²
). The noise equivalent current densities normalized to 1 MPa were 1.3 and 1.8 mA/cm
²
with and without the skull, respectively. Further optimization of ABI instrumentation and beamforming may push the detection limit towards small neural currents through thick skull and, perhaps, lead to a new noninvasive modality for real-time electrical brain imaging in humans.