Hadamard-encoded synthetic beamforming for high frame rate acoustoelectric current source imaging

Acoustoelectric (AE) imaging can potentially image the current source density (CSD) in biological systems using ultrasound with high spatial and temporal resolution. However, existing approaches are limited by poor signal-to-noise ratio (SNR) and low frame rate, as conventional focused-beam scanning requires many scan lines to cover a large field of view (FOV). Here, we present spatial encoding using Hadamard synthetic beamforming (HSB) for ultrafast AE imaging. HSB was implemented using 16 transmit events for each image frame. While this number of transmissions severely restricts the FOV in conventional focused-beam scanning, the same number of HSB transmissions sufficiently samples the aperture, enabling reconstructions limited only by the transducer geometry. We validate this approach using a 1.5D transducer array operating in real time at a center frequency of 0.6 MHz to image the CSD of single and multiple dipole current sources varying at 200 Hz in a bio-mimicking phantom at a frame rate of 500 Hz, demonstrating the potential for ultrafast AE imaging. Measurements demonstrate an expected ∼ 5 dB improvement in SNR compared to conventional focused-beam scanning after pressure equalization. The spatial resolution of HSB was comparable to that of the focused ultrasound beam, with fewer waveform artifacts observed at the same frame rate. Finally, imaging distributed current sources at various depths further demonstrated improved image quality using dynamic beamforming with HSB compared with conventional beam scanning at a fixed focal depth. These results demonstrate that HSB provides a practical and robust solution for ultrafast AE imaging of bioelectric currents.