Robust Capon beamforming for passive cavitation mapping during high-intensity focused ultrasound therapy

A passive method that uses time exposure acoustics (TEA) to map inertial cavitation activity in real time during therapeutic ultrasound exposure was recently presented [Gyongy and Coussios, IEEE Trans. Biomed. Eng. 57, 48–56 (2010)]. While this approach provides sub-millimetric spatial resolution transversely to the high-intensity focused ultrasound (HIFU) beam, its axial resolution requires improvement. Furthermore, the TEA method is expected to have a lower overall resolution and diminished ability to reject interference and noise compared to an adaptive beamforming approach. To address these limitations, we propose the use of the adaptive, robust Capon beamformer (RCB), which has been previously shown in the context of active, 2-D ultrasound imaging to provide high resolution, good interference suppression, and robustness against steering vector errors. Using a multi-element tomographic cavitation sensor being developed for quality assessment of clinical HIFU transducers, the effectiveness of RCB is demonstrated for improved 3-D passive localization of inertial cavitation compared to TEA using simulated and experimental data.