Real-Time 3-D Passive Acoustic Mapping for Row-Column Arrays With the Cross-Spectrum Method

Real-time and 3-D monitoring of cavitation activity is critical for safe, effective, and controlled treatments in cavitation-based focused ultrasound (FUS) therapies. This 3-D monitoring capability is essential for detecting off-target cavitation events, particularly in at-risk structures and those occurring outside the plane of 2-D imaging. In this work, we demonstrate that using row-column arrays (RCAs) for 3-D passive acoustic mapping (PAM), which can be easily integrated into commercial ultrasound scanners compared to using hemispherical arrays or matrix arrays, represents a potent solution. For that, we propose the RCA-PAM method for image formation. This method deploys the angular spectrum (AS) method to back-propagate 3-D harmonic wave fields using the passively received cavitation signals by the RCA's row and column apertures, respectively. Then, the 3-D PAM volume is obtained by integrating the cross-spectrum of the two wave fields over a selected bandwidth. To further reduce image artifacts, we combine AS with dual-apodization with cross correlation (AS-DAX) for wave field propagation. Our experiments showed that RCA-PAM achieved 0.04±0.07 mm source localization error and comparable image quality to the ones reconstructed for the matrix array (same aperture size). We realized over 40 volumes/second reconstruction speed for a volume sized $128\,\times \, 128\,\times \,250$ voxels, using all frequency components in the RCA's working bandwidth. We also demonstrate the seamless combination of RCA-PAM and B-mode imaging using the same RCA for 3-D monitoring of MB cavitation activity in a mouse tumor model. In summary, the use of RCAs for cavitation monitoring represents a promising avenue to minimize treatment risks in cavitation-based FUS therapies.