Polar coordinate coherent passive acoustic beamforming for the modifiable improvement of image quality and field of view

Passive acoustic mapping (PAM) has been implemented for cavitation localization, quantification and detection in therapeutic ultrasound research. Having both imaging and therapy transducers coaxial would help move this purely laboratory technique close towards clinical use. In this study, a phased-array transducer was co-aligned in the middle of a single element HIFU transducer. Due to the limited imaging array dimension, the Cartesian coordinate PAM via phased-array may not suitable for cavitation monitoring. We propose a new coherent PAM in polar coordinates with the consideration of the monitoring field of view (FOV) and image quality. Results of cavitation monitoring experiments in tissue-mimicking phantoms illustrate that the proposed method, compared with the conventional PAM beamformer, keeps a same level of computation complexity (M*O(N)), while improved the noise area suppression by 90% - 96% and the image contrast ratio by 23 ± 2.3 dB. Moreover, the FOV of the proposed method is nearly twice of Cartesian coordinate beamforming output with the same computation time.