Passive acoustic mapping of cavitation based on frequency sum and robust capon beamformer

Real-time dynamic monitoring of cavitation is essential for the safety and efficiency of high intensity focused ultrasound (HIFU) therapy. Passive acoustic mapping (PAM) has been proposed as a tool of monitoring HIFU therapy. Compared with standard B-mode imaging, PAM has the better detection sensitivity of cavitation. The performance of PAM algorithm is important for localization of cavitation and prediction of bubble-induced lesion. But the quality of cavitation images is hindered by poor resolution and interference of the conventional used PAM. In the present study, a unique PAM algorithm that combines frequency-sum beamforming with robust Capon beamformer (RCB) has been proposed to improve the image quality. The image resolution was improved by higher frequency information manufactured by a quadratic product of cavitation field, and the artifacts were suppressed by using RCB to reject interference among cavitation sources. The method was validated by simulations and in vitro experiments. The results suggested that the modified PAM can realize cavitation mapping with high spatial resolution and greatly reduced artifacts. Further improvements might be achieved with optimized fast imaging algorithm.