Modified passive acoustic mapping with diagnostic-array angular response for cavitation monitoring during HIFU ablation in ex vivo tissue

Cavitation activity generated by high intensity focused ultrasound (HIFU) is one technique used in ultrasound therapy. Passive acoustic mapping (PAM) can be used for cavitation monitoring during ultrasound exposures to provide real-time feedback on the spatial location of suspected cavitation activity. Dedicated PAM beamforming techniques have been used for cavitation monitoring, and can be categorised as data-independent and data-dependent. Time exposure acoustics (TEA) is the conventional data-independent passive beamforming technique, but is limited by its susceptibility to noise artefacts. Data-dependent techniques, such as the robust capon beamformer (RCB), has been implemented with PAM to improve feature localization accurately. Moreover, angular response (AR) and/or the ultrasound field radiation pattern of the diagnostic array can have an impact on the image quality of ultrasound mapping. In this study, the AR factor was integrated into the RCB-based PAM beamformer to further improve its monitoring ability. This proposed PAM beamforming approach (AR-RCB) was tested on gel phantoms and ex vivo liver tissues during quasi continuous-wave (qCW) HIFU exposures, and was compared with two other beamfomers, TEA and RCB-based PAM.