Passive acoustic mapping within the cranial vault during microbubble-mediated ultrasound brain therapy

Over the past 15 years, the use of passive sensor arrays combined with established beamforming algorithms to image acoustic activity during ultrasound therapies, so-called passive acoustic mapping (PAM), has been increasingly investigated for cavitation-based treatment monitoring and control purposes. Our group is interested in applications of microbubble-mediated ultrasound therapy in the brain, during which the skull bone presents unique challenges for both treatment delivery and acoustic emissions monitoring. We have demonstrated that skull-specific transcranial aberration correction methods can be applied during receive beamforming to augment PAM image quality through the skull bone, borrowing techniques developed originally for transmit beam focusing. Using custom clinical-prototype transmit/receive phased arrays, we have performed 3D microbubble imaging in vivo through ex vivo human skullcaps, and have exploited the resulting spatiotemporal cavitation information for real-time exposure level calibration and offline bioeffect distribution prediction. Ultrafast processing of acoustic emissions data can uncover cavitation dynamics hidden by conventional whole-burst temporal averaging, as well as inform temporal under-sampling strategies when millisecond-long tone bursts are applied. This talk will provide a historical overview of PAM for ultrasound therapy monitoring throughout the body, followed by a summary of recent progress made in mapping cavitation activity within the cranial vault during brain applications.