Acoustic holograms for both therapy and monitoring transcranial ultrasound

When using holograms for cavitation-based therapeutic ultrasound, the acoustic focal spot may be misaligned with the passive cavitation detector (PCD) axis. We propose the use of 3-D-printed acoustic lenses for both therapeutic and monitoring systems. First, an acoustic hologram is designed to sharply focus the therapeutic beam at an arbitrary target into the skull. Then, a second hologram is designed for passive cavitation beamforming, i.e., to beamform the reception wavefront of the PCD with the target location, and in this way, cavitation emissions can be locally detected. Experiments with an ex vivo macaque skull and several blood vessel phantoms with microbubbles were conducted using a 500-kHz focused transducer and a confocal 3.5-MHz piezoelectric PCD. Results show that passive cavitation beamforming improves sensitivity and aligns the response of the PCD with a therapeutic focus located off-axis. The retrieved cavitation doses using this approach show a similar dynamic than for on-axis targeting setup. When compared to off-axis targeting, passive cavitation beamforming using holograms increases sensitivity to cavitation emissions, enabling precise, localized monitoring for therapeutic ultrasound. This method offers a cost-effective way to enhance the performance and monitoring of transcranial therapeutic ultrasound systems.