Spatiotemporal Passive Mapping of Cavitation in a Focused Acoustic Vortex Field

Vortex-based acoustic tweezer offer a novel particle manipulation method and has attracted extensive attention, its application potential in ultrasound therapies has begun to be exploited. Cavitation exerts a pivotal function in ultrasound therapies, the detection of its spatiotemporal evolution in the vortex field is of great significance for acoustic vortex-based ultrasound therapies. Ultrasound-based passive cavitation mapping has strong advantages over other methods in terms of cavitation detection, which is applicable to opaque media, can operate during acoustic irradiation, and allows spatial mapping. Here, we employ this method to spatially and temporally map cavitation of microbubbles in a focused acoustic vortex field and investigate its spatiotemporal evolution. The mapping results show that over time, multiple dispersed spots are observed in the time-series images and separation of lateral and axial distributions is observed in the spatiotemporal images. Further quantitative results show that the cavitation area tends to decrease with time, and the cavitation energy increases and then decreases with time. These observations can be ascribed to the microbubble aggregation induced by the acoustic vortex. The present work may be useful for understanding cavitation in acoustic vortex fields and for studying acoustic vortex-based ultrasound therapies.