Abstract
Passive cavitation image (PCI) shows the power distribution of the acoustic emissions resulting from cavitation bubble collapses. The conventional PCI convolves the emitted cavitation signals with the point spread function of an imaging system, and it suffers from a low spatial resolution and contrast due to the increased sidelobe artifacts accumulated during the temporal integral process. To overcome the problems, the present study considers a 3-D time history of instantaneous PCIs where cavitation occurs at the local maxima of the main lobes of the beamformed cavitation field surrounded by the sidelobes largely spreading out in a time-space domain. A spatial and temporal gating technique was employed to detect the local maxima so that cavitation bubbles can be identified with their collapsing strength. The proposed approach was verified by the simulation for single and multiple cavitation bubbles, proving that it accurately detects the location and strength of the collapsing bubbles. An experimental test was also carried out for the cavitation bubbles produced by a clinical extracorporeal shock wave therapeutic device, which underpins that the proposed method successfully identifies every individual cavitation bubble.
Highlights
Cavitation bubbles are often generated in the biological media through which a high power ultrasound propagates
The acoustic signal can be sensed by using an ultrasonic probe employed in a conventional ultrasonic scanner to construct the spatial distribution of the acoustic emissions from collapsing bubbles, called passive cavitation image (PCI)
In this paper we propose a novel method that excludes the integration process so that it enables us to accurately identify collapsing cavitation bubbles and to measure their acoustic intensity
Summary
Cavitation bubbles are often generated in the biological media through which a high power ultrasound propagates. The micro-bubbles may be activated by ultrasound to open blood brain barrier(BBB) and to deliver drugs [12,13] Clinical ultrasonic therapy such as extracorporeal shock wave lithotripsy or therapy, high intensity focused ultrasonic surgery, histotripsy, and so on, makes use of the destructive effects resulting from violent inertial bubble collapses [16,17]. The acoustic signal can be sensed by using an ultrasonic probe employed in a conventional ultrasonic scanner to construct the spatial distribution of the acoustic emissions from collapsing bubbles, called passive cavitation image (PCI). PCI can be added up on clinical ultrasonic scanners and has an advantage of inexpensive real-time monitoring This imaging technique, unlike conventional ultrasonic imaging, does not transmit an interrogating active ultrasound to an imaging target and may not include a time gating process.
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