Volume 130, Issue 4, October 2011
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
130(2011); http://dx.doi.org/10.1121/1.3625239View Description Hide Description
Histotripsy is a therapy that focuses short-duration, high-amplitude pulses of ultrasound to incite a localized cavitationcloud that mechanically breaks down tissue. To investigate the mechanism of cloudformation, high-speed photography was used to observe cloudsgenerated during single histotripsy pulses. Pulses of 5−20 cycles duration were applied to a transparent tissue phantom by a 1-MHz spherically focused transducer.Clouds initiated from single cavitationbubbles that formed during the initial cycles of the pulse, and grew along the acoustic axis opposite the propagation direction. Based on these observations, we hypothesized that clouds form as a result of large negative pressuregenerated by the backscattering of shockwaves from a single bubble. The positive-pressure phase of the wave inverts upon scattering and superimposes on the incident negative-pressure phase to create this negative pressure and cavitation. The process repeats with each cycle of the incident wave, and the bubblecloud elongates toward the transducer. Finite-amplitude propagation distorts the incident wave such that the peak-positive pressure is much greater than the peak-negative pressure, which exaggerates the effect. The hypothesis was tested with two modified incident waves that maintained negative pressure but reduced the positive pressure amplitude. These waves suppressed cloudformation which supported the hypothesis.