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Pishchalnikov YA et al, 2011: Bubble proliferation in the cavitation field of a shock wave lithotripter

Pishchalnikov YA, Williams JC, McAteer JA
Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA


Abstract

Lithotripter shock waves (SWs) generated in non-degassed water at 0.5 and 2 Hz pulse repetition frequency (PRF) were characterized using a fiber-optic hydrophone. High-speed imaging captured the inertial growth-collapse-rebound cycle of cavitation bubbles, and continuous recording with a 60 fps camcorder was used to track bubble proliferation over successive SWs. Microbubbles that seeded the generation of bubble clouds formed by the breakup of cavitation jets and by bubble collapse following rebound. Microbubbles that persisted long enough served as cavitation nuclei for subsequent SWs, as such bubble clouds were enhanced at fast PRF. Visual tracking suggests that bubble clouds can originate from single bubbles.

J Acoust Soc Am. 2011 Aug;130(2):EL87-93. doi: 10.1121/1.3609920
PMID: 21877776 [PubMed - in process]
PMCID: PMC3195892 [Available on 2012/8/1]

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Comments 1

Othmar Wess on Friday, 02 September 2011 15:35

SWL at low pulse repetition frequency (PRF) (0.5 -1 Hz vs. 2 Hz or higher) turned out to be more effective in clinical routine treatment and is a recommendation for all operators to use slow PRF not higher than 1 Hz. Pishchalnikov et al. seem to have a sound explanation for this phenomenon. They give an experimental report on the interaction of shock waves fired into cavitation bubbles generated by previous shock waves. They could show that persisting bubbles of previous shock waves are turned into clouds of numerous smaller bubbles by following shock waves. These clouds serve as cavitation nuclei for subsequent shock waves and thus reduce shock wave energy delivered to the stone. Within 1.0 second (PRF 1Hz) most of the smaller bubbles are dissolved whereas this is not the case within 0.5 seconds. This may explain the clinical observation of higher fragmentation efficiency with low PRF´s. The study was performed in non-degassed water in vitro and it is not clear how well it matches real clinical treatment situations. However, similar effects are assumed to happen during clinical SWL.

Othmar Wess

SWL at low pulse repetition frequency (PRF) (0.5 -1 Hz vs. 2 Hz or higher) turned out to be more effective in clinical routine treatment and is a recommendation for all operators to use slow PRF not higher than 1 Hz. Pishchalnikov et al. seem to have a sound explanation for this phenomenon. They give an experimental report on the interaction of shock waves fired into cavitation bubbles generated by previous shock waves. They could show that persisting bubbles of previous shock waves are turned into clouds of numerous smaller bubbles by following shock waves. These clouds serve as cavitation nuclei for subsequent shock waves and thus reduce shock wave energy delivered to the stone. Within 1.0 second (PRF 1Hz) most of the smaller bubbles are dissolved whereas this is not the case within 0.5 seconds. This may explain the clinical observation of higher fragmentation efficiency with low PRF´s. The study was performed in non-degassed water in vitro and it is not clear how well it matches real clinical treatment situations. However, similar effects are assumed to happen during clinical SWL. Othmar Wess
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