No Access Submitted: 20 May 2016 Accepted: 05 August 2016 Published Online: 30 August 2016
The Journal of the Acoustical Society of America 140, 1374 (2016); https://doi.org/10.1121/1.4961364
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  • a)Electronic mail:

    b)Also at: Department of Urology, University of Washington School of Medicine, 1959 NE Pacific Street, Seattle, WA 98195.

    c)Also at: Department of Aerospace Engineering, University of Illinois at Urbana–Champaign, 1206 West Green Street, Urbana, Illinois 61801, USA.

View Contributors
  • Pooya Movahed
  • Wayne Kreider
  • Adam D. Maxwell
  • Shelby B. Hutchens
  • Jonathan B. Freund
A generalized Rayleigh–Plesset-type bubble dynamics model with a damage mechanism is developed for cavitation and damage of soft materials by focused ultrasound bursts. This study is linked to recent experimental observations in tissue-mimicking polyacrylamide and agar gel phantoms subjected to bursts of a kind being considered specifically for lithotripsy. These show bubble activation at multiple sites during the initial pulses. More cavities appear continuously through the course of the observations, similar to what is deduced in pig kidney tissues in shock-wave lithotripsy. Two different material models are used to represent the distinct properties of the two gel materials. The polyacrylamide gel is represented with a neo-Hookean elastic model and damaged based upon a maximum-strain criterion; the agar gel is represented with a strain-hardening Fung model and damaged according to the strain-energy-based Griffith's fracture criterion. Estimates based upon independently determined elasticity and viscosity of the two gel materials suggest that bubble confinement should be sufficient to prevent damage in the gels, and presumably injury in some tissues. Damage accumulation is therefore proposed to occur via a material fatigue, which is shown to be consistent with observed delays in widespread cavitation activity.
The authors are grateful for fruitful discussions with T. Colonius, K. Maeda, B. Dunmire, B. Cunitz, and M. Bailey. This work was supported by the National Institutes of Health (NIH) NIDDK Grant No. P01-DK043881.
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