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High-intensity, focused ultrasound therapy is a minimally invasive therapy technique that is effective and relatively safe. It can be used in areas including histotripsy, thermal ablation, and administering medication. Inertial cavitation is used to improve these therapy methods. The purpose of this study was to determine the effect of pressure amplitude on cavitation resonance frequency/bubble size at therapeutic field levels. Earlier work has indicated that the resonance size depends on pressure amplitude; however, the investigation only considered pressure amplitudes up to 1 MPa [1]. Our study was conducted by simulating the response of bubbles to linearly propagating sine waves using the Gilmore-Akulichev formulation to solve for the bubble response. The frequency of the sine wave varied from 1 to 5 MHz while the amplitude of the sine wave varied from 0.0001 to 9 MPa. The resonance size for a particular frequency of excitation and amplitude was determined by finding the initial bubble size that resulted in the maximum bubble expansion for an air bubble in water. The simulations demonstrated a downshift in resonance size with increasing pressure amplitude. Therefore, smaller bubbles will have a more dramatic response to ultrasound at therapeutic levels. KeywordsBubble dynamics, cavitation, therapeutics, high pressure, sound pressure Disciplines Biomedical | Biomedical Devices and Instrumentation | Electrical and Computer Engineering CommentsThe following article appeared in AIP Conference Proceedings 1113 (2009) Abstract High-intensity, focused ultrasound therapy is a minimally invasive therapy technique that is effective and relatively safe. It can be used in areas including histotripsy, thermal ablation, and administering medication. Inertial cavitation is used to improve these therapy methods. The purpose of this study was to determine the effect of pressure amplitude on cavitation resonance frequency/bubble size at therapeutic field levels. Earlier work has indicated that the resonance size depends on pressure amplitude; however, the investigation only considered pressure amplitudes up to 1 MPa [1]. Our study was conducted by simulating the response of bubbles to linearly propagating sine waves using the Gilmore-Akulichev formulation to solve for the bubble response. The frequency of the sine wave varied from 1 to 5 MHz while the amplitude of the sine wave varied from 0.0001 to 9 MPa. The resonance size for a particular frequency of excitation and amplitude was determined by finding the initial bubble size that resulted in the maximum bubble expansion for an air bubble in water. The simulations demonstrated a downshift in resonance size with increasing pressure amplitude. Therefore, smaller bubbles will have a more dramatic response to ultrasound at therapeutic levels..

High-intensity, focused ultrasound therapy is a minimally invasive therapy technique that has shown potential in many therapeutic applications, especially when coupled with the cavitation of microbubbles. The purpose of this study was to determine the effect of pressure amplitude on cavitation resonance frequency/bubble size at therapeutic field levels. Earlier work has indicated that the resonance frequency depends on pressure amplitude; however, the investigation only considered pressure amplitudes up to 1 MPa [Ultrasonics 43, 113 (2004)]. Our study was conducted by simulating the response of bubbles using the Gilmore-Akulichev formulation to solve for the bubble response. The frequency of the sine wave varied from 1–5 MHz while the amplitude of the sine wave varied from 0.0001–13 MPa. The resonance size for a particular frequency of excitation and amplitude was determined by finding the initial bubble size that resulted in the maximum bubble expansion relative to the initial size for an air bubble in water prior to the first collapse. Preliminary simulations indicated that this metric gave the correct resonance size for small excitations. These simulations demonstrated a downshift in resonance size with increasing pressure amplitude.

First and foremost and I would to acknowledge Dr. Timothy Bigelow. Through his intelligence and hard work he was rewarded a much deserved career grant that has been able to fund my graduate experience. He has challenged me and stretched my brain to places I did not think possible, and done so in the kindest most patient fashion. I am forever grateful. Special thanks to Charles Church (Associate Research Professor, University of Mississippi, Oxford, MS) for providing code that could be modified to calculate the bubble response. This work is supported by NSF grant Award ECCS-0643860 "CAREER: Ultrasound Histotripsy System Development to Improve Cancer Treatment." I would also like to thank Dr. Scott McClure in Veterinary Clinical Sciences. He kindly provided tissue samples for this study on demand.