Dependence of Cavitation Bubble Size on Pressure Amplitude at Therapeutic Levels

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 Wa [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..