Enhancing cavitation dynamics and its mechanical effects with dual-frequency ultrasound

Abstract

Objective. Acoustic cavitation and its mechanical effects (e.g., stress and strain) play a primary role in ultrasound applications. Introducing encapsulated microbubbles as cavitation nuclei and utilizing dual-frequency ultrasound excitation are highly effective approaches to reduce cavitation thresholds and enhance cavitation effects. However, the cavitation dynamics of encapsulated microbubbles and the resultant stress/strain in viscoelastic tissues under dual-frequency excitation are poorly understood, especially for the enhancement effects caused by a dual-frequency approach. The goal of this study was to numerically investigate the dynamics of a lipid-coated microbubble and the spatiotemporal distributions of the stress and strain under dual-frequency excitation. Approach. The Gilmore-Zener bubble model was coupled with a shell model for the nonlinear changes of both shell elasticity and viscosity to accurately simulate the cavitation dynamics of lipid-coated microbubbles in viscoelastic tissues. Then, the spatiotemporal evolutions of the cavitation-induced stress and strain in the surrounding tissues were characterized quantitatively. Finally, the influences of some paramount parameters were examined to optimize the outcomes. Main results. We demonstrated that the cavitation dynamics and associated stress/strain were prominently enhanced by a dual-frequency excitation, highlighting positive correlations between the maximum bubble expansion and the maximum stress/strain. Moreover, the results showed that the dual-frequency ultrasound with smaller differences in its frequencies and pressure amplitudes could enhance the bubble oscillations and stress/strain more efficiently, whereas the phase difference manifested small influences under these conditions. Additionally, the dual-frequency approach seemed to show a stronger enhancement effect with the shell/tissue viscoelasticity increasing to a certain extent. Significance. This study might contribute to optimizing the dual-frequency operation in terms of cavitation dynamics and its mechanical effects for high-efficient ultrasound applications.

On-demand regulation and enhancement of the nucleation in acoustic droplet vaporization using dual-frequency focused ultrasound

“…Dual-frequency excitation was utilized for cavitation-enhanced thermal ablation [21] , thrombolysis [22] , [23] , [24] , and sonodynamic therapy [25] , and was able to reduce the inertial cavitation threshold and improve therapeutic efficiency significantly. Numerical studies suggested the potential mechanisms for enhanced bubble cavitation by dual-frequency excitation, which include the unique nonlinear features of superharmonic focusing [26] , bubble oscillations [27] , the enhancement of the bubble expansion ratio and collapse strength [28] , the reduction of inertial cavitation threshold [29] , the increase mass transfer through the bubble interface [30] and the alteration of the bubble spherical stability [31] . However, these studies focused on the use of microbubbles rather than PFC nanodroplets.…”

Cavitation-induced pressure saturation: a mechanism governing bubble nucleation density in histotripsy

“…Although these parameters are adjustable in the design of the transducer, they are often limited by the acoustic window and depth of the target. Raising the ultrasound frequency increases density, but it also proportionately decreases bubble expansion, and thus it may be profitable to develop an advanced strategy whereby the bubbles are nucleated at high density by high frequency and further grown at low frequency to maximize both density and expansion (Li et al 2022, Edsall et al 2023. We did not examine the effect of waveform shape on density, but this has been found to further influence the growth and potential density of bubbles (Edsall et al 2023).…”

Resonance behaviors of encapsulated microbubbles oscillating nonlinearly with ultrasonic excitation

“…The radial oscillations of lipid-coated UCA microbubbles subjected to ultrasonic excitation were numerically simulated by solving the well-known Gilmore equation in the present study, since it has the largest applicability range with a high Mach number up to = 2.2, as compared to the widely used Rayleigh-Plesset and Keller-Miksis equations [46] . The Gilmore model is more suitable for the situations involving large-amplitude oscillations at relatively high acoustic pressures, especially in the microbubble-mediated therapeutic applications [47] , [48] . For a multi-bubble system, each bubble experiences additional driving pressures emitted by the nearby pulsating bubbles, hence the Gilmore equations were modified by considering the effects of the bubble–bubble interactions on the radial oscillations.…”