Dynamic simulation and optimization of the inertial cavitation threshold under dual-frequency ultrasound

Microbubbles, or contrast agents, are regularly applied in the field of biomedical ultrasound. Their unique acoustic properties, e. g. the nonlinear characteristics of their harmonic responses, coalescence and cavitation effects enabled their applications in contrast imaging, ultrasound stimulation, drug delivery, molecular imaging, et al. Multiple experimental researches have proved cavitation threshold could be lower using dual-frequency. Yet, they are not well correlated with the theory. This paper explores bubble dynamics under excitations of dual-frequency combinations, and comprehensively compares three bubble simulation models: Rayleigh-Plesset model, Keller-Miksis model and Gilmore-Akulichev model. The Gilmore-Akulichev model is further explored for MHz range frequencies and combined with Zener model considering the viscoelastic effect of the medium. The optimal inertial cavitation threshold could be found for different initial bubble radii at certain dual-frequencies. Dual-frequency could significantly reduce the cavitation threshold compare to single-frequency. This study provides a possible route for optimizing ultrasound excitations for initiating inertial cavitation.