The Inertial Cavitation Threshold in Soft Tissue Using a Dual-Frequency Driving Signal

Abstract

High Intensity Focused Ultrasound (HIFU) is a non-invasive technology that can be applied for treatment of different diseases and ablation of tumours in different parts of the body. When high intensity ultrasound propagates through the medium bubbles can be formed, a phenomenon known as acoustic cavitation. There are two different regimes of acoustic cavitation: stable cavitation when a bubble just oscillates around an equilibrium state, and inertial cavitation which is accompanied by bubble collapse. These two different regimes can be used for different biomedical applications. However, in some cases it can also make the treatment less predictable. Therefore, fundamental understanding of these effects is very important. In the current study theoretical investigation of the bubble dynamics in viscoelastic medium is performed and inertial cavitation thresholds have been calculated. To describe the bubble dynamics, Gilmore-Akulichev-Zener model has been used, which is suitable for a large bubble oscillations and high ultrasound powers. The results showed that using the dual-frequency driving signal the threshold value of inertial cavitation can be significantly reduced compared to single-frequency signal mode. Large difference between frequencies in the dual-frequency signal leads to lower threshold values. Numerical simulations also showed the dependencies of the cavitation threshold on the bubble radius.