The Study of Subharmonics Generation Emitted from Micro-Bubble for Monitoring of HIFU Therapy

Cavitation bubbles have aroused mush attention for their significant promise in ultrasonic contrast imaging, targeted therapy and monitoring of high-intensity focused ultrasound (HIFU) therapy. In this paper, a model using a dual-frequency driving pressure for subharmonics generation from cavitation bubbles is constructed. By calculation of the Fourier transformation to the Keller-Milksis equation, we show that bubbles with appropriate radii produce significant subharmonic components within backscatter spectrum. In contrast to the case of single-frequency driving pressure, subharmonics at dual-frequency driving pressure can be generated for higher value of mechanical index (MI) and wider range of initial radii of bubbles. The subharmonic wave is not easy to be absorbed by soft tissues during its propagation compared with higher harmonic wave, and thus subharmonic mode-imaging method for monitoring HIFU therapy maybe has a potential application in providing proper signal-to-noise ratio.