Efficient generation of cavitation bubbles by dual-frequency exposure

Abstract

Microbubbles are known to enhance high intensity focused ultrasound (HIFU) treatment, which is a new cancer treatment method. Highly negative acoustic pressure can efficiently generate cavitation microbubbles, but it is difficult to obtain at the focus of HIFU because of nonlinear propagation. In our previous study, a “Dual-Frequency Excitation” method was suggested to synthesize waveforms emphasizing either the positive-peak-pressure or the negative-peak-pressure by superimposing the second harmonic onto the fundamental. In this study, four different type of dual-frequency exposure sequence at the fundamental frequency of 0.8 MHz were used, and the behavior of cavitation bubbles captured by a high-speed camera was compared. In the first and second sequences, the positive-peak-pressure emphasized (P) and negative-peak-pressure emphasized (N) waves were employed for 125 μs, respectively. In the third sequence, the N and P waves were employed in the earlier and later 62.5 μs, respectively, and they were exc...