The evolution and monitoring method of cavitation activity under focused ultrasound
High intensity focused ultrasound is widely used in clinical non-invasive treatment of tumors.Real-time monitoring of cavitation activities during ultrasound treatment is of great significance to ensure the safety and effectiveness of treatment.In this study,a passive cavitation detection and driving power monitoring system for bionic tissue phantom and isolated bovine liver tissue under focused ultrasound was established.The development process of bubbles and damage in the phantom during ultrasound was monitored by microscope,and the correlation between bubble developing processes and cavitation characteristic signal changes was analyzed.The experiment shows that there is no increase in the amplitude of broadband noise before the boiling bubbles are generated during the ultrasonic irradiation of the phantom under 150 W electric power.Boiling bubbles are generated in the phantom at 6 s,after its rupture,a large number of cavitation nuclei are generated and cavitation bubble groups are formed,the broadband noise amplitude begins to increase,and then the bubble group gradually develops towards the transducer.When the bubble group stops developing to the transducer,the tiny bubbles near the transducer gradually merge to generate boiling bubbles,and the inertial cavitation intensity gradually decreases under the shielding of boiling bubbles.The generation and breaking of boiling bubbles will lead to large fluctuations in driving power and amplitudes of harmonics in the backscattering signal synchronously.In isolated bovine liver tissue,the occurrence time of boiling cavitation gradually advanced with the increase of sound intensity.The experimental results show that the generation and rupture of boiling bubbles will promote the occurrence of inertial cavitation.Therefore,under the irradiation of focused ultrasound with different intensities,severe cavitation activity can be avoided by adjusting the irradiation time.
High intensity focused ultrasoundCavitation effectPassive cavitation detectionDriving powerBoiling cavitation
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