Control of Temporal Dynamics of Stable Cavitation by a Real-time Proportional Feedback Method

The objective of this work is to design an optimal controller to modulate the stable cavitation activity of microbubbles induced by pulsed ultrasound. During therapy, the microbubbles inflow the target region in the blood vessel, receive ultrasound exposure and produce cavitation activities, and then outflow the therapy region. The stability of the bubbles could be affected by acoustic pulses and flowing environment, leading to the decrease of bubble number and the nonuniformly temporal distribution of stable cavitation activity in the target region. Previous researches regulated peak negative pressure (PNP) to effectively control stable cavitation activity whereas some undesirable consequences (e.g. hemorrhage) were found after applying PNP regulation. We proposed a novel proportional feedback controller based on both PNP and pulse length (PL) regulation. In order to rapidly elevate stable cavitation intensity from baseline to the pre-expected level, in our controller, a proportional factor of P-1 was firstly used to real-time adjust PNP from the initial 0.01 MPa to an appropriate level of experiential stable cavitation range. The obtained PNP was fixed in the subsequent regulation, and another factor of P-2 was used to modulate PL from the initial 20 mu s to the obtained expected intensity and minimize the overshoot of the stable cavitation intensity P-3 was then applied to keep the temporal stability of stable cavitation activity (+/- 10% fluctuation range of the expected cavitation intensity) by further modulating PL. Finally, three parameters (rising time, stability ratio and concentration ratio) were used to evaluate the performance of the proposed method. Experimental results validated that the proposed method could control temporal distribution of stable cavitation intensity in the target region.