Closed-loop Spatiotemporal Control of Microbubble Dynamics
Safe, effective therapies mediated by microbubble oscillations (acoustic cavitation) require real-time methods to control the amplitude and type of microbubble oscillations and ensure that cavitation occurs within the desired region. Due to the highly nonlinear and stochastic nature of acoustic cavitation, such methods pose a major scientific challenge.
We recently proposed a novel real-time controller that is based on fast passive acoustic imaging that uses specific frequency bands of the microbubble acoustic emissions (harmonic, ultra-harmonic, etc.) to control cavitation activity. This work made the following contributions: i) demonstrated temporal control of microbubble dynamics (within 10 % of tolerance), ii) showed that spatial control of cavitation activity, when cavitation existed simultaneously in multiple regions, is possible, and iii) demonstrated improved sensitivity and robustness of the controller across a range of conditions (noise level, bubble concentration, etc.). Considering the challenges involved in controlling the microbubble dynamics, providing the ability to fine-tune their type of oscillation and within the desired region can have significant implications for therapy.
|Real-time control of microbubble oscillations. The applied FUS pressure (bottom left) is adjusted according to the measured level of the third harmonic (orange, top left). Levels are computed from the passive acoustic maps formed from the bubbles’ harmonic emissions (top right). The size and direction of step are determined based on the measured level compared with the expected level at that pressure, based on a control law (bottom right). [Patel et al. IEEE T. Biomed. Eng. 66(7) (2019)]