Dynamic assessment of dual-frequency microbubble-mediated sonothrombolysis in vitro

Optimizing the use of high intensity focused ultrasound (HIFU) for recanalization of occluded blood vessels is an actively researched area. This yields an alternative therapy to the use of thrombolytic drugs in the treatment of ischemic stroke. HIFU treatment, used in conjunction with microbubbles (MBs) in the fluid stream, serves to augment the dissipation of the blood clot. In this study, using an in vitro approach, we implement a flow system to simulate the dynamic dispersion of blood clots using single-frequency focused ultrasound (SFFU) and dual-frequency focused ultrasound (DFFU). The effects of permutations of acoustic power and driving frequency (SFFU vs. DFFU) on the rate of disintegration and site-specific lytic action are quantified under the influence of fluid akin to that in a blood vessel, for specific microbubble concentrations. It is found that dual-frequency excitation in general produces a faster rate of clot dissipation in comparison to single-frequency excitation, and this observation is corroborated by cavitation signal detection. Our observations indicate that accelerated thrombolysis may be realized by the inertial cavitation threshold of DFFU being lower than that of SFFU. Furthermore, the thrombolytic effect with variance in microbubble concentration is studied for a fixed acoustic power. The efficacy of DFFU is not found to vary appreciably with an increase in microbubble concentration from 10 ⁸ MBs/ml to 10 ⁹ MBs/ml, possibly due to acoustic shadowing induced at increased concentrations.