Efficacy of sonothrombolysis using acoustically activated perflutren nanodroplets versus perflutren microbubbles

Abstract

Abstract Background The use of intermittent high mechanical index (HMI) ultrasound impulses in combination with intravenously administered microbubbles (MB) has been shown to dissolve arterial and microvascular thrombi. The recent development of liquid droplets with nanoscale diameter from commercially available microbubbles may optimize thrombus permeation and subsequent thrombus dissolution. Methods Thrombi were formed from fresh porcine arterial whole blood mixed with thrombin, and placed in a vascular system mimicking branching epicardial coronary circulation (Figure 1A) at 37 Celsius and flow rate. A diagnostic ultrasound system with a tissue mimicking phantom was placed on top of the thrombus to simulate transthoracic echocardiography. Thrombus treatment consisted of a 10-minute infusion of either diluted nanodroplets (ND) or MB (same concentration) with intermittent HMI fundamental multipulse (3 usec pulse duration; FUS) or single pulse harmonic (HUS) impulses. All treatments were randomized and compared with HMI impulses alone. Efficacy was evaluated by percentage thrombus dissolution (%TD). Transmission electron microscopy (TEM) of residual thrombi after treatment was performed to examine for droplet permeation and resultant formed microbubble size. Results A relatively monodisperse nanodroplets size distribution was formed from microbubble cooled compression (mean diameter was 147±54 nm). A total of 60 porcine arterial thrombi were tested, 20 in each MB and ND treated group (20 control). Overall, there was a significant difference in %TD between ND treated thrombi (combining HUS and FUS HMI treated groups) versus MB treated thrombi and control (p<0.0001 and p=0.02, respectively; ANOVA, Figure 1B). The highest %TD was seen in the FUS HMI treated ND group (mean 51±17%; Figure 1B). TEM of the DND treated group demonstrated significant expansion (diameters of 6 microns; Figure 1 C) of acoustically activated droplets embedded within the thrombi. Conclusion ND in combination with intermittent HMI ultrasound resulted in significantly greater thrombolysis compared to MB. In-vivo studies on nanodroplet mediated sonothrombolysis for vascular and microvascular thrombi should be performed with this modification of a commercially available microbubble. Figure 1 Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Theodore F. Hubbard Foundation