INTERACTIONS BETWEEN MICROBUBBLES AND ULTRASOUND - IN-VITRO AND IN-VIVO OBSERVATIONS

Objectives. We attempted to examine the interactions between ultrasoun d and microbubbles. Background. The interactions between microbubbles and ultrasound are poorly understood. We hypothesized that 1) ultrasou nd destroys microbubbles, and 2) this destruction can be minimized by limiting the exposure of microbubbles to ultrasound. Methods. We perfo rmed in vitro and in vivo experiments in which microbubbles were inson ated at different frequencies, transmission powers and pulsing interva ls. Video intensity decay was measured in vitro and confirmed by measu rements of microbubble size and concentrations. Peak video intensity a nd mean microbubble myocardial transit rates were measured in vivo. Re sults. Imaging at lower frequencies and higher transmission powers res ulted in more rapid video intensity decay (p = 0.01), and decreasing e xposure of microbubbles to ultrasound minimized their destruction in v itro. Although these effects were also noted in vivo with venous injec tions of microbubbles, they were not seen with aortic root or direct c oronary artery injections. Conclusions. Ultrasound results in microbub ble destruction that is more evident at lower frequencies and higher a coustic powers. Reducing the exposure of microbubbles to ultrasound mi nimizes their destruction. This effect is most marked in vivo with ven ous rather than aortic or direct coronary injections of microbubbles. These findings could lead to effective strategies for myocardial perfu sion imaging with venous injections of microbubbles. (C)1997 by the Am erican College of Cardiology.