Myocardial cavitational activity during continuous infusion and bolus intravenous injections of perfluorocarbon-containing microbubbles.

The 20-MHz component of broadband noise from inertial cavitation within the anterior myocardium of an open-chest dog was recorded during intravenous infusions or injections of perfluorocarbon-containing microbubbles during insonation with a 1.7-MHz harmonic transducer. Intramyocardial cavitational activity was evident even at a mechanical index of 0.2, but it increased significantly as frame rate and mechanical index were increased. The amount of myocardial contrast intensity produced by the microbubbles was increased by variables that reduced cavitational activity (eg, reducing frame rate to 1 every cardiac cycle or decreasing mechanical index). At a mechanical index of 0.2, myocardial contrast could still be observed at 10-Hz frame rates. These results confirm that intramyocardial cavitational activity is present during ultrasound imaging of microbubbles; imaging techniques that reduce cavitational activity increase the magnitude of myocardial contrast.