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 i nfusions or injections of perfluorocarbon-containing microbubbles during in sonation with a 1.7-MHz harmonic transducer. Intramyocardial cavitational a ctivity was evident even at a mechanical index of 0.2, but it increased sig nificantly as frame rate and mechanical index were increased. The amount of myocardial contrast intensity produced by the microbubbles was increased b y variables that reduced cavitational activity (eg, reducing frame rate to 1 every cardiac cycle or decreasing mechanical index). At a mechanical inde x of 0.2, myocardial contrast could still be observed at 10-Hz frame rates. These results confirm that intramyocardial cavitational activity is presen t during ultrasound imaging of microbubbles; imaging techniques that reduce cavitational activity increase the magnitude of myocardial contrast.