BENEFITS OF REDUCING THE CARDIAC CYCLE-TRIGGERING FREQUENCY OF ULTRASOUND IMAGING TO INCREASE MYOCARDIAL OPACIFICATION WITH FSO69 DURING FUNDAMENTAL AND 2ND-HARMONIC IMAGING

Background: Recent work has shown significant enhancement in myocardia l contrast intensity with brief ultrasound pulsing gated to a discrete portion of the cardiac cycle over conventional 30 Hz imaging. We hypo thesized that limiting ultrasound imaging to less than every cardiac c ycle would further intensify the myocardial echo-contrast effect. We t herefore sought to determine the best pulsing frequency for ultrasound imaging to achieve optimal myocardial perfusion after the intravenous administration of FSO69 using fundamental and second harmonic imaging . Methods and Results: In 13 male mongrel dogs, myocardial contrast op acification was determined while varying the cardiac cycle-triggering frequency of ultrasound imaging after intravenous injections of FSO69. Resulting myocardial echo-contrast intensities with a cardiac cycle-t riggering frequency of every beat during end-diastole were compared wi th those with a cardiac cycle-triggering frequency of every third and fifth beat. Myocardial opacification, measured by background-subtracte d peak intensity and visual scoring, was significantly greater when ul trasound imaging was triggered to every third and fifth beats compared with every beat. These benefits a ere seen with imaging in both the f undamental and second harmonic modes. Optimal myocardial opacification with PSO69 was achieved with injections as low as 0.1 ml, a dose that produced significant acoustic shadowing in only 24% of the injections . The degree of myocardial opacification was not significantly affecte d when the images were acquired during end-systole or end-diastole. Co nclusions: Electrocardiogram-gated ultrasound imaging to every third o r fifth cardiac cycle greatly improves myocardial opacification compar ed with imaging each cardiac cycle. This benefit was increased twofold to threefold with the use of second harmonic imaging as compared with fundamental imaging.