Myocardial Contrast Echocardiography

Abstract

contrast intravenous injection, microbubbles pass Myocardial contrast echocardiography (MCE) is an imaging modality to visualize myocardial perfusion using gas-filled microbubbles. Ultrasound contrast agents containing microbubbles are usually administered intravenously, and small microbubbles flow into left heart through pulmonary circulation. Number of microbubbles flowing into microcirculation would be very small, and image enhancing techniques such as intermittent power Doppler are required to detect weak signal from intramyocardial microbubbles. Fragile microbubbles are easily destroyed by incident ultrasound. When contrast agent is administered by continuous intravenous infusion, microbubbles are replenished into capillaries after microbubble destruction by ultrasound pulse. By analyzing the temporal recovery of myocardial contrast enhancement after microbubble destruction (a replenishment curve), myocardial blood flow could be determined. Such quantitative analysis can be performed using intermittent imaging technique or real-time MCE at low mechanical index (MI) ultrasound. MCE detects microvascular dysfunction (no-reflow phenomenon) in patients with acute myocardial infarction, which determines functional and clinical outcomes. MCE using stress testing could detect myocardial ischemia in patients with coronary artery disease (CAD). Theoretically, MCE could detect endocardial ischemia and diagnose CAD better than single-photon emission computed tomography (SPECT) because of higher spatial resolution. However, large-scale clinical studies failed to demonstrate superiority of MCE to SPECT for detecting CAD. No contrast agent is still approved for MCE, and further improvement of microbubbles and imaging techniques is required.