Studies on Selective Imaging of Coronary Territories Using Intravenous Myocardial Contrast Echocardiography

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We clarified the relationship between the fragility of microbubble shell and the range of blood flow velocity in destroying the microbubbles regarding the completeness of destruction in a flow model study. In patients study, we propose to evaluate the left (LCA) and right coronary (RCA) territories separately in a session, because the entire myocardial segments are rarely opacified at one time. Microbubble destruction and replenishment principle was useful to determine the severity of coronary stenosis. In dog experiments, we visualized the left main coronary trunk (LMT) on a short axis image of aortic root while the short axis view or the long axis view of the left ventricle was visualized with another transducer. Insonation of LMT with continuous wave Doppler mode for the microbubble destruction and low power pulse inversion harmonic mode (real-time imaging) for perfusion imaging during infusion of BR1 was suitable to obtain appreciable images while microbubble destruction significantly affected the signal intensity in LCA territory. However, problems remained unsolved ; the only microbubble clinically available Levovist is too fragile and is not suitable for real-time imaging, and technical issue to handle two transducers simultaneously in a limited echo window.We further studied the safeness of microbubble destruction. We found that destruction of microbubbles in a microcirculation causes capillary rupture resulting in microhemorrhage leading to local infiltration of leukocytes. Then, we further studied this phenomena and found that microbubbles attach to the activated leukocytes and are phagocytosed, which provided the basis for ultrasonic imaging of inflammation. In addition, we found that thus recruited leukocytes (macrophages) produce vascular endothelial growth factor, thereby enhance angiogenesis.