Evaluation of myocardial perfusion using three-dimensional myocardial contrast echocardiography

The distribution of coronary blood volume is of fundamental importance to cardiac function. Previous investigators have demonstrated that myocardial vascular volume varies with both perfusion pressure and contraction. The purpose of this study is to measure vascular volume in an isolated rabbit heart model under a variety of controlled mechanical conditions using 3-D MCE. Isolated rabbit hearts were perfused with a room temperature crystalloid solution in a Langendorff perfusion apparatus and a small balloon was placed inside the left ventricle and attached to a volume infusion pump. Digital images of the heart were acquired with a Volumetrics 3D ultrasound scanner at perfusion pressures of 0, 30, and 50 mmHg without and with a microbubble-based contrast agent. LV pressure was held at a constant level of 0 mmHg. Regional videointensity and LV area were measured from short axis images in six hearts. Background-subtracted videointensity increased linearly with normalized coronary blood flow (R²=.99), demonstrating the ability of this method to noninvasively determine myocardial perfusion. Coronary vascular volume was estimated using a calibration technique and assuming the perfused myocardium may be modeled as a composite material, consisting of incompressible tissue and distensible vessels. Coronary volume was estimated to be 16-24% of the myocardium, comparable to values found in previous studies. Our method may be extended to noninvasively measuring regional coronary volume in patients, thereby providing an additional tool for physicians.