Microvascular injury in reperfused infarcted myocardium: noninvasive assessment with contrast-enhanced echoplanar magnetic resonance imaging

Objectives. The purpose of this study was to measure the accumulation of labeled albumin and to visualize its distribution pattern in reperfused infarcted myocardium as function of time between onset of reperfusion and administration of the tracer. Background. Myocardial microvascular injury leads to leakage of albumin from the intravascular space. Quantitative measurements of GdDTPA-albumin with inversion recovery echoplanar imaging (IR-EPI) may allow noninvasive monitoring of microvascular injury. Methods. After 1 h of coronary artery occlusion, 56 rats were injected with GdDTPA-albumin or 123I-GdDTPA-albumin either immediately before reperfusion or image, 1 or 24 h after reperfusion. GdDTPA-albumin in blood, normal myocardium and reperfused infarction was dynamically measured with IR-EPI during 1 h postinjection (PI). Autoradiograms were obtained at 15 min PI. Accumulation of labeled albumin in myocardium was expressed as the ratio of myocardial to blood content. Results. In normal myocardium, the ratio of changes of relaxation rate-ratio (ΔR1-ratio) was 0.12 ± 0.01 and did not change over 1 h. In reperfused infarction, however, the ΔR1-ratio increased after administration. Animals given GdDTPA-albumin before reperfusion exhibited fastest accumulation (ΔR1-ratio 15 min PI: 0.56 ± 0.03) and essentially homogeneous distribution. The accumulation was slower when administered at image, 1 and 24 h after reperfusion (ΔR1-ratios 15 min PI: 0.39 ± 0.03; 0.31 ± 0.04; 0.16 ± 0.01; p < 0.001 compared to administration before reperfusion). Moreover, the tracer accumulated predominantly in the periphery of the injury zone. Conclusions. Amount and distribution pattern of labeled albumin in reperfused infarction are modulated by duration of reperfusion. The accumulation of GdDTPA-albumin can be quantified by IR-EPI. Thus, IR-EPI may be useful to noninvasively monitor myocardial microvascular injury in reperfused infarction.