Combined high-speed NMR imaging of perfusion and microscopic coronary conductance vessels in the isolated rat heart

Noninvasive characterization of microcirculation at the level of both coron ary conductance and resistance vessels is of major importance for the under standing of microvascular adaptive processes in the heart. The objective of this study was to determine simultaneously myocardial perfusion and microv essel diameters in the myocardium by magnetic resonance (MR) imaging within the same heart. A MR imaging method is presented which combines high-resol ution perfusion measurement (140 X 140 mum(2)) by spin labeling with flow-w eighted MR microscopy of coronary microvessels (phi > 140 mum). We determin ed changes in myocardial perfusion and vessel diameters of isolated beating rat hearts (n = 10) at rest and during administration of nitroglycerin (0. 5 mg/min). Alterations in perfusion were validated by microsphere measureme nts. Under the influence of nitroglycerin an increase in perfusion (+2.51 /- 0.4 ml . min(-1) . g(-1), mean +/- SEM) and vessel diameters (+14.22 +/- 1.92%) could be observed. Endocardial perfusion revealed a modest enhanced susceptibility to nitroglycerin in comparison to epicardial perfusion. Ana lysis of vessels according to their diameters showed no significant differe nces. MR imaging allows the noninvasive and simultaneous determination of c onducting arteries and smaller resistance vessels in one and the same beati ng rat heart. Due to an excellent spatial resolution of these methods, tran smural characterization of both parameters at rest and during vasodilation is feasible. (C) 2001 Academic Press.