The relationship between proton nuclear magnetic resonance relaxation parameters and myocardial perfusion with acute coronary arterial occlusion and reperfusion.

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Abstract
Previous investigators have demonstrated that acute myocardial ischemia, whether followed by reperfusion or not, is associated with prolongation of the proton nuclear magnetic resonance (NMR) relaxation times T1 and T2. Heretofore, the relationship between the severity of ischemia and alterations of these relaxation times has not been assessed. In our studies, changes in T1 and T2 were compared with myocardial perfusion in dogs both before and during 30 and 60 min of coronary arterial occlusion. In addition, studies were performed to assess the impact of reperfusion on relaxation times after 30 and 60 min of coronary occlusion. In the reperfusion studies the relationship between myocardial relaxation times and flow during the preocclusion, occlusion, and the 15 min reperfusion periods were studied. In the occlusion-only preparations, there was a significant inverse relationship between the relaxation times and flow during occlusion. In the reperfusion preparations there was a significant direct relationship between T1 and T2 and flow during the period of reperfusion. There was no significant relationship between the relaxation times and flow during occlusion in groups that subsequently underwent reperfusion, and no relationship between T1 and T2 and preocclusion flow in either the occlusion-only or reperfusion groups. These data suggest that the proton relaxation times provide an indication of the severity of an ischemic insult. Since NMR images can be generated that are sensitive to differences in these relaxation parameters, NMR imaging may provide a means to assess noninvasively the severity of the myocardial ischemic insult.