NMR relaxation times in acute myocardial infarction: relative influence of changes in tissue water and fat content.

Tissue changes known to occur with acute myocardial infarction include increases in tissue water and lipid content. We sought to evaluate the relative contribution of alterations in tissue water and fat content to the changes of T1 and T2 relaxation times with infarction. Nine mongrel dogs underwent coronary artery occlusion for 6-12 h. T1 and T2 at 20 MHz and tissue water and fat content of normal and infarcted tissue were measured. Tissue water content, T1, and T2 were significantly greater in infarcted myocardium compared to normal (P less than 0.05). Tissue fat content, while not significantly different, increased linearly in infarcted samples as a function of duration of ischemia (r = 0.77). Despite this increase in fat content, only tissue water content was significantly linearly related to T1 (r = 0.97) and T2 (r = 0.91). Increases in T1 and T2 of infarcted tissue appeared to be most significantly influenced by changes in tissue water content. While total tissue fat content increased with duration of ischemia, it did not appear to significantly alter T1 or T2.