Nuclear magnetic resonance imaging of acute myocardial infarction in dogs: alterations in magnetic relaxation times.

Nuclear magnetic resonance (NMR) imaging was used to study 24-hour-old acute myocardial infarctions in 8 dogs. Images and measurements of excised hearts were obtained in a 6.5 ml bore-resistive NMR imager (0.35 Tesla). Spin echo NMR imaging in each instance demonstrated the area of infarction as a region of increased signal intensity compared with that in normal myocardium. The T1 and T2 values of the area of infarction were greater than those of normal myocardium in all dogs. For each dog the T1 value was greater for the infarct region; however, the group mean value for T1 (ms) of the infarct region (728 +/- 94) was not significantly greater than that for the normal region (650 +/- 87). The T2 value (ms) was discriminate for all dogs, and the mean value for the infarct region (48 +/- 2) was significantly different (p less than 0.01) from the value for normal myocardium (42 +/- 1). The percent water content of the infarct (79 +/- 1%) was significantly greater (p less than 0.01) than that of normal regions (76 +/- 1%). The linear relationship between T2 value and percent water content showed a good correlation coefficient (r = 0.90; p less than 0.01). NMR imaging detects acute myocardial infarction as a positive image without contrast media. Increased signal intensity of the infarct is related to increased hydrogen density and increased T2 relaxation time.