Serial changes in nuclear magnetic resonance relaxation times after myocardial infarction in the rabbit: Relationship to water content, severity of ischemia, and histopathology over a six-month period

Abstract

To determine the serial changes in T₁ and T₂ relaxation times of myocardial infarction, and their relationship to observed changes in water content, regional myocardial blood flow, and histopathology, rabbits were studied at 14 time intervals ranging from 30 min to 6 months after coronary artery ligation. All values were compared to a control group. Hearts were subdivided into infarct and normal segments for measurement of blood flow, water content, and relaxation times (20‐MHz spectrometer); other hearts were excised intact for histopathologic studies. T₁ relaxation time of infarcted myocardium did not change significantly compared to control over the 6‐month study period. T₂ relaxation time increased (P < 0.0001) at 3 days and returned to baseline by 2 months. Consonant with the increase in T₂ of infarct, nuclear magnetic resonance (NMR) images at 3 days demonstrated an increase in signal intensity of infarct compared to surrounding normal myocardium. At 6 months, marked myocardial thinning was observed without changes in signal intensity. Changes in T₂ of infarcted myocardium were not related to changes in water content or seventy of ischemia, but correlated best with infarct healing and scar formation as detected on histopathology. In conclusion, the findings of this study indicate that T₂ relaxation time of the infarcted myocardium increases markedly at 3 days and remains elevated for 2 months. These changes correlate best with the onset and progression of infarct healing. These data demonstrate the potential of T₂‐weighted NMR imaging for assessing healing patterns following ischemic myocardial injury. © 1988 Academic Press, Inc.