Myocardial infarction quantification with late gadolinium-enhanced magnetic resonance imaging in rats using a 7-T scanner.

Aims: The objective of this study was to noninvasively measure the volume of myocardial infarction in rats, using delayed enhancement magnetic resonance imaging (MRI) in a coronary occlusion/reperfusion model on a 7-T scanner.

Methods: At 24 h after cardiac ischemia, contrast-enhanced MRI was performed. Two distinct experimental groups were compared: one was subjected to permanent ischemia (PL) and the other was subjected to 30 min of ischemia followed by 24 h of reperfusion (IR). The sizes of enhanced regions were compared to triphenyltetrazolium chloride (TTC)-stained sections of the excised rat heart. Cardiomyocyte apoptosis was analyzed by TUNEL methods, and neutrophils and macrophages were quantitated after histology and immunohistochemical staining.

Results: Twenty-four hours after ischemia, delayed hyperenhancement imaging was clearly visualized in the anterior left ventricular walls corresponding to the infarcted myocardium. In the PL group, infarct size was 37.2±9.8% (LV %) as measured by MRI and 38.8±9% (LV %) by TTC (P=NS). In the IR group, infarct size was 23.2±8.8% (LV %) as measured by MRI and 24.4±9.2% (LV %) by TTC (P=NS). Infarction volume measured with MRI was strongly correlated to TTC staining (R=0.82 for PL, R=0.973 for IR). Increased inflammatory cell infiltration was detected in the infarct area of the heart after reperfusion compared to permanent ligation (P<.01). The ratio of TUNEL-positive cardiomyocytes to total number of cardiomyocytes in the IR group was significantly reduced as compared to the PL group (P<.01).

Conclusions: MRI can accurately assess infarct size in intact rats early after MI. After transient arterial occlusion, the size of the myocardial infarct was found to be significantly smaller as compared to permanent occlusion.