Value of t2-weighted magnetic resonance imaging early after myocardial infarction in dogs: comparison with bis-gadolinium-mesoporphyrin enhanced T1-weighted magnetic resonance imaging and functional data from cine magnetic resonance imaging
RATIONALE AND OBJECTIVES: Magnetic Resonance Imaging (MRI) has proved to provide noninvasive methods to investigate the functional repercussion of myocardial infarction and to measure infarct size with specific contrast agents. In this study, we evaluate whether the combination of T2-weighted and contrast-enhanced T1-weighted MRI could detect and discern necrotic and ischemic, but salvageable, myocardium. METHODS: Reperfused myocardial infarction was surgically induced in 14 dogs. T1- and T2-weighted MRI was performed 6 hours after administration of the necrosis avid contrast agent Gadophrin-2 at 0.05 mmol/kg. Gradient-echo cine MRI series were performed at baseline and at 6 hours. Quantification of myocardial infarction was performed with triphenyltetrazolium chloride staining. RESULTS: There was a strong correlation between of postcontrast T1-weighted MRI and histomorphometry (r2 = 0.98, P < 0.01). T2-weighted MRI overestimated the infarct size by 10.5% +/- 4.3% of left ventricular area. A good correlation was found between hyperintense areas on T2-weighted images and the percentage of dysfunctional areas on cine MRI (r2 = 0.84, P < 0.01). In regions with increased signal intensity on T2-weighted MRI, a decreased maximal systolic thickening (11.8% +/- 4.9%, P = 0.043) was found. CONCLUSION: In this study, the difference between the hyperintense areas on T2-weighted and enhanced T1-weighted images after myocardial infarction likely represents viable myocardium.