Background-Gadophrin-2 is a new MRI contrast agent with high affinity for necrotic myocardium. The aim of the study was to evaluate whether noninvasive measurements of infarct size after thrombolysis are possible with gadophrin-2enhanced MRI. Methods and Results-Coronary artery thrombosis was induced in 3 groups of dogs by the copper-coil technique. Thrombolytic therapy together with aspirin and heparin was initiated after 90 minutes of occlusion. One day (group A), 2 days (group B), or 6 days

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... group C) after infarction, gadophrin-2 was injected intravenously (50 mol ⅐ kg Ϫ1 ). In vivo T1-weighted segmented turbo-FLASH, in vivo T2-weighted segmented half-Fourier turbo spin echo (HASTE), and T1and T2-weighted spin-echo MRI of the excised heart were performed 24 hours after gadophrin-2 injection. Regions of strong enhancement were observed on T1-weighted images. Planimetry of short-axis MR images and of corresponding triphenyltetrazolium chloride (TTC)-stained left ventricular (LV) slices showed a close correlation between the enhanced areas and TTC-negative areas for both in vivo ( r 2 ϭ0.98, PϽ0.0001; mean difference, 0.9Ϯ2.0% [SD] of the LV volume [LVV]) and postmortem (r 2 ϭ0.99, PϽ0.0001; mean difference, 0.9Ϯ1.4% of LVV) measurements. T2-weighted images overestimated the infarct size by 8.1Ϯ5.4% of LVV. The mean infarct size was 10.8Ϯ11.6% of LVV (group A), 22.4Ϯ11.7% (group B), and 5.1Ϯ9.3% (group C). Conclusions-In this animal model, in vivo gadophrin-2-enhanced MRI could precisely determine infarct size after thrombolytic therapy. This technique may be very useful for the noninvasive evaluation of infarct size after reperfusion for AMI. (Circulation. 1999;99:690-696.) Methods Experimental Model Dogs weighing 18 to 30 kg were sedated with xylazine (Rompun, Bayer AG), anesthetized with sodium pentobarbital (Nembutal,