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Background —Because ischemically injured myocardium is frequently composed of viable and nonviable portions, a method to discriminate the two is useful for clinical management. Methods and Results —Ischemically injured myocardium was characterized with extracellular nonspecific (Gd-DTPA) and necrosis-specific (mesoporphyrin) MR contrast media in rats. Relaxation rates (R1) were measured on day 1 and day 2 by inversion-recovery echoplanar imaging. Spin-echo imaging was used to define contrast-enhanced regions and regional wall thickening. Gadolinium concentration, area at risk, and infarct size were measured at postmortem examination. ΔR1 ratio (ΔR1 myocardium /ΔR1 blood ) after administration of Gd-DTPA was greater in ischemically injured myocardium (1.20±0.15) than in normal myocardium (0.47±0.05, P <0.05), which was attributed to differences in gadolinium concentration and water content. The Gd-DTPA–enhanced region on day 2 was larger (32.8±0.9%) than true infarction as demonstrated by triphenyltetrazolium chloride (TTC) (24.6±1.4%, P <0.001, r =0.21). Bland-Altman analysis revealed that the Gd-DTPA–enhanced region overestimated true infarct size by 7.8±5.9%. On the other hand, the mesoporphyrin-enhanced region (26.9±1.8%, P =NS, r =0.87) and true infarct size were identical. The difference in the areas demarcated by the 2 agents is the peri-infarction. Systolic and diastolic MR images revealed no wall thickening in the mesoporphyrin-enhanced region (0.3±3.3%) but reduced thickening in the Gd-DTPA–enhanced rim (8.5±5.5%, P <0.05). Conclusions —The Gd-DTPA–enhanced region encompasses both viable and nonviable portions of the ischemically injured myocardium. The Gd-DTPA–enhanced area overestimated infarct size, but the mesoporphyrin-enhanced area matched true infarct size. The salvageable peri-infarction zone can be characterized with double-contrast–enhanced and functional MR imaging; the mismatched area of enhancement between the 2 agents shows residual wall thickening.
Saeed et al. (Tue,) studied this question.