Reperfused myocardial infarction as seen with use of necrosis-specific versus standard extracellular MR contrast media in rats

PURPOSE: To measure the difference in size of reperfused myocardial infarction with necrosis-specific (bis-gadolinium-mesoporphyrin [hereafter; mesoporphyrin]) and standard extracellular (gadopentetate dimeglumine) magnetic resonance (MR) contrast media. MATERIALS AND METHODS:Echo-planar (for T1 measurement) and spin-echo (for infarction size) MR imaging were conducted in 32 rats subjected to reperfused reversible (n = 16) and irreversible (n = 16) myocardial injuries. All animals received gadopentetate dimeglumine 1 hour after reperfusion and underwent imaging. Sixteen rats received mesoporphyrin at 2 hours, the other 16 rats received gadopentetate dimeglumine at 24 hours, and all animals underwent imaging at 24 hours. RESULTS: Mesoporphyrin produced prolonged (22 hours) reduction in T1 in irreversibly, but not in reversibly, injured myocardium. The size of the mesoporphyrin-enhanced region (37% +/- 4 [SEM] of left ventricular surface area) closely correlated with the true infarction size as measured by means of histomorphometry (36% +/- 3, r = 0.90). The size of the gadolinium-enhanced region overestimated (48% +/- 2 and 43% +/- 1 at 1 and 24 hours of reperfusion, respectively) the size of true infarction (36% +/- 3, P <.05, r = 0.02), but it was close to the size of the area at risk (r = 0.93). CONCLUSION: The sizes of hyperenhanced regions displayed by using mesoporphyrin and gadopentetate dimeglumine differed from each other. The difference in size of;he hyperenhanced region demarcated by mesoporphyrin and gabopentetate dimeglumine may provide an estimation of potentially salvageable myocardium.