Measurement of the distribution volume of gadopentetate dimeglumine at echo-planar MR imaging to quantify myocardial infarction: Comparison with Tc-99m-DTPA autoradiography in rats

PURPOSE: To measure the fractional distribution volume of gadopentetate dim eglumine in normal and reperfused infarcted myocardium at magnetic resonanc e (MR) imaging by using the fractional distribution volume of technetium 99 m-diethylenetriaminepentaacetic acid (DTPA) as an independent reference. MATERIALS AND METHODS: Rats were subjected to 1 hour of coronary artery occ lusion and 1 hour of reperfusion before inversion-recovery echo-planar imag ing or autoradiography. Regional change in relaxation rate (Delta R1) ratio s for myocardium over blood were compared with radioactivity ratios for myo cardium over blood after the injection of (TC)-T-99m-DTPA. RESULTS: Both Delta R1 and radioactivity ratios demonstrated equilibrium di stribution and hence represent partition coefficients (lambda). The fractio nal distribution volumes were greater in infarcted myocardium (0.90 +/- 0.0 5 for gadopentetate dimeglumine and 0.89 +/- 0.04 for Tc-99m-DTPA) than In normal myocardium (0.23 +/- 0.02 for gadopentetate dimeglumine and 0.16 +/- 0.01 for Tc-99m-DTPA). Area at risk at autoradiography was not significant ly different from that at histomorphometry. The infarction size defined by using triphenyltetrazolium chloride was 13% +/- 4 smaller than that defined by using autoradiography. CONCLUSION: The fractional distribution volumes of gadopentetate dimeglumin e and Tc-99m-DTPA are similar and indicate extracellular distribution in no rmal myocardium and intracellular as well as extracellular distribution in reperfused infarction. Because the failure of cells to exclude these agents is indicative of necrosis, contrast medium-enhanced MR imaging may be usef ul to quantify myocardial infarction.