PURPOSE: To measure the fractional distribution volume of gadopentetate dimeglumine in normal and reperfused infarcted myocardium at magnetic resonance (MR) imaging by using the fractional distribution volume of technetium 99m–diethylenetriaminepentaacetic acid (DTPA) as an independent reference.

MATERIALS AND METHODS: Rats were subjected to 1 hour of coronary artery occlusion and 1 hour of reperfusion before inversion-recovery echo-planar imaging or autoradiography. Regional change in relaxation rate (ΔR1) ratios for myocardium over blood were compared with radioactivity ratios for myocardium over blood after the injection of ^99mTc-DTPA.

RESULTS: Both ΔR1 and radioactivity ratios demonstrated equilibrium distribution and hence represent partition coefficients (λ). The fractional distribution volumes were greater in infarcted myocardium (0.90 ± 0.05 for gadopentetate dimeglumine and 0.89 ± 0.04 for ^99mTc-DTPA) than in normal myocardium (0.23 ± 0.02 for gadopentetate dimeglumine and 0.16 ± 0.01 for ^99mTc-DTPA). Area at risk at autoradiography was not significantly 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 dimeglumine and ^99mTc-DTPA are similar and indicate extracellular distribution in normal 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 useful to quantify myocardial infarction.