Improved in vivo magnetic resonance imaging of acute myocardial infarction after intravenous paramagnetic contrast agent administration.

Gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA), a paramagnetic relaxation agent, has been used in vitro to improve the detection of acute myocardial infarction (MI) by magnetic resonance imaging (MRI). In this study, the ability of Gd-DTPA to improve in vivo magnetic resonance imaging of MI was examined. Ten dogs with MI caused by left anterior descending coronary artery ligation were imaged 1 to 5 days after infarction. Imaging was performed before and for 2 hours after intravenous administration of 0.34 mmol/kg Gd-DTPA. One to 2 days after MI, Gd-DTPA improved visualization of the infarct in 3 of 4 dogs. This effect was more prominent in dogs imaged 4 to 5 days after MI, when 6 of 6 dogs showed substantially improved infarct definition after Gd-DTPA. At both times the intensity ratio, an objective measure of contrast between infarcted and normal tissue that is defined by the ratio of image intensity of infarcted area to that of noninfarcted area, was significantly better after Gd-DTPA administration. The intensity ratio at 24 to 48 hours after infarction was 1.4 +/- 0.2 (mean +/- standard deviation) before Gd-DTPA, and 1.7 +/- 0.6 after Gd-DTPA (p = 0.03). The intensity ratio at 4 to 5 days after infarction was 1.5 +/- 0.3 before Gd-DTPA, and 1.8 +/- 0.5 after Gd-DTPA (p less than 0.001). Thus, Gd-DTPA administration improves in vivo visualization of MI by MRI.