MR Imaging of Gadolinium-DTPA-BMA-Enhanced Reperfused and Nonreperfused Porcine Myocardial Infarction

To investigate whether Gd-DTPA-BMA-enhanced MR imaging permits differentiation between reperfused and nonreperfused myocardial infarction, myocardial infarction was induced in 12 domestic pigs. In 6 pigs, Gd-DTPA-BMA, 0.3 mmol/kg b.w. was administered i.v. 60 min after the occlusion. In 6 other pigs, the infarctions were reperfused 80 min after the occlusion, followed by injection of Gd-DTPA-BMA after 20 min of reperfusion. Radiolabeled microspheres were used to confirm zero-flow during the occlusion period and reperfusion in the infarcted myocardium. All pigs were killed 20 min after injection of contrast medium, and the hearts were excised and imaged with MR. The Gd concentration was measured in infarcted and nonischemic myocardium by ICPAES. In the reperfused hearts, the infarctions were strongly highlighted, corresponding to a 5-fold higher Gd concentration in infarcted vis-à-vis nonischemic myocardium. In the hearts subjected to occlusion without reperfusion, there was only a rim of enhancement in the peripheral part of the infarctions.

MR Imaging of Double-Contrast Enhanced Porcine Myocardial Infarction

MR imaging was performed to investigate whether Gd-DTPA-BMA-induced contrast enhancement of myocardial infarction is counteracted by Dy-DTPA-BMA. Myocardial infarction was induced in 5 pigs. Microdialysate probes were inserted in ischemic and nonischemic myocardium. Gd-DTPA-BMA (0.3 mmol/kg b.w.) and Dy-DTPA-BMA (1.0 mmol/kg b.w.) were administered i.v. 4 hours post occlusion. The microdialysate was collected every 10 min and measured for Gd and Dy using inductively coupled plasma atomic emission spectrometry. The pigs were sacrificed 2 hours after administration of contrast media. The concentration of both contrast agents was 3 times higher in infarcted myocardium than in nonischemic myocardium. The infarctions displayed high signal intensity in spin-echo sequences ex vivo. This lack of detectable susceptibility effects from Dy may be caused by loss of cell membrane integrity in infarcted tissue as shown by our microdialysate and biopsy data.

Double-Contrast Enhanced Mr Imaging of Myocardial Infarction in the Pig

Myocardial infarction was induced by ligating a diagonal branch of the left anterior descending artery in 18 pigs. All pigs were sacrificed 6 h after the occlusion. Dysprosium diethylenetriaminepentaacetic acid bismethylamide (Dy-DTPA-BMA, 1.0 mmol/kg) was administered i.v. to 6 pigs, starting 3 min before sacrifice (injection time approximately 1 min). In a second group of 6 pigs, a double-contrast technique was used, consisting of an i.v. injection of gadolinium-DTPA-BMA (0.4 mmol/kg) 2 h before sacrifice, followed by an i.v. injection of Dy-DTPA-BMA (1.0 mmol/kg) 3 min before sacrifice. Six additional pigs, subjected to 6 h of coronary artery occlusion without administration of contrast medium, served as controls. The hearts were excised and imaged with MR. In the control animals, the infarctions demonstrated an increased signal intensity in the proton density- and T2-weighted images. Administration of Dy-DTPA-BMA primarily improved infarct visualization in the proton density- and T2-weighted images, due to reduction of signal intensity in nonischemic myocardium. The double-contrast technique further improved infarct visualization in all sequences.

Mr Imaging of Acute Myocardial Infarction in Pigs Using GD-Dtpa-Labeled Dextran

Myocardial infarctions were induced in 12 pigs. In 6 pigs, dextran-(Gd-DTPA)15 (≈0.1 mmol Gd/kg b.w.) was injected i.v. 4 to 4.5 hours after coronary artery occlusion. ECG gated MR images were obtained repeatedly before (n = 4) and after (n = 6) contrast medium injection. Relaxation times in blood samples were measured repeatedly. The animals were sacrificed 2 hours after contrast medium administration. The hearts were excised, reexamined in the MR equipment and stained with triphenyltetrazolium chloride (TTC) in order to define areas of infarction. The remaining 6 pigs were sacrificed 6 hours after occlusion without administration of contrast medium. These hearts were only imaged ex vivo. In vivo, the infarctions could not be identified with or without dextran-(Gd-DTPA)15. Ex vivo, without contrast medium, the infarctions had an increased signal intensity, most pronounced in the T2-weighted images. Dextran-(Gd-DTPA)15 caused a prolonged, pronounced shortening of T1 and T2 in blood samples. The infarct demarcation improved in the T1-weighted images after injection of dextran-(Gd-DTPA)15, due to a moderate enhancement in normal myocardium and a stronger enhancement at the periphery of the infarctions, while the central parts of the infarctions were only weakly enhanced.