title: MR imaging of experimental myocardial infarction.
abstract: The signal enhancement in MR imaging of normal, infarcted and reperfused myocardium was investigated using different types of contrast agents. To investigate the organ distribution of a macromolecular contrast agent, normal rats were imaged before, and serially after injection of dextran-(Gd-DTPA)15. Dextran-(Gd-DTPA)15 had an essentially intravascular distribution, and significantly enhanced various organs in normal rats, including the heart. There was a linear relationship between the injected dose and observed enhancement. To investigate myocardial signal enhancement, acute myocardial infarction was induced in pigs by ligating a coronary artery. In two groups of pigs, dextran-(Gd-DTPA)15 or Gd-DPTA was administered i.v. after approximately 4 h of occlusion. Imaging was performed repeatedly in vivo. The animals were sacrificed about 2-2.5 h after injecting the contrast medium. The hearts were excised and re-imaged ex vivo. In three other groups of pigs, imaging was only carried out on excised hearts with 6-hour-old infarctions (a) without injecting contrast medium, (b) with injection of Dy-DTPA-BMA 3 min before sacrifice, and (c) with injection of Gd-DTPA-BMA 2 h before sacrifice followed by injection of Dy-DTPA-BMA 3 min before sacrifice. Without contrast medium, the infarctions were visualized as regions with a high signal intensity in the proton density- and T2-weighted images of excised hearts. Injection of dextran-(Gd-DTPA)15 resulted in infarct visualization also in the T1-weighted images ex vivo, due to a pronounced enhancement in parts of the infarct periphery and moderate enhancement in normal myocardium. Gd-DTPA accumulated in the infarctions, resulting in a better infarct visualization in the T1- and proton density-weighted images of excised hearts, compared with the control and dextran-(Gd-DTPA)15 groups. In vivo, however, the infarctions could not be visualized either before or after injection of dextran-(Gd-DTPA)15 or Gd-DTPA. Injection of Dy-DTPA-BMA improved infarct visualization mainly in the proton density- and T2-weighted images of excised hearts, due to susceptibility-induced reduction of signal intensity in the nonischemic myocardium. With T2-weighting, the infarct visualization was markedly better in the Dy-DTPA-BMA group than in the controls, or in the dextran-(Gd-DTPA)15 and Gd-DPTA groups. The double-contrast technique yielded an excellent infarct visualization ex vivo in all sequences, superior to that obtained in all other groups of pigs, due to Gd-DTPA-BMA-induced enhancement of the infarctions combined with Dy-DTPA-BMA-induced reduction of signal intensity in normal myocardium.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Diagnostic Radiology, Uppsala University Hospital, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Wikström
mesh_terms: D000818:Animals; D003287:Contrast Media; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D009203:Myocardial Infarction / Q000175:diagnosis*; D051381:Rats; D011919:Rats, Inbred Strains; D013552:Swine
chemical_list: D003287:Contrast Media