Myocardial paramagnetic contrast agents for MR imaging

Several different paramagnetic contrast agents have been investigated for use in myocardial MR imaging. Gd-DTPA, the most extensively studied agent, has been shown to improve the conspicuity of acute myocardial infarcts on MR images in experimental animals and humans. However, this agent is limited as a marker of perfusion because of its rapid elimination by renal excretion and equilibration within the extracellular fluid space. Future investigation of Gd-DTPA as a myocardial perfusion agent may involve rapid-scanning techniques to define time-dependent accumulation of the contrast agent in normal and ischemic myocardium during the first pass after IV injection. Nondiffusable paramagnetic agents and agents with prolonged retention in myocardium are being studied actively, but further tests of toxicity and metabolism are needed before clinical trials. Additional macromolecular-bound metal chelates will be tested in the future. It is hoped that these agents will allow detection of the jeopardized region of myocardium in the setting of acute ischemia, before the onset of myocardial edema.