MYOCARDIAL INFARCTION Imaging and characterization of acute myocardial infarction in vivo by gated nuclear magnetic resonance

Imaging by nuclear magnetic resonance (NMR) techniques has been shown to provide high-contrast resolution between soft tissues and characterization of normal and pathologic tissues by differences in magnetic relaxation times. The current study was designed to determine whether electrocardiogram (ECG)-gated NMR imaging of the canine heart in vivo could distinguish normal from infarcted myocardium without the use of intravenous paramagnetic contrast agents. Seven dogs were studied by ECG-gated NMR imaging in vivo (spin-echo technique) with a 0.35 Tesla superconducting magnet at 2 to 7 days after ligation of the left anterior descending coronary artery. In six of the seven dogs, signal intensity was increased in the anterior wall compared with the remainder of the left ventricle; this region of high signal intensity corresponded to the area of myocardial infarction demonstrated at postmortem examination. The signal intensity of the infarcted region was 66 + 27% greater than that of normal myocardium (p < .01). The T2 (spin-spin) relaxation time was 69 + 3% longer in the infarcted myocardium as compared with normal myocardium (p < .01). The NMR images from the seventh dog had uniform signal intensity throughout the myocardium of the left ventricle. An infarct was not evident on postmortem examination in this dog. Thus gated NMR imaging in vivo by the spinecho technique displays acute myocardial infarctions as regions of high signal intensity without the use of contrast media. The infarct is characterized by a prolonged T2 relaxation time. Circulation 69, No. 1, 125-130, 1984. TOMOGRAPHIC IMAGING of the hydrogen nucleus by proton nuclear magnetic resonance (NMR) techniques offers potential advantages for imaging the cardiovascular system. The lumen of blood vessels and the cardiac chambers display essentially no NMR signal by the spin-echo imaging technique' because of the high velocity of the protons in blood. This allows a high degree of signal contrast between moving blood and the walls of blood vessels and cardiac chambers without the need for intravenous paramagnetic contrast media. NMR imaging also offers the potential for characterization of tissues and biological fluids by Tl and T2 relaxation times, spin (hydrogen) density, and possibly spin-diffusion constants.4 From the Departments of Medicine and Radiology, University of California San Francisco Medical Center, San Francisco. Supported by grants CA 32850 from NCI, N0IHV0298 from NHLBI, and a grant from Diasonics, Inc. Address for correspondence: Charles B. Higgins, M.D., Department of Radiology, University of California San Francisco Medical Center, San Francisco, CA 94143. Received July 28, 1983; accepted Sept. 8, 1983. Dr. Botvinick is an Established Investigator of the American Heart Association and is supported in part by a grant from the George D. Smith Foundation, San Francisco. Vol. 69, No. 1, January 1984 Many pathologic processes, including acute myocardial infarction, are associated with an increased regional water content. -' Previous NMR spectrometric studies of tissue samples in vitro have demonstrated prolonged Tl relaxation times in infarcted myocardium relative to normal myocardium.5 6 Although an early report of experiments with hearts ex situ suggested that acute myocardial infarctions could be discriminated from normal myocardium only in the presence of a paramagnetic contrast medium,8 more recent reports suggest that infarcts can be detected without contrast media.9 " Previous investigations with proton NMR imaging in our laboratory have also demonstrated prolonged T I and T2 relaxation times of acutely infarcted skeletal muscle in the rat (in vivo)7 and in excised canine hearts with acutely infarcted myocardium." Both of these studies used the spin-echo imaging technique and found that the NMR signal intensity was perceptibly increased in the infarcted muscle as compared with normal muscle. The purposes of this study were to determine whether electrocardiogram (ECG)-gated proton NMR imaging could detect myocardial infarction without the use 125 by gest on Jauary 5, 2018 http://ciajournals.org/ D ow nladed from