Cardiovascular nuclear magnetic resonance: basic and clinical applications

Abstract

Felix Bloch (1) at Stanford University and Edward Purcell and his colleagues (2) at Harvard University reported the phenomenon of NMR independently in 1946. As a result, Bloch and Purcell shared the 1952 Nobel Prize in Physics. Between 1950 and 1970, NMR spectroscopy was developed and used to analyze chemical and physical molecular structure. In 1971, Raymond Damadian reported that the NMR relaxation times of tumors differed from those of normal tissue, suggesting for the first time that magnetic resonance (MR) might be used for the detection of disease (3). In 1973, Paul Lauterbur was the first to report that images could be generated by NMR using small test tube samples of water and oil (4). Rather than creating a homogeneous magnet field by adjusting the "shimming" magnets to minimize field inhomogeneity, Lauterbur applied a magnetic field gradient to induce inhomogeneity in a planned way, providing a method to encode different parts of the substance to be imaged. He generated images using a technique analogous to that employed in x-ray computed tomography, known as back-projection-reconstruction. Two years later, Richard Ernst and colleagues proposed using the mathematical operation of Fourier transformation to create a spatial image from the frequencies generated by radiowave excitation within a magnetic field (5). It was an additional five years before Ernst and colleagues' ideas were applied, and they quickly formed the basis of most modern imaging techniques. Supposedly to avoid confusion with nuclear medicine, the clinical NMR imaging tool became known as magnetic resonance imaging (MRI) in the late 1970s. In 1977, Damadian and colleagues demonstrated MRI of the whole body (6). In this same year, Peter Mansfield developed the echo-planar imaging (EPI) technique for high-speed imaging (7). Also in that year, both Jacobus and colleagues (8) and Garlick and associates (9) published the first NMR phosphorus spectra from isolated perfused rat hearts, which paved the way for numerous publications on myocardial high-energy phosphate metabolism in the heart. In 1980 Goldman and his colleagues described the potential applications of NMR imaging in the assessment of the cardiovascular system (10). Many of the predictions made in that paper have gradually approached fruition. Despite the considerably more frequent use of cardiovascular MR (CMR) imaging compared with CMR spectroscopy, currently, there is significant clinical information to be ascertained from molecules in the myocardium that can be detected by clinical spectroscopy. This article will describe the state-of-the-art of imaging and spectroscopy and provide a framework for suggesting the future applications of this formidable technology. NMR spectroscopy and imaging techniquesThere are many approaches available, related to the sequence of radiofrequency pulses and magnetic field gradients, for the generation of clinical images and spectra by NMR. The trend has been toward faster imaging sequences and the reduction of artifacts, while spectroscopy develo...

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“…other integrated imaging techniques that aim toward a better understanding of metabolism, heart function, and the cardiovascular system (24).…”

MR imaging of the fetal heart

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“…1,2 At the same time, cardiac MRI was gaining importance as a useful adjunct for the assessment of the adult and pediatric cardiovascular system, with studies routinely able to deliver 3D angiography, myocardial characterization, cardiac chambers volumes, and vascular flow measurements. 3,4 However, ultrasound has remained the mainstay of fetal cardiovascular imaging, with initial attempts to explore the feasibility of cardiac MRI in fetuses hampered by the lack of a reliable electrocardiographic signal for cardiac triggering. [5][6][7][8] The appealing versatility of cardiac MRI has driven advances in imaging technology which have overcome some of the challenges associated with imaging the fetus, prompting an increasing number of groups to investigate the potential of this imaging modality for assessing fetal cardiovascular and placental pathophysiology.…”