High‐resolution ^H NMR spectral signature from human atheroma

Abstract

Coronary artery disease due to atherosclerosis takes the lives of approximately 550,000 Americans each year--an enormous toll. Put in economic terms, the cost to the United States alone has been estimated to exceed 60 billion dollars annually. We have found that well-resolved proton (1H) NMR spectra can be obtained from human atheroma (fatty plaque), despite its macroscopic solid appearance. The fraction of the total spectral intensity corresponding to the sharp 1H NMR signals is temperature dependent and approaches unity at body temperature (37 degrees C). Studies of the total lipids extracted from atheroma and cholesteryl esters were conducted to identify the chemical and physical origin of the spectral signature. The samples were characterized through assignment of their chemical shifts and by measurement of their T1 and T2 relaxation times as a function of magnetic field strength. The results suggest that the relatively sharp 1H NMR signals from human atheroma (excluding water) are due to a mixture of cholesteryl esters, whose liquid-crystalline to isotropic fluid phase transition is near body temperature. Preliminary applications to NMR imaging of human atheroma are reported, which demonstrate early fatty plaque formation within the wall of the aorta. These findings offer a basis for noninvasive imaging by NMR to monitor early and potentially reversible stages of human atherogenesis.

13C-NMR spectroscopy of human atherosclerotic lesions. Relation between fatty acid saturation, cholesteryl ester content, and luminal obstruction.

“…The slice corresponding to the central plane of the scanned plaque at the maximal stenosis site was dehydrated in paraffin. Sections 5 /xm thick were prepared from the paraffin-embedded slice and stained with a modified Masson's trichrome: the steps were (1) deparaffinization, (2) rehydration, (3) saturation in aqueous picric acid for 30 minutes, (4) rinsing in water, (5) Verhoeffs elastic staining for 6 minutes (3% hematoxylin, 100% ETOH, 2% ferric chloride hexahydrate, 4% potassium iodide with 2% iodine), (6) rinsing in water, (7) Biebrich scarlet-acid fuchsine staining for 3 minutes (0.5% aqueous Biebrich scarlet, 0.5% aqueous acid fuchsin, glacial acetic acid), (8) rinsing in water, (9) phosphotungstic acid 4% staining for 15 minutes, (10) light green 2% for 3 minutes, (11) differentiation in 1% acetic acid for 30 seconds, (12) dehydration, and (13) mounting with Permount.…”

Identification of cholesteryl esters in human carotid atherosclerosis by ex vivo image-guided proton MRS

“…It is important to note that previous NMR studies of atherosclerotic plaque lipid in human and animal models have employed the entire plaque specimen, rather than specific, selected regions (35,36). In addition to imageguided spectroscopy, another approach is chemical shift imaging (CSI), a form of spectroscopic imaging in which specific resonances can be selected and assigned a pixel intensity.…”

Mineral Volume and Morphology in Carotid Plaque Specimens Using High-Resolution MRI and CT

“…20,27,34 At least for the thresholding method, the comparison was with only the first echo (TEϭ9 to 10 ms) of a multiecho spin echo technique, which would minimize signal loss from susceptibility-induced gradients. However, longer TE se- quences incorporated into the k-means clustering approach may have had an effect in this regard.…”

“…18,25,26 However, there are other components of atherosclerotic plaque that may show decreased signal intensity on some or all pulse sequences; for example, solid cholesterol hydrate may be present and plaque lipids may exhibit T2 shortening secondary to liquid crystal behavior, depending on the lipid composition and cholesterol content. 20,27 Induced magnetic field inhomogeneities caused by differences in diamagnetic susceptibility between soft tissue and mineral may, in principle, lead to overestimation of mineral content on MRI. Alternatively, some forms of calcification or ossification could conceivably not appear dark on MRI.…”