Abstract
Proton NMR spectroscopy at 7 Tesla (7T) was evaluated as a new method to quantify human fat composition noninvasively. In validation experiments, the composition of a known mixture of triolein, tristearin, and trilinolein agreed well with measurements by 1H NMR spectroscopy. Triglycerides in calf subcutaneous tissue and tibial bone marrow were examined in 20 healthy subjects by 1H spectroscopy. Ten well-resolved proton resonances from triglycerides were detected using stimulated echo acquisition mode sequence and small voxel (∼0.1 ml), and T1 and T2 were measured. Triglyceride composition was not different between calf subcutaneous adipose tissue and tibial marrow for a given subject, and its variation among subjects, as a result of diet and genetic differences, fell in a narrow range. After correction for differential relaxation effects, the marrow fat composition was 29.1 ± 3.5% saturated, 46.4 ± 4.8% monounsaturated, and 24.5 ± 3.1% diunsaturated, compared with adipose fat composition, 27.1 ± 4.2% saturated, 49.6 ± 5.7% monounsaturated, and 23.4 ± 3.9% diunsaturated. Proton spectroscopy at 7T offers a simple, fast, noninvasive, and painless method for obtaining detailed information about lipid composition in humans, and the sensitivity and resolution of the method may facilitate longitudinal monitoring of changes in lipid composition in response to diet, exercise, and disease.
Highlights
Proton NMR spectroscopy at 7 Tesla (7T) was evaluated as a new method to quantify human fat composition noninvasively
Ten lipid resonances are typically observed in the 7T 1H spectrum from physiological fats (Fig. 1)
Except for the double-bond protons, which partially overlap the methine proton of the glycerol backbone, the lipid resonances were wellresolved at 7T and qualitatively similar to high-resolution spectra obtained in mice [20]
Summary
Proton NMR spectroscopy at 7 Tesla (7T) was evaluated as a new method to quantify human fat composition noninvasively. Under high-resolution analytical conditions, signals from protons adjacent to double bonds are resolved, and it is a relatively simple matter to assess fat composition by 1H NMR spectroscopy [8,9,10,11,12] Extension of these methods to human applications is challenging because chemical shift resolution observed in vivo at 1.5 or 3.0 Tesla (T) is substantially worse than in analytical spectrometers. The fatty acid composition of mouse adipose tissue was reported based on 1H spectra obtained in vivo at 7T, where the chemical shift dispersion allows assignment of signals from protons adjacent to double bonds One advantage of this analysis [20] was the use of spectroscopic data from three adjacent resonances with a frequency bandwidth (BW) of only.
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