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• W2164183759 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. 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. Adipose mass and the anatomic distribution of adipose tissue strongly influence the risk of multiple diseases. The fatty acid composition of adipose tissue may also influence predisposition to various disorders including cancer (1Simonsen N. van't Veer P. Strain J.J. Martin-Moreno J.M. Huttunen J.K. Navajas J.F. Martin B.C. Thamm M. Kardinaal A.F. Kok F.J. et al.Adipose tissue omega-3 and omega-6 fatty acid content and breast cancer in the EURAMIC study. European Community Multicenter Study on Antioxidants, Myocardial Infarction, and Breast Cancer.Am. J. Epidemiol. 1998; 147: 342-352Crossref PubMed Scopus (136) Google Scholar, 2Shannon J. King I.B. Moshofsky R. Lampe J.W. Li Gao D. Ray R.M. Thomas D.B. Erythrocyte fatty acids and breast cancer risk: a case-control study in Shanghai, China.Am. J. Clin. Nutr. 2007; 85: 1090-1097Crossref PubMed Scopus (102) Google Scholar), type 2 diabetes (3Storlien L.H. Higgins J.A. Thomas T.C. Brown M.A. Wang H.Q. Huang X.F. Else P.L. Diet composition and insulin action in animal models.Br. J. Nutr. 2000; 83: 85-90Crossref Google Scholar, 4Manco M. Greco A.V. Capristo E. Gniuli D. De Gaetano A. Gasbarrini G. Insulin resistance directly correlates with increased saturated fatty acids in skeletal muscle triglycerides.Metabolism. 2000; 49: 220-224Abstract Full Text PDF PubMed Scopus (141) Google Scholar, 5Storlien L.H. Jenkins A.B. Chisholm D.J. Pascoe W.S. Khouri S. Kraegen E.W. Influence of dietary fat composition on development of insulin resistance in rats. Relationship to muscle triglyceride and omega-3 fatty acids in muscle phospholipid.Diabetes. 1991; 40: 280-289Crossref PubMed Google Scholar, 6Meyer K.A. Kushi L.H. Jacobs Jr., D.R. Folsom A.R. Dietary fat and incidence of type 2 diabetes in older Iowa women.Diabetes Care. 2001; 24: 1528-1535Crossref PubMed Scopus (313) Google Scholar), and heart disease (7Hu F.B. Willett W.C. Optimal diets for prevention of coronary heart disease.J. Am. Med. Assoc. 2002; 288: 2569-2578Crossref PubMed Scopus (1165) Google Scholar). Nevertheless, the relations among adipose tissue composition and the risk of disease are controversial and difficult to study, in part because of the traditional requirement for invasive biopsy. Noninvasive analysis of fat composition in humans by 1H NMR spectroscopy would have major advantages, because the study could be integrated into routine exams. Under high-resolution analytical conditions, signals from protons adjacent to double bonds are easily resolved, and it is a relatively simple matter to assess fat composition by 1H NMR spectroscopy (8Zancanaro C. Nano R. Marchioro C. Sbarbati A. Boicelli A. Osculati F. Magnetic resonance spectroscopy investigations of brown adipose tissue and isolated brown adipocytes.J. Lipid Res. 1994; 35: 2191-2199Abstract Full Text PDF PubMed Google Scholar, 9Miyake Y. Yokomizo K. Matsuzaki N. Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy.J. Am. Oil Chem. Soc. 1998; 75: 1091-1094Crossref Google Scholar, 10Guillen M.D. Ruiz A. 1H nuclear magnetic resonance as a fast tool for determining the composition of acyl chains in acylglycerol mixtures.Eur. J. Lipid Sci. Technol. 2003; 105: 502-507Crossref Scopus (100) Google Scholar, 11Knothe G. Kenar J.A. Determination of the fatty acid profile by 1H-NMR spectroscopy.Eur. J. Lipid Sci. Technol. 2004; 106: 88-96Crossref Scopus (347) Google Scholar, 12Yeung D.K.W. Lam S.L. Griffith J.F. Chan A.B.W. Chen Z. Tsang P.H. Leung P.C. Analysis of bone marrow fatty acid composition using high-resolution proton NMR spectroscopy.Chem. Phys. Lipids. 2008; 151: 103-109Crossref PubMed Scopus (45) Google Scholar). However, 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. Because of the intense current interest in triglyceride composition and metabolism, several alternatives have been suggested, including selective detection of polyunsaturated fatty acids in animal models at 4.7 T (13Lunati E. Farace P. Nicolato E. Righetti C. Marzola P. Sbarbati A. Osculati F. Polyunsaturated fatty acids mapping by 1H MR-chemical shift imaging.Magn. Reson. Med. 2001; 46: 879-883Crossref PubMed Scopus (39) Google Scholar), two-dimensional NMR at 3 T (14Velan S.S. Durst C. Lemieux S.K. Raylman R.R. Sridhar R. Spencer R.G. Hobbs G.R. Thomas M.A. Investigation of muscle lipid metabolism by localized one- and two-dimensional MRS techniques using a clinical 3T MRI/MRS scanner.J. Magn. Reson. Imaging. 2007; 25: 192-199Crossref PubMed Scopus (34) Google Scholar), and 1H-decoupled 13C NMR spectroscopy (15Beckmann N. Brocard J.J. Keller U. Seelig J. Relationship between the degree of unsaturation of dietary fatty acids and adipose tissue fatty acids assessed by natural-abundance 13C magnetic resonance spectroscopy in man.Magn. Reson. Med. 1992; 27: 97-106Crossref PubMed Scopus (26) Google Scholar, 16Dimand R.J. Moonen C.T. Chu S.C. Bradbury E.M. Kurland G. Cox K.L. Adipose tissue abnormalities in cystic fibrosis: noninvasive determination of mono- and polyunsaturated fatty acids by carbon-13 topical magnetic resonance spectroscopy.Pediatr. Res. 1988; 24: 243-246Crossref PubMed Scopus (17) Google Scholar, 17Moonen C.T. Dimand R.J. Cox K.L. The noninvasive determination of linoleic acid content of human adipose tissue by natural abundance carbon-13 nuclear magnetic resonance.Magn. Reson. Med. 1988; 6: 140-157Crossref PubMed Scopus (64) Google Scholar, 18Thomas E.L. Frost G. Barnard M.L. Bryant D.J. Taylor-Robinson S.D. Simbrunner J. Coutts G.A. Burl M. Bloom S.R. Sales K.D. et al.An in vivo 13C magnetic resonance spectroscopic study of the relationship between diet and adipose tissue composition.Lipids. 1996; 31: 145-151Crossref PubMed Scopus (29) Google Scholar, 19Hwang J.H. Bluml S. Leaf A. Ross B.D. In vivo characterization of fatty acids in human adipose tissue using natural abundance 1H decoupled 13C MRS at 1.5 T: clinical applications to dietary therapy.NMR Biomed. 2003; 16: 160-167Crossref PubMed Scopus (39) Google Scholar). The large chemical shift dispersion of 13C is a major advantage compared with 1H observations. Wide application, however, is limited by the requirement for additional coils and a second radiofrequency channel. Chemical shift resolution in the 1H spectrum should, in principle, improve at higher fields. Recently, 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 (20Strobel K. van den Hoff J. Pietzsch J. Localized proton magnetic resonance spectroscopy of lipids in adipose tissue at high spatial resolution in mice in vivo.J. Lipid Res. 2008; 49: 473-480Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar) was the use of spectroscopic data from three adjacent resonances with a frequency bandwidth (BW) of only 0.74 ppm (221 Hz at 7T). In other reports (8Zancanaro C. Nano R. Marchioro C. Sbarbati A. Boicelli A. Osculati F. Magnetic resonance spectroscopy investigations of brown adipose tissue and isolated brown adipocytes.J. Lipid Res. 1994; 35: 2191-2199Abstract Full Text PDF PubMed Google Scholar), triglyceride saturation was determined from the olefinic protons (-CH = CH-, at ∼5.31 ppm) by using the CH3 methyl protons (at ∼0.90 ppm) as the reference. These two resonances span a frequency range of 4.41 ppm (1,314 Hz at 7T). The wide BW may result in less-uniform excitation profiles, and the use of frequency-dependent spatial localization yields spectra with resonances originating in different physical locations, an artifact known as chemical shift displacement. The ability to noninvasively monitor triglyceride composition using proton spectroscopy would have wide applications in clinical research. In this study, the approach described by Strobel, van den Hoff, and Pietzsch (20Strobel K. van den Hoff J. Pietzsch J. Localized proton magnetic resonance spectroscopy of lipids in adipose tissue at high spatial resolution in mice in vivo.J. Lipid Res. 2008; 49: 473-480Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar) to measuring fatty acid composition by 1H NMR spectroscopy in mice was tested in phantoms and extended to healthy human subjects. The fatty acid composition of bone marrow measured by NMR in this study was in good agreement with some (12Yeung D.K.W. Lam S.L. Griffith J.F. Chan A.B.W. Chen Z. Tsang P.H. Leung P.C. Analysis of bone marrow fatty acid composition using high-resolution proton NMR spectroscopy.Chem. Phys. Lipids. 2008; 151: 103-109Crossref PubMed Scopus (45) Google Scholar) but not all (21Lund P. Abadi D. Mathies J. Lipid composition of normal human bone marrow as determined by column chromatography.J. Lipid Res. 1962; 3: 95-98Abstract Full Text PDF Google Scholar) reports of fatty acid composition by gas chromatography. The NMR determination of saturated fatty acids in extremity subcutaneous fat agreed well with gas chromatographic analysis of abdominal subcutaneous fat, about 27% of fatty acids. Somewhat lower values for monounsatured fats, about 50%, were found by NMR, compared with 57% found in biopsy studies. The principles used by numerous investigators to quantify fat composition by 1H NMR (8Zancanaro C. Nano R. Marchioro C. Sbarbati A. Boicelli A. Osculati F. Magnetic resonance spectroscopy investigations of brown adipose tissue and isolated brown adipocytes.J. Lipid Res. 1994; 35: 2191-2199Abstract Full Text PDF PubMed Google Scholar, 9Miyake Y. Yokomizo K. Matsuzaki N. Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy.J. Am. Oil Chem. Soc. 1998; 75: 1091-1094Crossref Google Scholar, 10Guillen M.D. Ruiz A. 1H nuclear magnetic resonance as a fast tool for determining the composition of acyl chains in acylglycerol mixtures.Eur. J. Lipid Sci. Technol. 2003; 105: 502-507Crossref Scopus (100) Google Scholar, 11Knothe G. Kenar J.A. Determination of the fatty acid profile by 1H-NMR spectroscopy.Eur. J. Lipid Sci. Technol. 2004; 106: 88-96Crossref Scopus (347) Google Scholar, 12Yeung D.K.W. Lam S.L. Griffith J.F. Chan A.B.W. Chen Z. Tsang P.H. Leung P.C. Analysis of bone marrow fatty acid composition using high-resolution proton NMR spectroscopy.Chem. Phys. Lipids. 2008; 151: 103-109Crossref PubMed Scopus (45) Google Scholar, 20Strobel K. van den Hoff J. Pietzsch J. Localized proton magnetic resonance spectroscopy of lipids in adipose tissue at high spatial resolution in mice in vivo.J. Lipid Res. 2008; 49: 473-480Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar) are easily extended to human studies at 7T, where high-quality 1H NMR spectra can be obtained routinely. The protocol was approved by the Institutional Review Board. Informed consent was obtained from all participants prior to the study. Twenty healthy adults (twelve females and eight males) age 22–52 years (average 34 years; without diabetes or known vascular disease) were studied supine or prone in a 7T system (Achieva, Philips Medical Systems, Cleveland, OH). Spectra were acquired with a partial-volume quadrature transmit/receive coil customized to fit the shape of a human calf. Axial, coronal, and sagittal T2-weighted turbo spin echo images were initially acquired of the left calf muscle. Typical parameters were: field of view 180 × 180 mm, repetition time (TR) 1,500 ms, echo time (TE) 75 ms, turbo factor 16, and number of acquisitions (NA), 1. Single-voxel stimulated echo acquisition mode (STEAM) (typical parameters: voxel size 5 × 5 × 5 mm3 (∼0.1 ml), TR 2,000 ms, TE 20 ms, spectral BW of 4 kHz, number of points (NP) 4,096 and zero-filled to 8,192 prior to Fourier transform, NA 16, no water suppression) was used to acquire 1H spectra from tibial bone marrow and subcutaneous fat tissue. To correct individual resonances for relaxation effects, T1 and T2 were measured in seven of the subjects. T1 was measured using inversion-recovery, with nine inversion delay times in the range of 5 ms to 3,000 ms, with TR 7 s and TE 40 ms. T2 was measured by using ten TE values from 20 ms to 180 ms, with TR 8 s. Subjects were instructed to move slowly in the scan room. The entire scanning session was 60 min or less and it was well-tolerated by all subjects. All subjects were interviewed after the exam and again at 24 h after the exam. All subjects specifically denied dizziness, nausea, vertigo, headaches, or visual changes. Pure triacylglycerols were obtained from Nu-Chek Prep, Inc. (Elysian, MN). To test the accuracy of the protocol to quantify lipid composition, phantom samples were prepared by mixing tristearin (18:0) (number of carbons:number of double bonds), triolein (18:1), and trilinolein (18:2) in the following ratios: 50:0:50, 50:10:40, 50:20:30, 50:30:20, 50:40:10, 50:50:0, and 25:50:25. Phantom samples with composition of different chain lengths of triglyceride were prepared by mixing tripalmitin (16:0) and tristearin (18:0) in the following ratios: 100:0, 80:20, 75:25, 50:50, 25:75, 20:80 and 0:100. All mixtures were dissolved in CD3Cl in 4 ml glass vials, which were then mounted in the center of a 150 ml beaker filled with deionized water. Typical magnetic resonance spectroscopy (MRS) parameters were: TR 8 s, TE 11 ms, voxel size 0.2 ml, NP 16 k, BW 8 kHz, NA 128. The triglyceride composition was calculated as described below. The 1H chemical shift of in vivo fat resonances from bone marrow and subcutaneous tissue was assigned such that the methyl signal was at 0.9 ppm. Resonance areas were determined by fitting the spectra with Voigt shapes (variable proportions of Lorentzian plus Gaussian) on ACD software (Advanced Chemistry Development, Inc., Toronto, Canada) after phasing and baseline correction. Peak areas for each individual resonance were corrected with its corresponding T1 and T2. Lipid composition was evaluated after correction for relaxation effects. Human adipose tissue is composed largely of triglycerides. Seven fatty acids predominate as follows (number of carbons:number of double bonds, typical abundance): myristic (14:0, 3%), palmitic (16:0, 19–24%), palmitoleic (16:1, 6–7%), stearic (18:0, 3–6%), oleic (18:1, 45–50%), linoleic (18:2, 13–15%), and linolenic (18:3, 1–2%) (22Field C.J. Angel A. Clandinin M.T. Relationship of diet to the fatty acid composition of human adipose tissue structural and stored lipids.Am. J. Clin. Nutr. 1985; 42: 1206-1220Crossref PubMed Scopus (132) Google Scholar, 23Malcom G.T. Bhattacharyya A.K. Velez-Duran M. Guzman M.A. Oalmann M.C. Strong J.P. Fatty acid composition of adipose tissue in humans: differences between subcutaneous sites.Am. J. Clin. Nutr. 1989; 50: 288-291Crossref PubMed Scopus (94) Google Scholar). These fatty acids account for well over 90% of the fatty acids in human adipose tissue. Odd-carbon fatty acids, longer chain fatty acids, and shorter chain fatty acids account for the remainder. Each of these less-abundant fats individually contributes much less than 1% (22Field C.J. Angel A. Clandinin M.T. Relationship of diet to the fatty acid composition of human adipose tissue structural and stored lipids.Am. J. Clin. Nutr. 1985; 42: 1206-1220Crossref PubMed Scopus (132) Google Scholar). At 7 T, 10 resonances can be resolved, designated here as A to J in alphabetic order from upfield to downfield (Fig. 1). Six resonances contribute equivalent information about triglyceride composition: the CH3 methyl protons (labeled A, at ∼0.90 ppm), the CH2 methylene protons α- (E, at ∼2.25 ppm) and β- (C, at ∼1.59 ppm) to the carbonyl, and the glycerol backbone CH (I) and CH2 protons (G and H). Hence, there are only four additional informative resonances to consider: 1) bulk CH2 methylene protons (labeled B at ∼1.3 ppm); 2) allylic CH2 protons, α- to a double bond, at 2.03 ppm (D); 3) diallylic (also called bis-allylic) CH2 protons at 2.77 ppm (F); and 4) olefinic, double bond -CH = CH- protons at 5.31 ppm (J), which partially overlap with the glycerol CH methine proton at 5.21 ppm (I). It was assumed that the fatty acids detected here contain either 0, 1, or 2 double bonds. These three types of fatty acids account for ∼97–98% of total fat in humans on ordinary Western diets. Linolenic acid (18:3) is excluded in this simplification, but it contributes only ∼0.5% of the total triglycerides (22Field C.J. Angel A. Clandinin M.T. Relationship of diet to the fatty acid composition of human adipose tissue structural and stored lipids.Am. J. Clin. Nutr. 1985; 42: 1206-1220Crossref PubMed Scopus (132) Google Scholar). With this assumption, fsat + fmono + fdi = 1 where fsat, fmono, and fdi refer to the fraction of fatty acids that are saturated, monounsaturated, and doubly unsaturated (or diunsaturated), respectively. The fraction that is diunsaturated, fdi, can be determined directly from the relative area of the resonance of the “bridging” diallylic protons (resonance F), with respect to the resonance of methylene protons α to COO (resonance E): fdi=area(F/E)Eq. 1 Once the fdi value is determined, one can evaluate fmono from the relative area of proton resonance α to the double bond by: fmono=0.5*area(D/E)−fdiEq. 2 The remaining unknown fsat, the fraction of saturated fatty acid, is derived as fsat = 1 − (fmono + fdi). Assuming that f16C + f18C = 1, the fraction of fatty acids that are 16 carbon versus 18 carbon can be determined from the area of the bulk methylene resonances (-CH2-)n: Area(B/E)=f16C(12fsat+8fmono)+f18C(14fsat+10fmono+7fdi)Eq. 3 The coefficients in front of the individual fractions are: 12 for palmitic acid (16:0), 8 for palmitoleic acid (16:1), 14 for stearic acid (18:0), 10 for oleic acid (18:1), and 7 for linoleic acid (18:2). This analysis is essentially identical to the earlier analysis (20Strobel K. van den Hoff J. Pietzsch J. Localized proton magnetic resonance spectroscopy of lipids in adipose tissue at high spatial resolution in mice in vivo.J. Lipid Res. 2008; 49: 473-480Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar) with the exception that a term for an unsaturated fat with three double bonds was omitted rather than assuming a low, fixed concentration. 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 chemical shift difference is about 0.1 ppm), the lipid resonances were well-resolved at 7T and qualitatively similar to high-resolution spectra obtained in mice (20Strobel K. van den Hoff J. Pietzsch J. Localized proton magnetic resonance spectroscopy of lipids in adipose tissue at high spatial resolution in mice in vivo.J. Lipid Res. 2008; 49: 473-480Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar). The water signal generally appears in the 1H spectrum of subcutaneous fat tissue, with subject-dependent intensity and line width, but it is nearly undetectable in bone marrow acquired from a small voxel (∼0.1 ml). The resonance assignments, chemical shifts, and relative intensities from both marrow and subcutaneous fat are summarized in Table 1.TABLE 1Chemical shifts and relative resonance areasResonance AreasLetter and StructureChemical GroupChemical ShiftMarrowSubcutaneousppmA (methyl protons)-CH30.90130.2 ± 11.3125.8 ± 14.5B (methylene protons)-(CH2)n-1.30935.0 ± 59.2956.4 ± 73.1C (methylene protons β to COO)-CH2-CH2-COO1.59104.5 ± 12.3109.1 ± 15.4D (methylene protons α to C = C)-CH2-CH = CH-CH2-2.03141.7 ± 10.8146.0 ± 15.2E (methylene protons α to COO)-CH2-COO2.25100100F (diallylic methylene protons)=CH-CH2-CH =2.7724.5 ± 3.123.4 ± 3.9J (methine protons)-CH = CH-5.3162.4 ± 5.763.9 ± 6.2The areas are relative to the methylene resonance α to COO (peak E) after correction for partial saturation. Resonance assignments by letter correspond to Fig. 1. Values are the mean ± 1 SD (n = 20). Open table in a new tab The areas are relative to the methylene resonance α to COO (peak E) after correction for partial saturation. Resonance assignments by letter correspond to Fig. 1. Values are the mean ± 1 SD (n = 20). The validity of this analysis was tested by mixing three C18 triacylglycerols and, in a separate experiment, by mixing C16 and C18 triacylglycerols, in various ratios. Figure 2Ashows data collected from phantoms, with the area (F/E) plotted against the actual known fraction of trilinolein (fdi) in the C18 mixture phantom samples. A linear correlation is seen between the measured F/E ratio and the sample true fdi value, with linear coefficient of 1.02 and correlation coefficient R2 = 0.992. Similar correlations were found for the other components (data not shown). Figure 2B shows the measured C18 triacylglycerol faction (f18C) against the actual known C18 fraction in the C16 and C18 mixture phantom samples. The plot of the known f18C versus the measured f18C, which was evaluated by 0.5 * area (B/E) − 12, also yielded a linear dependence, with linear coefficient of 0.94 and correlation coefficient R2 = 0.992. For quantitation of fat composition in human subcutaneous tissue and tibial marrow, the signal intensities were corrected for all differences in T1 and T2 as determined from inversion-recovery (Fig. 3) and TE-dependent (Fig. 4) experiments, respectively. Figure 3 shows the T1 (left) and T2 (right) spectra collected from the same voxel located in subcutaneous tissue, together with the corresponding curve fittings (bottom). Figure 4 compares the T2 data between tibial marrow and subcutaneous tissue collected from same-sized voxels, on the same volunteer. The measured T1 and T2 values at this field are summarized in Table 2. As shown by the data, protons at different structural positions in fats have quite different values, with T1s ranging from 0.32–1.16 s, and T2s ranging from 30–74 ms. Calf subcutaneous fat has shorter T1 and T2 values, about 7% on average, in comparison with tibial bone marrow. It should be pointed out that because of the presence of proton J-coupling, these T1 and T2 values are valid only for STEAM sequence. Shorter T2 values have been reported for animal abdominal fat using point-resolved spectroscopy (PRESS) sequence (20Strobel K. van den Hoff J. Pietzsch J. Localized proton magnetic resonance spectroscopy of lipids in adipose tissue at high spatial resolution in mice in vivo.J. Lipid Res. 2008; 49: 473-480Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar) at the same field strength.Fig. 4T2 measurement of tibia bone marrow (left panel) and calf subcutaneous fat (right panel) from a 25 year-old healthy female by varying TEs at 7T. Note that the voxel (5 × 5 × 5 mm3) fits well in the single fat cell of the subcutaneous tissue and the collected 1H spectrum is water-free. All spectra are vertically scaled to equal magnitude of the methylene resonance (B), and as a result, with TE increase, the methyl resonance A with longer T2 than B shows signal rising, whereas the shorter T2 resonances such as C and D show signal decaying relative to resonance B. To avoid overcrowding, the fitting of the “A” and “C” peaks is not shown. Other parameters: TR 8 s, number of acquisitions, 8; number of points, 4 k; BW 4 kHz.View Large Image Figure ViewerDownload Hi-res image Download (PPT)TABLE 2Relaxation times in resonances assigned to the fatty acid chain (n = 3–6)T1, Second (n = 3)T2, Milliseconds (n = 6)Chemical GroupMarrowSubcutaneousMarrowSubcutaneous-CH3 (A)1.16 ± 0.041.08 ± 0.0574 ± 667 ± 8-(CH2)n- (B)0.55 ± 0.030.53 ± 0.0469 ± 463 ± 5-CH2-CH2-COO (C)0.39 ± 0.040.32 ± 0.0533 ± 630 ± 6-CH2-CH = CH-CH2- (D)0.42 ± 0.020.39 ± 0.0342 ± 239 ± 3-CH2-COO (E)0.44 ± 0.020.40 ± 0.0260 ± 355 ± 4=CH-CH2-CH = (F)0.60 ± 0.030.58 ± 0.0359 ± 358 ± 3The values shown are mean ± SD and are valid for the stimulated echo acquisition mode pulse sequence used. Open table in a new tab The values shown are mean ± SD and are valid for the stimulated echo acquisition mode pulse sequence used. The derived fractions of saturated, monounsaturated and diunsaturated fat constituents are summarized in Table 3, together with the estimated fraction of fatty acid chain length f16C and f18C. The composition of bone marrow and adipose fat was not significantly different, with an average 29.1 ± 3.5% saturated, 46.4 ± 4.8% monounsaturated, and 24.5 ± 3.1% diunsaturated fractions for marrow, as compared with 27.1 ± 4.2% saturated, 49.6 ± 5.7% monounsaturated, and 23.4 ± 3.9% diunsaturated fractions for subcutaneous fat. A good linear correlation was seen between tibial marrow and subcutaneous fat in the measured area ratio (F/E), which is the index of diunsaturated fraction, for the 20 subjects studied, as shown in Fig. 5. In addition, a composition of 33.4 ± 4.9% from fatty acid with 16 carbons and 66.5 ± 9.7% from fatty acid with 18 carbons was calculated for bone marrow, as compared with subcutaneous fat with a composition of 23.4 ± 3.9% for 16 carbon fraction and 73.8 ± 17.8% for 18 carbon fraction.TABLE 3Average fat composition in marrow and subcutaneous tissuesMarrowSubcutaneousRelative concentration Saturated (fsat)29.1 ± 3.527.1 ± 4.2 Monounsaturated (fmono)46.4 ± 4.849.6 ± 5.7 Diunsaturated (fdi)24.5 ± 3.123.4 ± 3.9Chain length Fraction 16-carbon (f16C)33.5 ± 4.926.2 ± 6.4 Fraction 18-carbon (f18C)66.5 ± 9.773.8 ± 17.9The relative concentration, as percentage of saturated, monounsaturated, and diunsaturated fats, as well as the fraction of 16- vs. 18-carbon fats are shown. Values are the mean ± 1 SD (n = 20). Open table in a new tab The relative concentration, as percentage of saturated, monounsaturated, and diunsaturated fats, as well as the fraction of 16- vs. 18-carbon fats are shown. Values are the mean ± 1 SD (n = 20). High-quality 1H NMR spectra from human adipose tissue were obtained routinely at 7T. The features of the 1H spectra at 7T were consistent with spectra of triacylglycerols obtained under high-resolution conditions (8Zancanaro C. Nano R. Marchioro C. Sbarbati A. Boicelli A. Osculati F. Magnetic resonance spectroscopy investigations of brown adipose tissue and isolated brown adipocytes.J. Lipid Res. 1994; 35: 2191-2199Abstract Full Text PDF PubMed Google Scholar, 9Miyake Y. Yokomizo K. Matsuzaki N. Determination of unsaturated fatty acid composition by high-resolution nuclear magnetic resonance spectroscopy.J. Am. Oil Chem. Soc. 1998; 75: 1091-1094Crossref Google Scholar, 10Guillen M.D. Ruiz A. 1H nuclear magnetic resonance as a fast tool for determining the composition of acyl chains in acylglycerol mixtures.Eur. J. Lipi" @default.
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• W2164183759 date "2008-09-01" @default.
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• W2164183759 title "Composition of adipose tissue and marrow fat in humans by 1H NMR at 7 Tesla" @default.
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