twenty healthy adults ( twelve females and eight males ) age 2252 years ( average 34 years ; without diabetes or known vascular disease ) were studied supine or prone in a 7 t 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 mm ( 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 h 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 . ( 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 h 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 . , seven fatty acids predominate as follows ( number of carbons : number of double bonds , typical abundance ) : myristic ( 14:0 , 3% ) , palmitic ( 16:0 , 1924% ) , palmitoleic ( 16:1 , 67% ) , stearic ( 18:0 , 36% ) , oleic ( 18:1 , 4550% ) , linoleic ( 18:2 , 1315% ) , and linolenic ( 18:3 , 12% ) ( 22 , 23 ) . 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% ( 22 ) . at 7 t , 10 resonances can be resolved , designated here as a to j in alphabetic order from upfield to downfield ( fig . six resonances contribute equivalent information about triglyceride composition : the ch3 methyl protons ( labeled a , at 0.90 ppm ) , the ch2 methylene protons - ( e , at 2.25 ppm ) and - ( 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 , - 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 ) . h nmr spectra of subcutaneous fat ( left ) and tibial bone marrow ( right ) from a 26 year - old healthy male at 7 tesla ( 7 t ) . the bottom trace shows the acquired spectrum , and the upper trace shows the fitted spectrum . a water signal is seen in the spectrum of subcutaneous fat but not bone marrow . a t2-weighted image shows the position of the voxel in the subcutaneous fat tissue and tibial bone marrow ( 5  5  5 mm ) from which the spectra were acquired . 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 9798% 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 ( 22 ) . 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  to coo ( resonance e):eq . 1\documentclass[10pt]{article } 
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 \begin{equation*}{\mathrm{f}}_{{\mathrm{di}}}\;=\;{\mathrm{area}}\;({\mathrm{f / e}})\end{equation*}\end{document } once the fdi value is determined , one can evaluate fmono from the relative area of proton resonance  to the double bond by : eq . 2\documentclass[10pt]{article } 
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 \begin{equation*}{\mathrm{f}}_{{\mathrm{mono}}}\;=\;0.5*{\mathrm{area}}\;({\mathrm{d / e}})\;-\;{\mathrm{f}}_{{\mathrm{di}}}\end{equation*}\end{document } 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 : eq . 3\documentclass[10pt]{article } 
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 \begin{equation*}{\mathrm{area}}\;({\mathrm{b / e}})\;=\;{\mathrm{f}}_{{\mathrm{16c}}}(12{\mathrm{f}}_{{\mathrm{sat}}}\;+\;8{\mathrm{f}}_{{\mathrm{mono}}})\;+\;{\mathrm{f}}_{{\mathrm{18c}}}(14{\mathrm{f}}_{{\mathrm{sat}}}\;+\;10{\mathrm{f}}_{{\mathrm{mono}}}\;+\;7{\mathrm{f}}_{{\mathrm{di}}})\end{equation*}\end{document } 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 ( 20 ) with the exception that a term for an unsaturated fat with three double bonds was omitted rather than assuming a low , fixed concentration . twenty healthy adults ( twelve females and eight males ) age 2252 years ( average 34 years ; without diabetes or known vascular disease ) were studied supine or prone in a 7 t 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 mm ( 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 h 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 . ( 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 h 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 . , 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 , 1924% ) , palmitoleic ( 16:1 , 67% ) , stearic ( 18:0 , 36% ) , oleic ( 18:1 , 4550% ) , linoleic ( 18:2 , 1315% ) , and linolenic ( 18:3 , 12% ) ( 22 , 23 ) . 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% ( 22 ) . 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 - ( e , at 2.25 ppm ) and - ( 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 , - 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 ) . h nmr spectra of subcutaneous fat ( left ) and tibial bone marrow ( right ) from a 26 year - old healthy male at 7 tesla ( 7 t ) . the bottom trace shows the acquired spectrum , and the upper trace shows the fitted spectrum . a water signal is seen in the spectrum of subcutaneous fat but not bone marrow . a t2-weighted image shows the position of the voxel in the subcutaneous fat tissue and tibial bone marrow ( 5  5  5 mm ) from which the spectra were acquired . 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 9798% 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 ( 22 ) . 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  to coo ( resonance e):eq . 1\documentclass[10pt]{article } 
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 \begin{equation*}{\mathrm{f}}_{{\mathrm{di}}}\;=\;{\mathrm{area}}\;({\mathrm{f / e}})\end{equation*}\end{document } once the fdi value is determined , one can evaluate fmono from the relative area of proton resonance  to the double bond by : eq . 2\documentclass[10pt]{article } 
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 \begin{equation*}{\mathrm{f}}_{{\mathrm{mono}}}\;=\;0.5*{\mathrm{area}}\;({\mathrm{d / e}})\;-\;{\mathrm{f}}_{{\mathrm{di}}}\end{equation*}\end{document } 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 : eq . 3\documentclass[10pt]{article } 
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 \begin{equation*}{\mathrm{area}}\;({\mathrm{b / e}})\;=\;{\mathrm{f}}_{{\mathrm{16c}}}(12{\mathrm{f}}_{{\mathrm{sat}}}\;+\;8{\mathrm{f}}_{{\mathrm{mono}}})\;+\;{\mathrm{f}}_{{\mathrm{18c}}}(14{\mathrm{f}}_{{\mathrm{sat}}}\;+\;10{\mathrm{f}}_{{\mathrm{mono}}}\;+\;7{\mathrm{f}}_{{\mathrm{di}}})\end{equation*}\end{document } 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 ( 20 ) 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 7 t h 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 7 t and qualitatively similar to high - resolution spectra obtained in mice ( 20 ) . the water signal generally appears in the h 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 . chemical shifts and relative resonance areas the areas are relative to the methylene resonance  to coo ( peak e ) after correction for partial saturation . 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 2a shows 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 r = 0.992 . 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 r = 0.992 . a : correlation of the known , prepared fraction of diunsaturated triglyceride with mr - measured fraction of diunsaturated triglyceride . phantoms were prepared by mixing three c18 triglycerides ( number of double bonds ) , tristearin ( 0 ) , triolein ( 1 ) , and trilinolein ( 2 ) in the following ratios ( tristearin : triolein : trilinolein ) : 50:0:50 , 50:10:40 , 50:20:30 , 50:30:20 , 50:40:10 , 50:50:0 , and 25:50:25 . b : correlation of the known , prepared fraction of c18 triglyceride with mr - measured value from area ( b / e ) . phantoms were prepared by mixing c16 tripalmitin and c18 tristearin with the following ratios ( c16:c18 ) : 100:0 , 80:20 , 75:25 , 50:50 , 25:75 , 20:80 , and 0:100 . the data were analyzed using f18c = 0.5 * area ( b / e )  12 . 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 . 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 0.321.16 s , and t2s ranging from 3074 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 ( 20 ) at the same field strength . inversion - recovery measurement of t1 ( left panel ) and echo time ( te)-dependence measurement of t2 ( right panel ) from subcutaneous fat tissues of a 34 year - old healthy male at 7 t . the inversion bandwidth ( bw ) was set to span resonances a and b ( middle stack ) , or resonances c , d , e , and f ( left - most stack ) . the inversion delay times for the given spectra are 10 , 20 , 50 , 100 , 200 , 500 , 1,000 , 2,000 , and 3,000 ms with a constant repetition time ( tr ) of 7 s and te of 40 ms ( left panel ) . the echo times for the t2 measurements are 20 , 40 , 60 , 80 , 100 , 140 , and 180 ms ( right panel ) . t2 measurement of tibia bone marrow ( left panel ) and calf subcutaneous fat ( right panel ) from a 25 year - old healthy female by varying tes at 7 t . note that the voxel ( 5  5  5 mm ) fits well in the single fat cell of the subcutaneous tissue and the collected h 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 . n = 36 ) 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 . , 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 . average fat composition in marrow and subcutaneous tissues the relative concentration , as percentage of saturated , monounsaturated , and diunsaturated fats , as well as the fraction of 16- vs. 18-carbon fats are shown . correlation of measured area ( f / e ) between tibial bone marrow and subcutaneous fat for the 20 healthy adult subjects studied , showing that the diunsaturated fatty acid is similar for these two adipose sites and that the fat composition variation among subjects is detectable by h magnetic resonance spectroscopy . high - quality h nmr spectra from human adipose tissue were obtained routinely at 7 t . the features of the h spectra at 7 t were consistent with spectra of triacylglycerols obtained under high - resolution conditions ( 812 ) or in mice at 7 t ( 20 ) . perhaps the most significant observation was that chemical shift dispersion in humans is greatly improved compared with 1.5 t or 3.0 t. the ability to resolve protons adjacent to double bonds allows noninvasive estimation of the fatty acid composition of adipose tissue . proton - decoupled c nmr of human adipose tissue ( 1519 ) allows more - detailed characterization of fat composition , compared with a h spectrum . for example , the outer unsaturated carbons in a bisallylic group ( -ch2-ch = ch - ch2-ch = ch - ch2- ) are resolved from the inner carbons in spectra obtained in vivo at 1.5 t. natural abundance c nmr is limited by relatively low sensitivity , low spatial resolution and additional technical requirements , all disadvantages compared with h spectroscopy for human study . conversely , 7 t instruments are not widely available . however , because the number of 7 t instruments in medical sites is increasing steadily and h spectroscopy is routine on all systems , it seems reasonable to anticipate use of h spectroscopy at 7 t for clinical research . at 7 t the three resonances in the narrow range of 2.032.77 ppm provide an internal standard plus information about the abundance of protons between or adjacent to double bonds . this information , after correction for relaxation , allows calculation of the relative concentration of saturated , monounsaturated , and diunsaturated fatty acids . the fraction of saturated fats in triglycerides as determined by h nmr spectroscopy at 7 t , about 2729% , is in excellent agreement with literature values . however , the fraction of fatty acids that are monounsaturated was somewhat less ( about 4650% ) in this study , compared with biopsy studies , where about 5560% monounsaturated fatty acids are typically found ( 22 , 24 ) . consequently , the fraction of fatty acids estimated to be diunsaturated was about 2324% in this study compared with about 1718% in biopsy studies . first , macromolecules or aqueous metabolites with chemical shifts overlapping the lipid resonances may alter the estimates of relative intensity . second , the signals in vivo are the sum of very complex h spin - coupled multiplets from several different fatty acids with slightly different chemical shifts . consequently , a single lorentzian - gaussian line does not properly represent the observed lineshape . even when high - resolution analytical h nmr was used to measure marrow fat composition from samples extracted in chloroform , thereby removing aqueous species and other complicating factors that may contribute error in the study of intact tissue , the nmr method overestimated the fraction of saturated fatty acids , compared with  gold standard third , as emphasized earlier ( 20 ) , correction for t2 is also essential and more important than correction for t1 differences . for a typical te of 11 ms , the relative difference in t2 correction among the resonances d , e , and f accounts for 4% , but it reaches 8% at te = 20 ms , and is as large as 18% at te = 40 ms . this compares to only about 1% difference after correction for t1 effects for the same three resonances at tr = 2 s. the t1 correction is not needed when the spectrum is collected with tr of 4 s. it is found that the calf subcutaneous fat has relatively shorter ( 7% ) proton relaxation times than the marrow ( table 2 ) , indicating a larger local bo field inhomogeneity on subcutaneous tissue . this can be understood from the difference in the microscopic structure between these two types of adipose tissues , as shown in the mri images ( fig . 4 , insert ) , in which subcutaneous tissue is seen as packed with large fat cells of different sizes , embedded with rich vasculature , and curvedly shaped , whereas the bone marrow appears as fine uniform structure , aligned straight inside the tibial bone , and nearly parallel to the bo field . because of this , the spectral resolution from bone marrow is generally superior to that from subcutaneous fat , as shown in fig . it is probably unrealistic to anticipate perfect correlation between this mr analysis of extremity fat and marrow compared with literature data obtained largely from the abdomen , chest , or buttocks . there are complex effects of diet , season , gender , and anatomical site on fatty acid composition ( 24 , 25 ) . for example , extremity adipose tissue has a greater fraction of monounsaturated fat and less saturated fat compared with subcutaneous fat from the chest and abdomen ( 25 ) . nevertheless , the average ratio fdi / fmono ( 47% for subcutaneous fat and 53% for bone marrow , table 3 ) obtained from this h mrs study for 20 adult subjects ( average age 34 ) , is in excellent agreement with a previously reported value ( 50% ) for the ratio of polyunsaturated to monounsaturated fatty acid by in vivo c study ( 19 ) of calf subcutaneous tissue of 17 adult subjects ( average age 30 ) . the obvious advantage of h mrs is that it is fast ( less than 1 min ) , has a low specific absorption rate ( no need for broadband decoupling as in c ) , is easily localized ( not a volume detection ) , and is typically more easily implemented ( no special scanner hardware or coil required ) . the high resolution and sensitivity of the current steam - based h mr analysis also enable the detection of fat composition variation among uncontrolled healthy subjects ( fig . 5 ) , which might be attributed to the difference in individuals long - term diet and metabolic genetics . therefore , it is anticipated that the method may be useful in rapid detection of substantial changes in the composition of fatty acids in response to diet , exercise , and fat - metabolic diseases . this method , in our view , would help advance noninvasive human lipid research , which has been focused on studying fat mass distribution by mri and other techniques rather than fat molecular structural composition . in addition , an analysis of our data ( not shown ) indicates no obvious difference in fat composition between male and female subjects , although , on average , the calf subcutaneous fat in female is approximately two - fold thicker than in male . the decision to simplify the description of fatty acid composition to saturated , monounsaturated , and diunsaturated fats was based on two considerations . first , the amount of polyunsaturated fats ( three or more double bonds ) in human adipose tissue contributes very little , less than 12% , to the total h nmr signal . second , earlier studies that were able to quantify triply unsaturated fatty acids separate from other fatty acids required high - resolution analytical conditions ( 1012 ) . for practical purposes in humans , this achievement would mean the capacity to separately quantify oleic ( 18:1 ) , linoleic ( 18:2 ) , and linolenic ( 18:3 ) acid . however , at the resolution achieved in these studies , a 50:50 mixture of triolein : trilinolenin is indistinguishable from a spectrum of trilinolein . for these reasons , the description of fatty acids as saturated , monounsaturated , or diunsaturated seems a reasonable simplification . frequency - dependent spatial localization introduces a chemical shift displacement artifact in the h mr spectrum . quantitation may be inaccurate if it is based on ratios of two resonances when the region of interest is close to the inter - tissue boundary . although this effect was not critically evaluated in this study , the use of a small voxel ( 0.1 ml ) well within the bone marrow plus analysis of resonances over a narrow chemical shift range reduces susceptibility to chemical shift displacement effects . unlike the methyl resonance , the resonance of protons  to the carbonyl is not affected by the neighboring large bulk ch2 ( resonance b ) , which often induces an uneven baseline at nearby resonances at shorter tes . although this baseline problem can be improved at longer tes , the faster decay of protons  to a double bond ( resonance d , t2 = 42 ms for marrow , and 39 for subcutaneous fat ) than the reference resonance e ( t2 = 59 ms ) makes long te scan conditions less favorable . steam sequence has the advantage of shorter te than press and less dependence on proton j modulation due to the smaller te / t2 ratio , and therefore was chosen for the quantification of fat composition in this method . in addition to composition analysis , the well - resolved resonances of human tibial bone marrow and calf subcutaneous fat at 7 t could also be very useful as an internal standard to quantify intramuscular lipids ( 26 ) , which have attracted great research interest over the last few years , owing to their relation to insulin sensitivity , diabetes , and obesity ( 27 ) . in conclusion , this h mrs study at 7 t indicates that the rapid acquisition of high - quality h nmr spectra from subcutaneous fat and from bone marrow is straightforward in healthy volunteers , and that the spectra may be analyzed to assess triglyceride composition . this may facilitate longitudinal monitoring of changes in lipid composition in response to diet , exercise , and disease .
proton nmr spectroscopy at 7 tesla ( 7 t ) 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 7 t 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 .