Investigation of muscle lipid metabolism by localized one‐ and two‐dimensional MRS techniques using a clinical 3T MRI/MRS scanner

Abstract

Purpose:To demonstrate the feasibility of estimating the relative intra-and extramyocellular lipid (IMCL and EMCL) pool magnitudes and calculating the degree of lipid unsaturation within soleus muscle using single-voxel localized oneand two-dimensional (1D and 2D) MR spectroscopy (MRS). Materials and Methods:Localized 1D point resolved spectroscopy (PRESS) and 2D correlation spectroscopy (L-COSY) were performed in identical locations in the soleus muscle of 10 healthy subjects. A GE 3-T MRI/MRS scanner and a quadrature extremity transmit/receive coil was used. Results:The 1D and 2D MR spectra were used to compute IMCL/creatine (Cr) and EMCL/Cr ratios. In addition to cross peaks between the methyl and methylene protons in the high-field region, the 2D spectra showed cross peaks due to J-coupling between allylic, diallylic methylene protons, and olefinic protons. The cross-peak volume ratios also provided a measure of double bonds, suggesting that this ratio can be used to assess unsaturation within IMCL and EMCL lipid pools. Conclusion:We have demonstrated the feasibility of detecting 2D cross peaks between different groups of IMCL and EMCL, including the unsaturated protons within these two lipids pools. This protocol may be easily extended to study the lipids present in other tissues.

Distinct patterns of fat metabolism in skeletal muscle of normal-weight, overweight, and obese humans

“…The radiofrequency pulse bandwidths and details of the sequence were as described in our previous work (36); acquisition parameters included TR/TE of 2 s/24 ms, 64 excitations, acquisition of 2,048 complex points, and spectral width of 5 kHz.…”

“…Localized 2-D correlation spectroscopy (35)(36), in which cross peaks are formed from indirect spin-spin couplings, was performed on all subjects with a minimal TE of 30 ms and 64 incremented time steps (t 1), with increment (⌬t1) ϭ 0.8 ms, resulting in a spectral bandwidth of 1,250 Hz along the second, indirectly detected, spectral dimension. The signals for each value of t 1 were averaged over eight scans, resulting in a total acquisition time of ϳ17 min.…”

“…All data sets were linear predicted from 50 t 1 points to 100 t1 points along the F1 dimension and zero filled to 256 points. The diagonal and cross peaks were assigned, and the volume integrals were quantified, including corrections for T 1 relaxation as described previously (36). The diagonal peak volumes from (CH 2)n protons within the IMCL (1.2, 1.2 ppm) and EMCL (1.35, 1.35 ppm) and the creatine (Cr) signal at 3.03 ppm were estimated.…”

“…Therefore, the goal of this work is to elucidate the relationship between BMI, IMCL, and EMCL and the degree of unsaturation as determined by noninvasive MRS studies. The MRS analysis was performed using our recently introduced methods for improved quantification of the IMCL and EMCL pools and their degree of unsaturation (36,37). These techniques separate the overlapping resonances of IMCL and EMCL and the saturated and unsaturated pools within them by means of two-dimensional (2-D) spectroscopy (36,37), as opposed to the one-dimensional (1-D) spectroscopic approach applied by previous investigators (2).…”

“…The MRS analysis was performed using our recently introduced methods for improved quantification of the IMCL and EMCL pools and their degree of unsaturation (36,37). These techniques separate the overlapping resonances of IMCL and EMCL and the saturated and unsaturated pools within them by means of two-dimensional (2-D) spectroscopy (36,37), as opposed to the one-dimensional (1-D) spectroscopic approach applied by previous investigators (2). Although this previous work permitted correlation of the combined saturated and unsaturated components of IMCL and EMCL to pathology, our approach, leading to individual quantification of the saturated and unsaturated fatty acids within these pools, permits a substantially more detailed characterization of lipid status.…”