title: Orientation of lipid strands in the extracellular compartment of muscle: effect on quantitation of intramyocellular lipids.
abstract: Single-voxel (1)H NMR spectra from gastrocnemius and soleus muscle were acquired in healthy volunteers at 7T with the objective of measuring the concentration of intramyocellular lipid [IMCL] (note: throughout this article, square brackets indicate concentration). However, significant asymmetry in the resonance assigned to the methylene protons (-CH(2)-)(n) in extramyocellular lipids (EMCL) interfered with fitting the spectra. Since muscle fibers in these tissues are generally not parallel to B(0), the influence of variable orientation in strands of extracellular fat was examined using a mathematical model. Modest variation in orientation produced asymmetric lineshapes that were qualitatively similar to typical observations at 7T. Analysis of simulated spectra by fitting with a Voigt function overestimated [IMCL]/[EMCL] except when EMCL fibers were nearly parallel to B(0). Estimates of [IMCL]/[EMCL] were improved by including variations in fiber orientation in the lineshape analysis (fiber orientation modeling, or FOM). Calculated [IMCL] using FOM, 4.8 +/- 2.2 mmol/kg wet weight, was lower compared to most previous reports in soleus.
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8568, USA.
authors.forename: Anthony
authors.initials: A
authors.lastname: Khuu
authors.forename: Jimin
authors.initials: J
authors.lastname: Ren
authors.forename: Ivan
authors.initials: I
authors.lastname: Dimitrov
authors.forename: Donald
authors.initials: D
authors.lastname: Woessner
authors.forename: James
authors.initials: J
authors.lastname: Murdoch
authors.forename: A Dean
authors.initials: AD
authors.lastname: Sherry
authors.forename: Craig R
authors.initials: CR
authors.lastname: Malloy
mesh_terms: D000328:Adult; D000368:Aged; D045604:Extracellular Fluid / Q000737:chemistry / Q000378:metabolism; D005260:Female; D006801:Humans; D008055:Lipids / Q000032:analysis* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000378:metabolism*; D011522:Protons; D055815:Young Adult
chemical_list: D008055:Lipids; D011522:Protons