Speaker: June S. Taylor

Title: FAT - It's Not Just Another Image Artifact

Summary: Journal Club today will be devoted to a discussion of the nitty gritty details of using MRS as a biochemical analysis tool - in this case, to assess changes in a metabolic pool of fat (triglyceride) called IntraMyoCellular^? Lipid (IMCL). This fat is in little droplets right next to the mitochondria in skeletal muscle. The fat droplets are small enough that the rotational correlation time is relatively long, long enough that there is partial resolution of the methyl (-CH3) and methylene (-CH2) protons of the fatty acid chains in the triglyceride. I promise to keep the chemistry to a minimum, if y'all will contribute ideas to improve the methodology ( especially in the signal processing).

Title: Distribution of Intramyocellular Lipids in Human Calf Muscles as Determined by MR Spectroscopic Imaging

Authors: Peter Vermathen, Roland Kreis, and Chris Boesch

Abstract: In this study the distribution of intramyocellular lipids (IMCL) in human calf muscles was determined by 1H-MR spectroscopic imaging (MRSI) measurements. An obstacle for MRSI measurements in the calf, including different muscles, is the inevitable inclusion of regions with high concentrations of extramyocellular lipids (EMCL). This can lead to signal bleeding and consequently to unpredictable overlaps of IMCL resonances with EMCL in voxels of interest. The results of this study show that signal bleeding from EMCL can be substantially reduced in voxels from calf muscles by the application of a lipid extrapolation (LE) procedure (Haupt et al., Magn Reson Med 1996;35: 678). The spectra of all voxels located within muscle tissue were .tted, and the metabolite values were assigned to one of 10 different muscles based on image segmentation. Signifcant IMCL differences between some muscles were obtained, with high values in m. soleus and two to three times lower values in the tibialis anterior, tibialis posterior, and gastrocnemius muscles. In addition to gross differences between muscles, significant intersubject differences were observed in both IMCL content and distribution over different muscles. A significant correlation between .ber orientation (obtained from orientation- dependent dipolar coupling of creatine and taurine resonances) and IMCL content was found, indicating that IMCL content is directly correlated to biomechanical properties.

Reference: Magn Reson Med 51:253-262, 2004.

Key words: MR spectroscopic imaging; skeletal muscle; intramyocellular lipids; fiber orientation; lipid extrapolation