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Intramyocellular Lipid Quantification: Repeatability with ¹H MR Spectroscopy¹

¹ From the Division of Musculoskeletal Imaging (M.T., B.J.T., M.E.J., D.I.R., W.E.P.) and Institute for Technology Assessment (E.F.H.), Massachusetts General Hospital and Harvard Medical School, 15 Parkman St, WACC 515, Boston, MA 02114. Received September 27, 2004; revision requested December 2; revision received December 6; accepted January 12, 2005. Supported in part by NIH grant M01 RR01066. Address correspondence to M.T. (e-mail: mtorriani{at}hms.harvard.edu).

PURPOSE: To prospectively determine the repeatability and variability of tibialis anterior intramyocellular lipid (IMCL) quantifications performed by using 1.5-T hydrogen 1 (¹H) magnetic resonance (MR) spectroscopy in healthy subjects.

MATERIALS AND METHODS: Institutional review board approval and written informed consent were obtained for this Health Insurance Portability and Accountability Act–compliant study. The authors examined the anterior tibial muscles of 27 healthy subjects aged 19–48 years (12 men, 15 women; mean age, 25 years) by using single-voxel short-echo-time point-resolved ¹H MR spectroscopy. During a first visit, the subjects underwent ¹H MR spectroscopy before and after being repositioned in the magnet bore, with voxels carefully placed on the basis of osseous landmarks. Measurements were repeated after a mean interval of 12 days. All spectra were fitted by using Java-based MR user interface (jMRUI) and LCModel software, and lipid peaks were scaled to the unsuppressed water peak (at 4.7 ppm) and the total creatine peak (at approximately 3.0 ppm). A one-way random-effects variance components model was used to determine intraday and intervisit coefficients of variation (CVs). A power analysis was performed to determine the detectable percentage change in lipid measurements for two subject sample sizes.

RESULTS: Measurements of the IMCL methylene protons peak at a resonance of 1.3 ppm scaled to the unsuppressed water peak (IMCL_W) that were obtained by using jMRUI software yielded the lowest CVs overall (intraday and intervisit CVs, 13.4% and 14.4%, respectively). The random-effects variance components model revealed that nonbiologic factors (equipment and repositioning) accounted for 50% of the total variability in IMCL quantifications. Power analysis for a sample size of 20 subjects revealed that changes in IMCL_W of greater than 15% could be confidently detected between ¹H MR spectroscopic measurements obtained on different days.

CONCLUSION: ¹H MR spectroscopy is feasible for repeatable quantification of IMCL concentrations in longitudinal studies of muscle metabolism.

© RSNA, 2005

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