Intramuscular adipose tissue determined by T1-weighted MRI at 3 T primarily reflects extramyocellular lipids

Purpose: The purpose of this study was to assess relationships between intramuscular adipose tissue (IntraMAT) content determined by MRI and intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) determined by H-1 magnetic resonance spectroscopy (H-1 MRS) or echo intensity determined by B-mode ultrasonography of human skeletal muscles. Methods: Thirty young and elderly men and women were included. T1-weighted MRI was taken from the right mid-thigh to measure IntraMAT content of the vastus lateralis (VL) and biceps femoris (BF) using a histogram shape-based thresholding technique. IMCL and EMCL were measured from the VL and BF at the right mid-thigh using H-1 MRS. Ultrasonographic images were taken from the VL and BF of the right mid-thigh to measure echo intensity based on gray-scale level for quantitative analysis. Results: There was a significant correlation between IntraMAT content by MRI and EMCL of the VL and BF (VL, r = 0.506, P < 0.01; BF, r = 0.591, P < 0.001) and between echo intensity and EMCL of the VL and BF (VL, r = 0.485, P < 0.05; BF, r = 0.648, P < 0.01). IntraMAT content was also significantly correlated with echo intensity of the VL and BF (VL, r = 0.404, P < 0.05; BF, r = 0.493, P < 0.01). Conclusion: Our study suggests that IntraMAT content determined by T1-weighted MRI at 3 T primarily reflects extramyocellular lipids, not intramyocellular lipids, in human skeletal muscles. (C) 2015 Elsevier Inc. All rights reserved.