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

Abstract 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 by1 H magnetic resonance spectroscopy (1 H 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 using1 H 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.