Skeletal muscle lipid concentration quantified by magnetic resonance imaging

Abstract

Background: Skeletal muscle lipid is associated with obesity and type 2 diabetes and may be altered by diet, physical activity, and weight loss. Objective: We explored the utility of magnetic resonance imaging (MRI) for quantifying the lipid concentration of muscle tissue in vivo. Design: Fat-selective MR images of the lower leg were taken in 8 normal-weight [body mass index (in kg/m2) ≤ 24.9] and 8 obese (body mass index > 29.9) subjects to obtain spatial maps of lipid signal intensity within muscle tissue. Fast-spiral-sequence (echo time = 5.6-13.8 ms, repetition time = 1 s, 8 interleaves) MRI scans were conducted at 3.0 T by using an extremity transmit-receive coil. Lipid concentrations within muscle were determined from manually drawn regions of interest in the tibialis anterior (TA), soleus, and medial head of the gastrocnemius (MHG) muscle groups. Results: There was extremely good agreement (mean R2 = 0.985) between the fat signal intensity and the actual lipid concentration of standards containing 2.5, 5.0, and 10.0 g lipid/dL, which were placed on the subject's leg during each scan. The lipid content of both the soleus (2.99 ± 0.37 g/dL) and the MHG (3.80 ± 0.68 g/dL) was higher (P < 0.05) than that of the TA (1.83 ± 0.28 g/dL). Lipid content was more than two-fold higher (P < 0.05) in the MHG of obese subjects (5.48 ± 1.18 g/dL) than in the MHG of normal-weight subjects (2.54 ± 0.47 g/dL), but did not differ significantly in the TA or soleus. Conclusions: MRI can be used to quantify lipid within human muscle tissue. MRI can also be used to detect differences in muscle lipid content among various muscle groups and between normal-weight and obese subjects. © 2004 American Society for Clinical Nutrition.