Skeletal muscle lipid concentration quantified by magnetic resonance imaging.

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/m(2)) < or = 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 R(2) = 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.