Technical evaluation of in vivo abdominal fat and IMCL quantification using MRI and MRSI at 3 T

ObjectivesThe objectives of this study were to develop protocols that measure abdominal fat and calf muscle lipids with magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS), respectively, at 3 T and to examine the correlation between these parameters and insulin sensitivity.Materials and MethodsTen nondiabetic subjects [five insulin-sensitive (IS) subjects and five insulin-resistant (IR) subjects] were scanned at 3 T. Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) were segmented semiautomatically from abdominal imaging. Intramyocellular lipids (IMCL) in calf muscles were quantified with single-voxel MRS in both soleus and tibialis anterior muscles and with magnetic resonance spectroscopic imaging (MRSI).ResultsThe average coefficient of variation (CV) of VAT/(VAT+SAT) was 5.2%. The interoperator CV was 1.1% and 5.3% for SAT and VAT estimates, respectively. The CV of IMCL was 13.7% in soleus, 11.9% in tibialis anterior and 2.9% with MRSI. IMCL based on MRSI (3.8±1.2%) were significantly inversely correlated with glucose disposal rate, as measured by a hyperinsulinemic–euglycemic clamp. VAT volume correlated significantly with IMCL. IMCL based on MRSI for IR subjects was significantly greater than that for IS subjects (4.5±0.9% vs. 2.8±0.5%, P=.02).ConclusionMRI and MRS techniques provide a robust noninvasive measurement of abdominal fat and muscle IMCL, which are correlated with insulin action in humans.