Muscle Activity during Walking Measured Using 3D MRI Segmentations and [18F]-Fluorodeoxyglucose in Combination with Positron Emission Tomography.

PURPOSE This study aimed to determine the contribution of each muscle of the lower limb to walking using positron emission tomography (PET) with [F]-fluorodeoxyglucose (FDG). Furthermore, we compared our results obtained using volumetric analysis of entire muscles with those obtained using a more traditional approach considering the uptake in only one slice in each segment. METHODS Ten healthy subjects walked on a treadmill at self-selected comfortable walking speed for 90 min, 60 min before and 30 min after intravenous injection of 50-MBq FDG. A PET/computerized tomography scan of the lower limb was made subsequently. The three-dimensional contours of 39 muscles in the left lower limb were semiautomatically determined from magnetic resonance imaging scans. After nonrigidly registering the magnetic resonance imaging to the computerized tomography scans, we superimposed the muscle contours on the PET scans. RESULTS The muscles with the highest median FDG uptake among all subjects were the soleus, gluteus maximus, vastus lateralis, gastrocnemius medialis, and adductor magnus. We found a wide range of FDG uptake values among subjects, including in some of the most important muscles involved in walking (e.g., soleus, gluteus medius, gastrocnemius medialis). Compared with the volumetric analysis, the single slice analysis did not yield an accurate estimate of the FDG uptake in many of the most active muscles, including the gluteus medius and minimus (overestimated) as well as all the thigh muscles (underestimated). CONCLUSIONS The distribution of FDG among the muscles varied between subjects, suggesting that each subject had a unique activation pattern. The FDG uptake as estimated from single slices did not correspond well to the uptake obtained from volumetric analysis, which illustrates the added value of our novel three-dimensional image analysis techniques.