Muscle Activity during Walking Measured Using 3D MRI Segmentations and FDG-PET

AB Purpose: This study aimed to determine the contribution of each muscle of the lower limb to walking using positron emission tomography (PET) with [18F]-Fluorodeoxyglucose (FDG). Furthermore, we compared our results obtained with volumetric analysis of entire muscles to 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 a total of 90 minutes, 60 minutes before and 30 minutes after intravenous injection of 50 MBq FDG. A PET/CT scan of the lower limb was made subsequently. The three-dimensional contours of 39 muscles in the left lower limb were semi-automatically determined from MRI scans. After non-rigidly registering the MRI to the CT scans we superimposed the muscle contours on the PET scans. Results: The muscles with the highest median FDG uptake over all subjects were the soleus, gluteus maximus, vastus lateralis, gastrocnemius medialis, and adductor magnus. We found a wide range of FDG uptake values between subjects, including in some of the most important muscles involved in walking (e.g. soleus, gluteus medius, gastrocnemius medialis). Compared to 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), and all the thigh muscles (underestimated). Conclusion: 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 3-D image analysis techniques