Symmetry and spatial distribution of muscle glucose uptake in the lower limbs during walking measured using FDG-PET

Abstract

Purpose This study aimed to elucidate whether muscle activity (in terms of glucose uptake) between the legs can be considered symmetrical during walking. Furthermore, we aimed to determine whether the [ 18 F]-fluorodeoxyglucose was distributed heterogeneously throughout each muscle, and if so, whether areas of high uptake would be clustered. Methods Ten healthy participants 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 [ 18 F]-fluorodeoxyglucose. Thereafter, a positron emission tomography/computed tomography scan of the lower limb was acquired. Three-dimensional muscle contours of 78 (= 39x2) muscles of the left and right lower limb were semi-automatically determined from magnetic resonance imaging scans. After non-rigid registration, those muscle contours were used to extract [ 18 F]-fluorodeoxyglucose uptake from the positron emission tomography scans. Results Large asymmetries were observed in the lower leg muscles (e.g. median absolute asymmetry index of 42% in the gastrocnemius medialis) and in the gluteus minimus (30% asymmetry) and gluteus medius (15% asymmetry), whereas the uptake in the thighs was relatively symmetrical between the limbs (<6% asymmetry). These were not related to limb-dominance nor to inter-limb differences in muscle volume. The [ 18 F]-fluorodeoxyglucose distribution was not distributed normally; most voxels had a relatively low standardized uptake value, and a minority of voxels had a relatively high standardized uptake value. The voxels with higher [ 18 F]-fluorodeoxyglucose uptake were distributed heterogeneously; they were clustered in virtually all muscles. Conclusion The findings in this study challenge the common assumption of symmetry in muscle activity between the limbs in healthy subjects. The clustering of voxels with high uptake suggests that even in this prolonged repetitive task, different spatial regions of muscles contribute differently to walking than others.

A three-dimensional finite-element model of gluteus medius muscle incorporating inverse-dynamics-based optimization for simulation of non-uniform muscle contraction

“…It was found that contraction in GM is highly non-uniform across its subdivisions during different motions. This is generally in agreement with previous EMG and FDG-PET studies [8,[11][12][13][14]. There was also a marked difference in the biomechanics of GM between the models with and without the consideration of non-uniform contraction.…”

“…There are a number of studies on non-uniform muscle contraction, mostly using electromyography (EMG) [8,[11][12][13] or FDG-PET (monitor fluorodeoxyglucose (FDG) uptake through positron emission tomography (PET)) [14]. However, the reliability of using EMG as an approach to measure biomechanics of muscles is questionable due to uncertainties in the acquisition and conversion of EMG signals into biomechanical response of muscles.…”

Radiopharmaceuticals for Skeletal Muscle PET Imaging

“…[ 18 F]FDG PET can clearly identify the entire muscleactivated region (Figure 1). Utilizing PET advantages, several studies have successfully identified activated muscle areas during various exercises such as pinching, skiing, and pedaling [28][29][30][31][32]41].…”

Statistical parametric mapping of three-dimensional local activity distribution of skeletal muscle using magnetic resonance imaging (MRI)

“…Two-dimensional (2D) muscular activity distributions have been reported using surface electrodes allocated in an array 12 – 14 ; however, to the best of our knowledge, there are no reports of 3D activity distributions that include deep muscle. Although the 3D distribution of glucose metabolism in muscles could be evaluated by fluorodeoxyglucose-positron emission tomography (FDG-PET) 15 , whole-body radiation exposure is a concern.…”

“…Despite limited information regarding its mechanism, T2 was reported to demonstrate a high correlation with glucose uptake within the muscle in both whole muscle and per-pixel analyses 22 , and by analyzing T2 shifts before and after exercise per voxel units, analysis of local activity distributions within muscles has been reported 23 . However, as there are significant individual differences in muscle form and their internal structures 24 , and the 3-dimensional activation patterns of skeletal muscle differ significantly between subjects even when performing the same motor task 15 , there was no method of analyzing trends in local activity distribution common to multiple subjects. On the contrary, in the analysis of brain MRI, morphological standardization called “spatial normalization” has been performed by nonlinear registration of brain images in many subjects with a template image of a standard brain form, and then the common regions of signal intensity change within the subject group have been detected by statistical parametric mapping (SPM) 25 – 27 .…”