Spatial Heterogeneity in the Muscle Functional MRI Signal Intensity Time Course: Effect of Exercise Intensity

摘要

It has previously been observed that during isometric dorsiflexion exercise, the time course of T2-weighted signal intensity (SI) changes is spatially heterogeneous. The purpose of this study was to test the hypothesis that this spatially heterogeneity would increase at higher contraction intensities. Eight subjects performed 90s isometric dorsiflexion contractions at 30 and 60% of maximum voluntary contraction (MVC) while T2-weighted (TR/TE=4000/35ms) images were acquired. SI was measured before, during, and after the contractions in regions of interest (ROIs) in the extensor digitorium longus (EDL) muscle and the deep and superficial compartments of the tibialis anterior (D-TA and S-TA, respectively). For all ROIs at 30% MVC, SI changes were similar. The maximum post-contraction SI was greater than the SI during exercise. At 60% MVC, SI changes during contraction were greater in the S-TA than in the DTA and EDL. For the EDL and D-TA, the maximum post-contraction SI was greater than those during exercise. For the S-TA, the maximum post-contraction change was greater than the changes at t=8, 20, and 56 s, but not the end-exercise value. We conclude that spatial heterogeneity increases during more intense dorsiflexion contractions, possibly reflecting regional differences in perfusion or neural activation of the muscle.