Regional Homogeneity in Muscle Resting-State fMRI as a Novel Marker of Muscle Activation

Assessing muscle activity is essential for diagnosis and treatment of neuromuscular disorders such as spasticity and dystonia. While muscle functional magnetic resonance imaging (MRI) enables non-invasive imaging of muscle activation, conventional methods rely on comparisons between rest and activity, which are unsuitable for patients with sustained muscle contractions. This pilot study introduces a novel resting-state fMRI (rs-fMRI) approach using regional homogeneity (ReHo) to evaluate muscle activity without requiring activation paradigms. Eight healthy male participants performed separate isometric plantar and dorsal foot flexion tasks during 3T MRI scanning. rs-fMRI data were analyzed using ReHo to assess local synchronization of BOLD signal. Calf muscle activation was quantified using z-transformed ReHo values and activation thresholds were derived via ROC analysis. Statistical differences in activation between tasks were assessed using the Wilcoxon signed-rank test. Significant ReHo differences were observed between active and inactive muscles during both tasks. This study demonstrates the potential of rs-fMRI combined with ReHo analysis as a non-invasive method for detecting muscle activity using one series of volumes. Further research in larger cohorts is warranted to validate and expand this approach.