Regional homogeneity analysis of resting-state muscle fMRI for detection of contraction-related activity: a pilot...

Assessing muscle activity is essential for diagnosis and treatment of movement disorders such as dystonia and spasticity. While task-based muscle functional magnetic resonance imaging (m-fMRI) 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 resting-state muscle fMRI (rs-m-fMRI) approach based on regional homogeneity (ReHo) to evaluate muscle activity from spontaneous BOLD fluctuations during sustained isometric contraction without block-design contrasts. Eight healthy male participants performed separate isometric plantar and dorsal foot flexion tasks during 3 T MRI scanning. rs-m-fMRI data were analyzed using ReHo to assess local synchronization of BOLD signal. Calf muscle activation was quantified as the percentage of suprathreshold z-transformed ReHo voxels within each segmented muscle and activation thresholds were derived via ROC analysis. ROC analysis demonstrated moderate discrimination between expected active and inactive muscle regions (AUC = 0.63), with sensitivity of 0.57 and specificity of 0.61 at the selected threshold. Consistent condition-related differences were observed between active and inactive muscles during both conditions, with a higher percentage of suprathreshold zReHo voxels in voluntarily contracted muscles. This pilot study demonstrates the feasibility of detecting contraction-related ReHo differences using rs-m-fMRI from a single continuous acquisition. The activation threshold was internally calibrated using expected agonist and antagonist muscle groups and therefore does not represent an externally validated classifier. Further studies incorporating independent physiological validation, reproducibility assessment and larger patient cohorts are required before clinical translation.