nTMS-Based DTI Fiber Tracking of Motor Pathways

Diffusion tensor imaging (DTI) fiber tracking (FT) allows for a tridimensional reconstruction of main white matter fascicles, including the corticospinal tract (CST). Nevertheless, standard DTI FT is limited by the fact that is based on the selection of anatomical landmarks as seeding regions of interest (ROIs) for tract computation. This reduces the reliability and reproducibility of DTI FT results, especially in patients with brain tumors, in which the neural plasticity induced by the tumor itself causes a reorganization of the motor network resulting in a mismatch between anatomical and functional landmarks. Navigated transcranial magnetic stimulation (nTMS) provides a reliable mapping of the functional organization of the motor cortex that can be successfully used as seeding ROI for the DTI computation of the CST, improving the reliability and accuracy of the DTI FT of the CST as compared to the standard DTI technique. Moreover, it provides the somatotopic organization of the CST, especially improving the visualization of fiber bundles connected to the motor cortical representation of arm and face muscles.