nTMS-based DTI fiber tracking of motor pathways

Abstract

DTI fiber tracking allows for the 3D reconstruction of main white matter fascicles, including the corticospinal tract (CST). Nevertheless, standard diffusion tensor imaging fiber tracking (DTI FT) is limited by the fact that it 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 brain tumor patients, 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. The nTMS technique 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. This improves the reliability and accuracy of the DTI FT of the CST 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. This chapter presents data on the intraoperative correlation of nTMS-based DTI FT of the CST to subcortical direct electrical stimulation and describes the various published protocols of nTMS-based DTI FT of the CST in detail.