Structural properties of the corticospinal tract in the human brain: a magnetic resonance imaging study at 7 Tesla

Several fibre tracts can be accurately located using conventional Magnetic Resonance Images (MRI) of the human brain, including the corticospinal tract (CST), which appears as a T 1 -weighted hypointense/ T 2 -weighted hyperintense patch in the posterior part of the posterior-limb of the internal capsule (PLIC). Here we use high-field MRI (7T) to assess the quantitative MRI properties of the CST at the PLIC level in 22 healthy young male participants. We used three different imaging modalities: the T 1 and T 2 relaxation times ( T 1 and T 2 ) and the Magnetization Transfer Ratio (MTR). These measurements obtained in the CST were compared with those in the anterior two-thirds of the PLIC. We observed longer T 1 and T 2 and lower MTR in the CST region compared with the adjacent (control) PLIC region. This effect is consistent with the presence of sparsely distributed, large-diameter fibres described in previous histological studies and, as such, might reflect lower myelin density and/or different morphology of fibres in the CST.