Quantitative Characterization of the Corticospinal Tract at 3T

Right-sided corticospinal tracts, reconstructed from DTI data with ROIs chosen as described in “Methods.” Axial sections are portions of color-coded maps derived from FA and the principal eigenvector. In these maps, blue represents tracts running in the rostrocaudal axis; green, anteroposterior; and red, mediolateral; oblique angles are represented by a mixture of colors. The decussation of the superior cerebellar peduncle is denoted by the white arrow at the level of the midbrain in B. 3D representation of the CSTs are superimposed on coregistered magnetization-prepared rapid gradient-echo scans, which are heavily T1-weighted. A, Reconstruction of the right whole-brain CST, with ROIs depicted in green. B, Reconstruction of hemispheric and brain stem portions of the right CST.

MR imaging parameters restricted to the corticospinal tracts of the subject shown in Figs 1 and 2. Left column shows parameter distributions restricted to the CSTs in the whole brain (blue), brain stem (green), and hemispheres (magenta). Each box shows the IQR across the entire reconstructed tract of the parameter labeled on the vertical axis, with the central line representing the median. Middle column shows median MR imaging parameters for the right (black) and left (red) CST, as a function of distance from the lowest section in the medulla. Data are taken from the whole-brain reconstructions. Right column shows IQR versus distance. For this individual, distances <20 mm correspond approximately to the medulla; 20–45 mm, to the pons; 45–60 mm, to the midbrain; 60–85 mm, to the internal capsule; 85–120 mm, to the corona radiata; and >120 mm to the subcortical white matter. For easier visualization, plots in the middle and right columns exclude highly variable data from the lowest and highest sections. Units: ms (T1, T2); 10⁻³ mm²/s (MD, λ₁, λ₂, λ₃, λ_⊥).

Properties of the reconstructed corticospinal tracts. A, Number of reconstructed fibers. B, Tract volume. C and D, Medians (C) and IQRs (D), of individual MR imaging parameters restricted to the CSTs. Black points denote healthy individuals; green, the particular healthy subject of Figs 1–3; and red, an individual with MS. For green and red points, circles denote the right CST, and triangles, the left CST; for black points, the right and left sides are not distinguished. Also shown are means (central horizontal lines) and 99% normal ranges (delimited by flanking horizontal lines) across the population of healthy individuals. Parameter type is given in the vertical axis label for each graph in C; the same labels apply to panel D. Data are randomly scattered along the horizontal axis within each category, for easier visualization. For individuals scanned more than once, cross-scan means are plotted.

Asymmetry indices derived from reconstructed corticospinal tracts. (See the legend to Fig 4 for details on the presentation.) Vertical axis labels in C denote the MR imaging parameters for which asymmetry indices are shown; the same labels apply to panel D.