FIGURE 2.

(A) Diffusion-weighted image. The corticospinal tracts (CSTs) coursing through the posterior limb of the internal capsule (denoted by the arrows) are hyperintense. (B) Diffusion-weighted image with different gradient direction. Note that the CST coursing through the posterior limb of the internal capsule have lost their signal. The diffusion signal goes down if the gradient is applied along the axis of diffusion. Therefore, if the diffusion-encoding gradient is directed superior–inferior, then the CST will decrease in signal intensity on the diffusion-weighted image. Similarly, if the diffusion-encoding gradient is directed anterior–posterior, then the superior longitudinal fasciculus will decrease in signal intensity. Finally, if the diffusion-encoding gradient is directed transversely, then the portions of the corpus callosum will decrease in signal intensity. (C) DTI color-coded fractional anisotropy map. The CSTs running through the posterior limb of the internal capsule are denoted by the blue color, which indicates the tracts are coursing in the superior–inferior direction.