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FIG 3. Representation of the method used to identify the CST. Two regions of interest that contained the CST were selected: the motor homunculus of the precentral gyrus (yellow) and the posterior limb of the internal capsule (orange).
A, Using a lower FA, diffusion trace images of the precentral gyrus (yellow) would show all the white matter tracts emanating from the motor cortex. These would include tracts to the posterior limb of the internal capsule, the corpus callosum, and multiple other areas in the frontal and parietal lobes (red lines).
B, Similarly, diffusion trace images of the posterior limb of the internal capsule (orange) would show the CST and multiple other white matter tracts to the frontal and parietal lobes (red lines). To eliminate the white matter tracts that were depicted in each tracing but were not part of the CST, we mathematically intersected the two maps, eliminating those tracings that were not present on both maps.
C, Resultant map showed only the CST that was common to maps A and B.
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