Archer, Patten, Coombes - 2017 - Free-water and free-water corrected fractional anisotropy in primary and premotor corticospinal tracts.pdf

Measures from diffusion MRI have been used to characterize the corticospinal tract in<br>chronic stroke. However, diffusivity can be influenced by partial volume effects from free-water,<br>region of interest placement, and lesion masking. We collected diffusion MRI from a cohort of chronic<br>stroke patients and controls and used a bitensor model to calculate free-water corrected fractional<br>anisotropy (FAT) and free water (FW) in the primary motor corticospinal tract (M1-CST) and the dorsal<br>premotor corticospinal tract (PMd-CST). Region of interest analyses and whole-tract slice-by-slice analyses<br>were used to assess between-group differences in FAT and FW in each tract. Correlations between<br>FAT and FW and grip strength were also examined. Following lesion masking and correction for multiple<br>comparisons, relative increases in FW were found for the stroke group in large portions of the M1-<br>CST and PMd-CST in the lesioned hemisphere. FW in cortical regions was the strongest predictor of<br>grip strength in the stroke group. Our findings also demonstrated that FAT is sensitive to the direct<br>effects of the lesion itself, thus after controlling for the lesion, differences in FAT in nonlesioned tissue<br>were small and generally similar between hemispheres and groups. Our observations suggest that FW<br>may be a robust biological measurement that can be used to assess microstructure in residual white<br>matter after stroke.