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