Microscopic fractional anisotropy with free water elimination

Water diffusion anisotropy is a diffusion MRI metric that is sensitive to brain injury and neurodegeneration. Microscopic fractional anisotropy (μFA) is a new metric of diffusion anisotropy that is immune to crossing fiber effects, unlike traditional FA, which enables probing of axon integrity in gray matter and crossing white matter tracts. However, μFA is underestimated in voxels adjacent to cerebrospinal fluid (CSF) due to partial volume contamination, which is particularly problematic in cortical gray matter and tissue adjacent to ventricles. Here, we demonstrate a free water elimination method to remove the CSF signal from μFA measurements in four healthy volunteers.