Comparison of corticospinal tract integrity measures extracted from standard versus native space in chronic stroke

Fractional anisotropy (FA) and mean diffusivity (MD) are measures derived from diffusion-weighted imaging that represent the integrity of the corticospinal tract (CST) after stroke. Some studies of the motor system after stroke extract FA and MD from native space while others extract from standard space making comparison across studies challenging.

The purpose was to compare CST integrity measures extracted from standard versus native space in individuals with chronic stroke. Twenty-four individuals with stroke underwent diffusion-weighted imaging and motor impairment assessment. The spatial location of the CST was identified using four commonly utilized approaches; therefore, our results are applicable to a variety of approaches.

FA extracted from standard space (FA_std) was significantly different from FA extracted from native space (FA_nat) for all four approaches; FA_std was greater than FA_nat for three approaches. The relationship between ipsilesional CST FA and UE FM was significant for all approaches and similar regardless of extraction space. MD_std was significantly different from MD_nat for most approaches, however, the directionality of the differences was not consistent.

Our study shows that extraction space influences diffusion-based microstructural integrity values (FA and MD) of the CST in individuals with stroke, which is important when considering methods for aggregating CST integrity data across studies. The relationship between CST integrity and motor impairment appears to be robust to extraction space.

The differences we identified are important for comparing FA and MD values across studies that use different extraction space. Our results provide context for future meta-analyses of diffusion-based metrics of CST integrity in individuals with stroke.