I’m studying a neurodegenerative disease using the FBA framework and trying to compare the results to traditional voxel-based DTI (in a similar fashion to Mito et al., 2018).
Part of my analysis is to study the correlation between a specific clinical measure and degenerative WM changes (using both FBA and VBA). The lower this clinical measure is, the more WM degeneration is expected. FBA correlation results show exactly that, while VBA showed the same relationship but not in all tested tracts.
While I was checking both positive and negative GLM contrast results, I noticed a cluster of around 4 voxels showing a statistically significant increase in FA correlating with the decrease in the clinical measure (opposite of what’s expected).
At first I thought this could be a similar effect to what Mito et al. found with areas of crossing fibers, were an increase in FA was found in the AD group and was attributed to the tensor model failing to model crossing fibers. However, I checked the fixels in the region with the increased FA (optic radiation near the occipital pole) and couldn’t find any crossing fibers. Plus, as far as I know, this region isn’t particularly known for having crossing fibers.
Now I’m trying to find an explanation for this small area of increased FA. Could there be crossing fibers that area that was not accounted for in the fixels, due to perhaps some limitation in the data? Any idea as to why I’m getting this increase in FA?
Looking forward to hear any insight on the matter. And as always, thanks for the great software and the constant online support!