FA isn't typically associated with gray matter volume so I don't think this would have to be accounted for in the analysis.

However, since the reviewer asked, one way to compute in FSL is to use FAST to segment the structural scan into GM, WM and CSF, then sum all values of the GM partition, which can be done with fslstats (fslstats will give the average GM and also the number of voxels; multiplying the two gives the total volume then).

All the best,

Anderson

On Tuesday, 21 November 2017, Lim, Lena <[log in to unmask]> wrote:

Dear Anderson/FSL experts,

I am doing a DTI TBSS and Tractography analysis. I was wondering if I need to control for the total grey matter volume (as suggested by a reviewer) in the brain and if so, how do I get the values in FSL please?

Many thanks,

Lena