Hello MRtrixers,

First off thanks for providing the fixel-based analysis framework & documentation, I was able to implement this successfully for a cross-sectional study. Soon I will be attempting to use this framework using longitudinal data, and was wondering if this is currently possible using the existing statistical framework?

My question is more around implementing *fixelcfestats* for the statistical comparisons. For example, in FSL you can set up your GLM to handle repeated measures by either setting up a paired t-test to test a group difference (which I guess might be possible in CFE), but for a group-difference over time the 4D input file is subtracted over time (e.g. <all_FA_time2 - all_FA_time1>) to test a group difference over time. Given the input for *fixelcfestats* are individual fixel images, is it possible to generate this ‘subtracted’ fixel? I imagine this might get tricky when dealing with different fibre directions over time…

I think maybe the other option would be to generate whole-brain AFD maps and subtract them over time for a voxel-wise analysis, but I guess the voxel-averaged measure wouldn’t be specific to individual fibre populations. However, if this is the only way to do it at this stage - would it be feasible?

Thanks in advance, looking forward to hearing your suggestions!

Sila