Matrix design with subsample

Hello MRtrix experts

Happy new year !
I computed a FBA between two groups (15 patients versus 30 healthy individuals) in line with the recommended pipeline. The observed findings are very interesting.
Secondary to the whole brain FBA, I 'm trying to perform correlation analysis but I have values only for my patients (n = 15) and not for healthy individuals.
Is it possible to investigate the correlation analysis only for my patients even if my group-specific template was created with 15 patients and 15 healthy individuals ?
Can fixelcfestats be used for this context ?
If yes, could you please explain me how ? What is the design matrix please ?

Many thanks in advance for your time and thank you so much for this very helpful forum !!!
Best regards,



I think you should be able to do that regardless of the template yes, as the pipeline does not rely on the template at this stage, that only has to do with how you processed the fixel data.

I have not tried myself but I don’t think all participants need to be included for fixelcfestats to work (the number of rows in the design matrix should match your inputted files.txt list though). You could try to make a design matrix with an intercept column made of 1s, no group column this time, and only your patient rows. The model should then test the effect of the IV you want to test across the participants in the rows.

Maybe this thread can help:


Hi Charly,

Thank you so much for take your time to me reply in details.
I will follow your explanations very helpful to compute my design matrix with a subsample. It’s work very well.

Have a good day,