Dear FSL experts,
I have a diffusion data set with
3 groups, 2 time points each (pre&post training), and want to see,
for each group, where there are changes in FA from pre
to post, and also where these changes differ between the groups (i.e.
time x group interaction), while controlling for age and gender.
I know that for VBM, the image fed to randomise is created by subtracting the 4D merged®istered image corresponding to the pre scans from that of the post scans, and then manually smoothing it. However, I haven't found a similar guide for TBSS on the wiki and in the list archives.
I am wondering:
1) How is the difference image created exactly?Is the subtraction made for the FA values themselves (i.e. are the individual images are the dti_FA images) or for the skeleton (e.g. all_FA_skeletonised)?
2) At which stage should this subtraction be performed, e.g. before bedpostx, before tbss_1_preproc etc ?