Dear fsl experts,
I have a question regarding the output of siena. We scanned 20
subjects at four different timepoints - 1) PreDrug 2) PostDrug
3)PrePlacebo 4) PostPlacebo.
I used siena to estimate atrophy/growth in both conditions (Placebo
and Drug) individually
> siena subject_predrug.nii.gz subject_postdrug.nii.gz
> siena subject_preplacebo.nii.gz subject_postplacebo.nii.gz
As suggested on the website I then did >run siena_flow2std A B< and
used fslmerge to merge all the A_to_B_flow_to_std.nii.gz into one 4D
file (all_flow_to_std.nii.gz) so that first all the 20 were flow
images between Pre and Post for the DrugCondition and the last 20 were
the changes under the Placebo Condition. I then set up matrix and
contrasts with the Glm_gui wizard to set up a paired ttest and used
randomise with the threshold-free-enhancement-option.
As the whole procedure was rather to control that there wasn't any
particular atrophy so I didn't expect any significant results.
However I do get signifant voxels for the Contrast 'Condition B >
Condition A' Contrast and was wondering how to interpret these
findings, would it mean that the atrophy is bigger in the Placebo
Condition?
Below my design matrix and contrast (example for 5 subjects)
Input Group EV1 EV2 EV3 EV4 EV5 EV6
1 1 1 1 0 0 0 0
2 1 1 0 1 0 0 0
3 1 1 0 0 1 0 0
4 1 1 0 0 0 1 0
5 1 1 0 0 0 0 1
6 1 -1 1 0 0 0 0
7 1 -1 0 1 0 0 0
8 1 -1 0 0 1 0 0
9 1 -1 0 0 0 1 0
10 1 -1 0 0 0 0 1
Contrasts
EV1 EV2 EV3 EV4 EV5 EV6
Condition A>B 1 0 0 0 0 0
Condition B>A -1 0 0 0 0 0
Thanks, Michael
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