Hi,
It's not clear how your design relates to your "20" drug/placebo
timepoints - however maybe this is answered by my previous email,
about FMRI contrasts-of-contrasts?
Cheers.
On 17 Feb 2009, at 00:27, Michael Scheel wrote:
> 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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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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