Hi,
On 1 Mar 2008, at 02:07, Marenco, Stefano (NIH/NIMH) [E] wrote:
> Our analysis outputs empty maxc_tstat1.nii.gz and
> maxc_tstat2.nii.gz (max=0)
> Is this the expected result for a negative finding (no significant
> clusters) or did we do something wrong?
If you check your raw _tstat images and see if there are any voxels
above the cluster-forming threshold that you used in randomise, you
should be able to see if there were any clusters that should have p-
values in the maxc outputs.
> Also, we are working on TBSS results. Regardless of the source of
> the data, it is my understanding that variance smoothing is always a
> good thing to do. Is this correct? Is there a rule of thumb on how
> much variance smoothing should be applied (e.g. twice the voxel
> resolution)?
There's no clear rules on this I'm afraid. As Tom said recently, it is
most useful for when you have a small number of subjects. You might
alternatively consider using TFCE in randomise; we have not yet
optimised the TFCE settings for TBSS-processed data, although you
might try using --tfce_H=1 --tfce_E=1 --tfce_C=26
Cheers.
> Stefano Marenco, MD
> NIMH/GCAP
> Building 10, room 4S235
> 10 Center Drive
> Bethesda, MD 20892
> tel: 301 435-8964
> fax: 301 480-7795
> email: [log in to unmask]
>
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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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