On Thu, 23 Oct 2008 12:50:28 +0100, Michael Bannert
<[log in to unmask]> wrote:
>hi,
>
>i would like to know if there is a function in spm2 that does what afni's
>3ddespike does. we used to routinely run 3ddespike before motion correction
>to discard outliers...
>
>i read in rik henson's sample preprocessing script that there's an spm5spike
>function, which at least detects outliers but it is not part of spm5.
>
>(see http://imaging.mrc-cbu.cam.ac.uk/imaging/SpmBatch5 )
>
>is there a similar function for spm2 that detects and removes outliers? or
>is there a better way to deal with outliers? our experiment is on visuomotor
>systems and therefore involves some motion which is why we expect that
>outliers may be a problem for us.
What kind of "spikes" are they?
In our EPI data, I occasionally see "spikes" as bad volumes that appeared
banded: they have alternating bands of relative bright and dark parallel to the
plane of acquisition. My impression talking to MRI physicists etc is that those
are due to intravolume motion.
For _that_ kind of artifact, any attempt to "fix" the data is pretty much
hopeless. All one can do in such a case is (1) verify that it affects only a
small number of volumes, and (2) intelligently remove the volumes from the
analysis.
So...it really depends on the nature of the problem.
Best,
S
>
>thanks for your help
>michael
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