[pymvpa] Preprocessing in FSL, question on specifics

Michael Hanke mih at debian.org
Tue Jul 12 23:32:40 UTC 2011

On Tue, Jul 12, 2011 at 04:50:04PM -0500, J.A. Etzel wrote:
> Volume order within a session definitely matters: I had a dataset in
> which the volumes were entered in the wrong order (due to a
> numerical vs. alphabetical file naming mixup) and the motion
> correction was extremely abnormal and poor. Once the file naming was
> fixed the motion correction looked fine.

According to my experience, most software uses some sort of running
guess on the transformation matrix with heavy constraints on the
translation/rotation magnitude between volume (for speed reasons).
Reverse order of volumes shouldn't have much of an effect, but random
order would. For heavy between session motion (maybe people got out of
the scanner) it might be better to compute a cross-session alignment and
combine that with within session motion correction. But again, that is
nothing MVPA specific.


Michael Hanke

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