Hi - you're right - the FMRI motion correction in both FSL and SPM apply
6DOF - i.e. rigid body transformations. You're also right in stating that
this will not correct for motion during each volume's acquisition. As far
as I know there is no publicly available software to correct for this
more subtle problem, although we are working on a solution (ie 4D motion
correction); though we can't make any promises yet! WRT testing for
whether this is a problem in a dataset, it's not trivial, though you could
look at MELODIC (ICA in FSL) output to look for motion-related components
after motion-correction.
Thanks, Steve.
On Fri, 27 Sep 2002, carles wrote:
> Dear colleagues,
>
> I am writing to both SPM and FLS mailing list. Sorry for those who have
> received this message twice.
>
> I have some questions about registration of volumes in fmri. As I understand
> both programs are doing this registration appliying 6- parametre
> transformations, that is, considering the brain as a rigid solid. However,
> taking in account the ratio TR/delay the most probable is that movements are
> produced during volume acquisition instead between two acquisitions. In this
> case, different slices should be not parallel so the whole brain is deformed
> in a way that it can't be recovered by any affine transformation (neither a
> 12-parameter one). I agree that if pacient's movements are very slow this
> deformation may be irrelevant but short movements are usual (as it can be
> seen in registration graphs).
>
> My questions are: Should registration be done slice by slice in orther get
> more accuracy? In that case, is there any tool to reslice a volume from non
> parallel slices? And finally, is there any way to measure if brain
> deformation produced by pacient's movement during acquisition is relevant or
> not (quality assurance of data)?
>
> Thanks for your attention
>
> Yours,
>
> Carles Falcon
> Hospital Clinic Barcelona
> University of Barcelona (Spain)
> [log in to unmask]
>
Stephen M. Smith
Head of Image Analysis, FMRIB
Oxford University Centre for Functional MRI of the Brain
John Radcliffe 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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