Hi - I would instead use the summary measure of mean (across all
voxels) mm displacement that you can easily get by feeding the affine
matrix and an identify matrix into "rmsdiff"
Cheers.
On 7 Nov 2008, at 22:23, Hedok Lee wrote:
> Dear FSLers,
>
> I’ve been analyzing FA using TBSS to compare 2 groups (controls vs
> patients)
> and got expected results. I then began wondering whether groups
> differences
> in FA were simply due to excess motion during the scan since our
> patients
> were diagnosed with a movement disorder, and head movement is
> inevitable in
> our study.
>
> So I had an idea of extracting rotation matrix from
> “eddy***.ecclog” file
> and enter them as additional covariate in TBSS.
>
> The problem is that the eddy correction is affine transformation and
> decomposed rotation matrix by “avscale” is not unique.
>
> I’m kind of stuck with this idea, and am wondering whether I should
> abandon
> this idea of having additional covariate. I appreciate if someone
> has an
> opinion about this kind of approach.
>
> Also, if there is any paper written about effect of motion induced
> false-positives in voxel-wise DTI analysis, please let me know.
>
>
> Thanks in advance,
>
> Hedok
>
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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)
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