Hi,
You are correct in saying that the search direction ('perpendicular'
to the local skeleton) is determined purely by the local gradient (and
second derivative) of the FA, and not taking into account tensor
eigenvalues. There are many other sources of information that can
potentially aid the registration, including the eigenvectors, but
we've concentrated on what seems to matter the most.
I wasn't sure what your actual question was?
Cheers.
On 24 Jul 2009, at 19:52, Hedok Lee wrote:
> Dear FSLers,
>
>
> I have a general question about projecting skeltonized FA onto a
> template.
>
> From what I understand projection of the skeltonized FA is performed
> by
> displacing skeltonized voxels to match a template skleton. This step
> is done
> by using a position of voxel and its FA, but it does not take into
> account
> for the direction of principal eigen vector in the voxel. In other
> word,
> when principal eigenvector is weighted with FA map, we can color-
> code a
> voxel with FA and its orientation (Red, Green, and Blue), so the
> projection
> should be done by matching not only FA but with its orientation as
> well
> (being homologous may be the right term ?).
>
> I think this also applies to skeltonizing step too.
>
> Perhaps, I’m missing something here. Let me know if anybody has any
> opinion
> on this.
>
> Thanks,
>
> 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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