Hi John,
The registration works well. When I open the "target" axial(T1) and the
registered "source" (mean_EPI) in the check registration of SPM the
registration is good.But since I've resliced the source I hoped to see the
origin of the source at [0 0 0] the same as the target.
Also ,one more thing ,Why does SPM change the origin of my EPI images
after realignment? My EPI images were at origin [0 0 0] before realignment
but origin becomes [33 33 11] after realignment.
One more intersting observation is if I interchange the source and target
the axial T1 origin shift to [33 33 11] which is correct.
Regards
--Sachin
Sachin Jambawalikar
Dept Of Biomedical Engg
SUNY STONY BROOK
On Fri, 21 Nov 2003, John Ashburner wrote:
>
> > I'm trying to co-register functional T_map with the axial(T1).
> > I used the axial as target. The meanEPI as the fisrt source and the T_maps
> > as the other source images.
> >
> > I'm skipping the normalization step for both functional and Axial images.
> >
> > my axial dim [256 256 30] vox[0.82 0.82 3.00] origin[0 0 0]
> > my mean & T_maps dim [64 64 21] vox [3.59 3.59 3.00] origin[33 33 11]
> >
> > After co-registration the orign voxel for the T_maps and meanEPI should
> > have been at[0 0 0] but strangely it is at [131 134 13].
>
> An origin of [0 0 0] actually refers to the centre of the volume in SPM.
> When you coregister your images, the "source" and "other" images are moved
> to reflect the new positions. The exact positions are written into the
> .mat files, but the origin field is used to store the new approximate
> origin of the images.
>
> Did the coregistration actually work? If the starting estimates were bad,
> (more than about 3cm apart), then mutual information registration registration
> may cause the images to drift apart, rather than come into register. Try
> the "check reg" button, to see what has happened.
>
> Best regards,
> -John
>
> --
> Dr John Ashburner.
> Functional Imaging Lab., 12 Queen Square, London WC1N 3BG, UK.
> tel: +44 (0)20 78337491 or +44 (0)20 78373611 x4381
> fax: +44 (0)20 78131420 http://www.fil.ion.ucl.ac.uk/~john
>
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