Hi Haakon,
just a hunch as your images even by visual inspection seem rather
inhomogeneous: try writing out the bias-corrected images during
segmentation and use these as the target for your EPI. Perhaps the
coregistration gets caught up on the inhomogeneity gradients (which
would explain the shift in one direction only). I had similar problems
several years ago with high-field data and using the bias-corrected
images helped.
Good luck,
Marko
Haakon Engen schrieb:
> Dear SPM'ers,
>
> I realize questions as basic as how to get coregistration to work are a
> few notches below what usually gets answered on this list, but I'm
> really at my wits end here.
>
> The problem is that 4 (out of 27) of my subjects plainly refuses to have
> their T1 images coregistered to the mean EPI image, or any other EPI
> image for that matter. The experiment totals 4 runs, and I've tried to
> coregister the T1 to all of the mean images post- realignment, as well
> as multiple ordinary, realigned, images. I've also tried to coregister
> the EPI's to the T1, once again without success.
>
> I've attached the coreg output files for all 4 subjects. As you can see
> they all seem to be out of alignment in the Z- dimension, with the T1
> consisently lower than the EPI's, while otherwise seemingly in OK
> registration.
>
> I've tried fiddling around with the settings, changing objective
> functions, seperation and tolerances without much success. I've also
> tried using the coregister and reslice function, with interpolations
> from trilinear up to 7th degree spline- again without success. This is
> rather troublesome as this means that the normalization parameters
> calculated by the unified segementation procedure are similarly shifted,
> which results in "extracranial" activations, when overlaid on the
> glassbrain.
>
> Can anyone give me a clue as to why this happens, and how to fix or work
> around it?
>
> I'm on a Vista x64 workstation using Matlab R2007b, and SPM 8b r2598.
>
> Kind regards,
>
> Haakon G. Engen
> Research assistant
> University of Oslo
>
>
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--
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Marko Wilke (Dr.med./M.D.)
[log in to unmask]
Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
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