Hi James,
just a hunch, but it looks like there is a brain in there after all ;)
which may match the "normal" volume as derived from your group (there
seems to be a "haze of activation" around it if you check the sagittal
view). I would think that the brains are correctly normalized but what
you see is "smoothed out" activation because you have not set a lower
absolute threshold which is recommended for VBM studies. Try excluding
voxels with a value of below, say, .1, and see if your effect is still
present.
Hope this helps,
Marko
James Osterberg wrote:
> Dear all
>
> I have used DARTEL-VBM to examine differences between a disease group
> and control group.
>
> To check the boundaries of the final processed brains I have compared
> groups using a very low contrast (p=0.3). However, the boundaries of the
> brain are clearly outside of the normal area - see attached picture.
>
> I used default settings for DARTEL.
> The voxel size was correctly specified (and was 0.9).
>
> Can anyone explain where I have gone wrong? Or how I might go about
> troubleshooting this?
>
> Many thanks
>
> James
>
>
>
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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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