SPMers,
I'm trying to do a simple volumetric analysis of WM, GM and CSF using
segmentation in SPM2 and have some questions after experimenting a bit with
it. We find that we get very different results with N vox depending on
whether the brain is extracted first or not or if we input normalized images
or not.
1. Is it recommended to extract the brain first?
2. What is N vox giving us? If it is the proportion of intracranial volume
accounted for by WM/GM/CSF, why don't the numbers add to 1 consistently?
3. For the most accurate segmentation and estimates of proportions of
GM/WM/CSF, resp. of ICCV, should the non-normalized MPRAGE or normalized
MPRAGE be used? Clearly resolution of the resliced, normalized images
matters as well because of partial voluming and interpolation errors
4. Is there a substantial difference between SPM2 and SPM5 with respect to
segmentation?
Thanks for any help on this,
Randy Benson
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