I'm a SPM beginner and am using DARTEL for a VBM5.1 analysis in one group of subjects. I want to correlate behavioural scores with Gray matter and White matter volumes of fmri structural data. My Statiscal model: Multiple regression = 1 covariate of interest (behavioural score), 3 covariates of no interest (sex, age, TIV) = 1 or -1, 0, 0, 0.
After reading many emails in SPM list, it persists for me 3 questions about differents stages:
1) Segmenting: I thought realize 1 segmentation (GM an WM in native space with bias corrected), but read it was better to do twice (one segmentation bias corrected YES, then another segmentation bias corrected NO with new images produced). I find it odd, is it really better ?
2)Calcul TIV: I segment GM and WM tissues. I obtain TIV (GM, WM, CSF) with "calculate raw volumes for GM/WM/CSF" button in VBM5.1 tools. I don't understand how VBM can calcul CSF volumes without CSF segmentation images. Do you confirm i use only GM+WM volumes ?
3)Regression analysis with White Matter: which is the moment i have to treat WM images differently of GM images ? > I do a specific template for WM volumes OR i do 2 regression (one with GM scans [smmwrc1ms*.nii], another with WM scans [smmwrc2ms*.nii°]) OR i do one regression (GM scans then WM scans in the same order) ?
I know that these questions aren't very important, but i want to do a suitable analysis.
Excuse my bad english. Thanks a lot !
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