Dear SPM ers:
Using SPM99 I used no global normalization (ngn) and then ancova (anc
for global differences nuisance) on the same set of data to compare
the results.
PET data = [(n=14 subjects) voxel size 2,2,2, smoothing Gaussian
14,14,14 mm. same grand mean scaling and absolute threshold]
I found
1) mask produced by the 2 analysis was similar (visually)
2) RPV.img resels images were dissimilar. far more contrast and
variation using anc than ngn.
3) Striking differences in number of resels.
ngn smoothness fwhm 43.9, 47.6, 47.3 (mm) 1 resel = 12372.74
voxels, S=7.1 resels.
anc smoothness fwhm 15.7 17.0 17.3 (mm) 1 resel = 577.34 voxels,
S=151.6 resels.
S is 102089 for both data.
Can someone explain these large differences.
Thank you
Didine
--
Badreddine Bencherif,MD
Department of Radiology
Division of Nuclear Medicine
Johns Hopkins University School of Medicine
601 North Caroline Street / JHOC 4230
Baltimore, MD 21287-0855 USA
Voice: (410) 614-2787 Pager: (410) 283-2050
Fax: (410) 614-1977
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