Hello Dennis,
I guess you have noticed John's answer saying that modulation while producing
the priors is not recommended.
I do not have a really logical explanation for the discrepancy you describe
between the results using different priors.
However, the difference must lie in the segmentation step.
You could investigate if your GM was (mis)classified as WM in the technically
proper analysis - either by looking at WM maps or summing modulated WM and GM
maps. We observed this type of 'segmentation shift' in Huntington"s disease
when deep grey matter nuclei correctly 'disappeared' but re-appeared as
increased WM volume.
Best regards,
Philipp G. Saemann
Max-Planck-Institute of Psychiatry
NMR Study Group
Kraepelinstr 2-10
80804 Munich
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