Dear list,
 
Recently, at our lab we switched from optimised VBM to DARTEL to perform spatial preprocessing in voxel-based morphometric studies, as it should give cleaner results. However, we have noticed that replicability of Dartel vs. optimised VBM is not too good in several data sets in which we compared samples of psychiatric patients to healthy controls (there was a previous post http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind0806&L=SPM&P=R15164 for Parkinson patients vs. controls). Specifically, we have two fairly large, independent samples of n=105 (55 patients vs. 50 healthy controls) and n=142 (99 vs. 43); in the first we found robust results (at a corrected threshold, in expected brain regions) for optimised VBM, which we were unable to replicate when using Dartel (with either 8 or 12 mm FWHM smoothing). In the second, highly significant results obtained when using Dartel could not be replicated - not even remotely - with VBM. In both studies, analytical models for VBM and Dartel were identical. The templates created by DARTEL (template_6 (both grey and white matter)) look fine, as did the normalized grey and white matter images per subject (mwrc1xxxx.nii/mwrc2xxx.nii).
 
Do others have similar experiences? Any thoughts?

 

Best,

 

Odile van den Heuvel, Marie-José van Tol & Dick Veltman.

 

Department of psychiatry, VUmc, Amsterdam, the Netherlands.