Hi Kim, the answer is both easy and difficult. The easy answer is that they are completely different methods and will often give inconsistent results. I'm not sure what answer the reviewer will accept, and you might need to post the same question to the VBM and DARTEL crews. In your VBM analysis, I assume that you used modulation (ie, you were looking at volume and not "GM density")? VBM performs a voxel by voxel comparison and you probably smoothed by 10mm or so. Either of those could have washed out the effect. Certainly a reasonable response is that the FS analysis is for the entire ROI and and the VBM is voxelwise. Hope that help.s
doug On 11/03/2013 11:55 PM, jh kim wrote: > Dear Doug and experts > > I've analyzed structural changes of the subcortical GM by using both > VBM (DARTEL in SPM8) and subcortical volumemetric measurement using > FreeSurfer 5.1. While there is no significant volumetric difference > between the groups in VBM (corrected p<0.05), FS results showed that > some subcortical GM had significant volume reductions in patients > relative to controls (MANCOVA controlling for the effect of ICV, age, > gender, followed by Bonferroni correction). > One of the referees raised the question regarding this discrepancy > between the VBM and FS findings. > How can I cope with it? > > Thank you in advance for your help. > > Kim > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer -- Douglas N. Greve, Ph.D. MGH-NMR Center gr...@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 www.nmr.mgh.harvard.edu/facility/filedrop/index.html Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
