The FS segmentation is a combined segmentation and registration to an atlas space. This is probabilistic in that the atlas is built from 40 subjects and uses intensity, location, and neighborhood priors. I think VBM is using unified segementation which performs intensity normalization, segmentation, and registration simultaneously also using a probabilistic atlas. VBM segments GM/WM/CSF whereas FS segments various GM and ventricular structures as well as WM. VBM is a voxelwise analysis which is registered to an atlas, modulated, and spatially smoothed, all of which will have strong effects on the results. Maybe a VBM expert on the list can chime in with more info.
doug On 11/05/2013 08:08 PM, jh kim wrote: > Dear Drs. Bruce and Doug > Thanks for the valuable comments. > > Discrepancy between FS and VBM lies in putamen and hippocampus. > Would you please briefly comment regarding segmentation method of > above structures in FS? > I'm just wondering whether segmentation of grey matter in FS is > largely different from that of VBM? > Sorry for bothering you again with my silly question. > > Thanks. > Kim > > > 2013/11/5 Douglas N Greve <gr...@nmr.mgh.harvard.edu > <mailto:gr...@nmr.mgh.harvard.edu>> > > > 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 > <mailto: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 <mailto:gr...@nmr.mgh.harvard.edu> > Phone Number: 617-724-2358 <tel:617-724-2358> > Fax: 617-726-7422 <tel:617-726-7422> > > Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting > <http://surfer.nmr.mgh.harvard.edu/fswiki/BugReporting> > FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 > www.nmr.mgh.harvard.edu/facility/filedrop/index.html > <http://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 <mailto: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. > > > > > _______________________________________________ > 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
