Yes, I think so. One hemi will be systematically different than the other, and this can easily be picked up in the stats
On 03/23/2017 10:07 AM, Dorian P. wrote: > Thank you Douglas. > > I understand the rigor needed in the analysis and I agree. One more > question for my curiosity. > > My thickness maps are smoothed at 10mm before transferring in > fsaverage space (mri_surf2surf --fwhm-src). After all this smoothing, > does it still matter the subtle effects of interpolation on one > hemisphere and not the other? > > Dorian > > On Wed, Mar 22, 2017 at 1:32 PM, Douglas Greve > <gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu>> wrote: > > A simple LR registration on fsaverage is not ok because you would > be resampling one hemisphere and not another. The resampling > inevitably incurs some interpolation so one hemi would be smoothed > more than the other which would cause bias. If you just want > something quick, then you can sample your fsaverage surfaces to > fsaverage_sym (the registration has already been done in v6), then > just follow the steps in the wiki using fsaverage as your subject > name. I have not tested whether this is the same as doing the full > xhemi process, so I would not use the results in publication. But > probably they won't change much. > > > On 3/20/17 2:36 PM, Dorian P. wrote: >> Hi all, >> >> I have a bunch of thickness files in fsaverage space (already >> smoothed at fwhm). >> I was wondering whether is possible to compute quickly an >> asymmetry overlay for each one, but it's turning more difficult >> than I thought. Vertex indices are different between lh and rh. >> So I started looking at fsaverage_sym, which has already >> registrations lh-rh. I thought this would be a nice shortcut to >> avoid registering every subject again. But there are a couple of >> confusing points: >> >> 1. Why isn't lh.inflated well aligned between fsaverage and >> fsaverage_sym (see figure below) ? >> Inline image 1 >> >> 2. I found an old post in 2012 >> >> <https://mail.nmr.mgh.harvard.edu/pipermail/freesurfer/2012-December/026957.html>, >> in which Donald advises to not run analyses on a simple >> left-right registration because one hemisphere would be more >> processed than the other. Since I might want to run some >> analyses, can you please explain what is the best way to get >> asymmetry surfaces (possibly by avoiding new registrations)? Why >> wouldn't a simple L-R registration of fsaverage be ok? >> >> I run the analyses in R and don't necessarily need the glm tools >> within FS. >> >> Thank you in advance. >> Dorian >> >> >> _______________________________________________ >> Freesurfer mailing list >> Freesurfer@nmr.mgh.harvard.edu >> <mailto:Freesurfer@nmr.mgh.harvard.edu> >> https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer >> <https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer> > _______________________________________________ Freesurfer mailing > list Freesurfer@nmr.mgh.harvard.edu > <mailto:Freesurfer@nmr.mgh.harvard.edu> > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > <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 > <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
