Florent, I'm using MapIcosahedron from the SUMA package to do the spherical averaging and the distortions are visually quite striking in an area that is fairly important in this study. Here's a screen shot of the smoothwm surface after recreating it with an icosahedron mesh:
http://fmrif.nimh.nih.gov/~adamt/ridges.jpg Note the ridges along the gyrus. There is also a spike coming out of the sulcus nearby that is a little hard to see. Ziad (the developer for SUMA) also thought some sort of regional smoothing might be the best solution. If that's the consensus, we'll pursue that option. -Adam --- Adam Thomas [EMAIL PROTECTED] Functional MRI Facility, NIMH/NIH/DHHS 10 Center Dr, Room B1D708A Bethesda MD. 20892-1148 Phone:301-402-6351 Fax: 301-402-1370 -----Original Message----- From: florent segonne [mailto:[EMAIL PROTECTED] Sent: Thursday, November 10, 2005 4:51 PM To: Thomas, Adam (NIH/NIMH) Cc: freesurfer@nmr.mgh.harvard.edu; [EMAIL PROTECTED] Subject: Re: [Freesurfer] problems with spheres Dear Thomas, Looking at the file rh.sphere.asc, it seems that the problem comes from the spherical registration that generates a spherical surface with, as you said, small triangles slightly overlapping. However, these distortions should be extremely small. If you really need to get rid of them, one hacky solution would be to detect these (small) regions and to smooth them untill the overlapping edges(faces) disappear. Since these regions are small, this should not generate large metric distortions. But maybe Bruce has some other ideas. Florent ------------------------------------- Florent Segonne PhD Candidate Stata Center 32-D430 CSAIL MIT 1 617 253 2986 http://people.csail.mit.edu/~fsegonne ------------------------------------- On Thu, 10 Nov 2005, Thomas, Adam (NIH/NIMH) wrote: > > I recently noticed that some of my subject's spherical surfaces appears > to have several small, pyramid-like points on them. One example is shown > here in tksurfer: > > http://fmrif.nimh.nih.gov/~adamt/sphere.jpg > > Looking at these points in more detail in suma shows that several > triangles are folder on top of each other so that all the vertices are > on the spheres surface, but some triangles are entirely overlapped by > others. > > The spherical surface is here: > > http://fmrif.nimh.nih.gov/~adamt/rh.sphere.asc (11MB) > > And this is a close up of near node 141619 in suma: > > http://fmrif.nimh.nih.gov/~adamt/sphere_suma_zoom.jpg > > > These distortions are causing us problems with subject averaging. Is > there something we can do to fix or avoid them? > > Thanks, > -Adam > > --- > Adam Thomas [EMAIL PROTECTED] > Functional MRI Facility, NIMH/NIH/DHHS > 10 Center Dr, Room B1D708A > Bethesda MD. 20892-1148 > Phone:301-402-6351 Fax: 301-402-1370 > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer > _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
