It seems like the issue of whether or not to correct the volume when mapping to fsaverage is akin to the choice of "modulated" vs. "non- modulated" VBM, as it's called...
-MH On Tue, 2009-02-17 at 13:17 -0500, Nick Schmansky wrote: > Devdutta, > > The 'area' of a vertex on a surface in freesurfer is just the average of > the area of the triangles which touch that vertex . > > The volume data associated with a vertex created for a subject is not > buggy in how it is calculated now. it is the area of the mid-point > between the white and pial surfaces times the thickness at the vertex. > The question that has been bandied about internally is whether this > volume calculation should be corrected when it is mapped to the > fsaverage surface during a group analysis (qdec does this mapping of the > volume calcs of each subject to the fsaverage surface, when you select > 'volume' as one of the measures). At some point we will visit this > issue (and determine if it is an issue) but other stuff seems to take > priority. Maybe someone on the list can chime in. > > Nick > > On Tue, 2009-02-17 at 11:28 -0600, Devdutta W wrote: > > Hi, > > In Qdec, what exactly does the area option measure? As I understand, > > qdec does its calculations vertex by vertex, which makes sense in case > > of cortical thickness. But if area refers to surface area how does > > that change from vertex to vertex? Or is it calculating the area by > > ROI? Is my understanding of this correct? > > > > Also, as regards to the volume option, I was told that it is not > > working. But when I ran it it seems to work fine. Should I take that > > to mean that the calculation has bugs and that the results it displays > > are incorrect? Or has it been fixed? > > > > I greatly appreciate any help in this matter. > > > > Thank you, > > Devdutta > > _______________________________________________ > > 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 _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
