Thanks very much for explaining this Bruce. Tudor
On 21 May 2014 22:01, Bruce Fischl fischl@nmr.mgh.harvard.edu wrote:
Hi Tudor
- The smoothing we do is along the surface, so no matter how huge the
kernel gets it only ever includes cortical gray matter. In contrast, volume smoothing kernels will happily smooth in white matter, skull, csf, the bore of the scanner, etc.... as the kernels get big.
- Yes, we have a template, but it is a geometric one and not simply an
average, so part of the advantage is higher dimensional nonlinear warping (which also exists in the volume), but part is that we register based on cortical folding patterns not image intensities, so folds are much more likely to align across subjects (and architectonic areas as well)
cheers Bruce
On Wed, 21 May 2014, Tudor Popescu wrote:
Hi all,
If I understand correctly, the surface-based morphometry (SBM) done by Freesurfer offers superior registration as compared to voxel-based methods such as VBM, in that:
- "SBM smoothing respects anatomical boundaries better than the 3D VBM
smoothing". 2. "SBM group analysis employs inter-subject alignment based on the patterns of sulci and gyri, as opposed to Talairach registration, which often ignores sulcal/gyral landmarks"
I'm not sure I understand those reasons, however. For 1., why does the smoothing operation (basically, a multiplication) "care" about anatomy or registration at all, such that it can be said it is better done in SBM vs VBM? And for 2., doesn't the Talairach registration used in VBM simply imply a certain target template? Surely such a template is used in SBM registration as well, and if that is the case, then how are sulcal/gyral landmarks taken into account?
Thanks for any help!
Tudor
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