Hi Tudor
1. 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.
2. 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:
1. "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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