Hi Jürgen
in some ways you can think of it as a partial volume correction. We know the cortex is smooth at the spatial scale of a couple of mm, and so impose this constraint to estimate the location of the surface with subvoxel accuracy. In addition, if a given voxel is darker than it's neighboring gray matter voxels it probably contains more CSF so the surface should be a bit further in than if the voxel were brighter.
I hope that helps Bruce
On Thu, 5 Jan 2012, Jürgen Hänggi wrote:
Dear FS experts
We have the following request from one reviewer:
"Provide more detail and more discussion on why the thickness maps produced by FreeSurfer are not limited to the voxel resolution of the image. This is not obvious to everybody who is not an expert in cortical thickness measurements using the free-surfer approach, since it is not so easy to comprehend that differences can be found that are beyond the resolution of the acquisition."
I can provide the references that provide this statement, but I do not really have a sound explanation why this is possible.
Any idea is welcome and appreciated
Thanks in advance Jürgen
Jürgen Hänggi, Ph.D. Division Neuropsychology Institute of Psychology University of Zurich Binzmuehlestrasse 14, PO Box 25 8050 Zurich, Switzerland 0041 44 635 73 97 (phone office) 0041 76 445 86 84 (phone mobile) 0041 44 635 74 09 (fax office) BIN 4.D.04 (office room number) j.haenggi[at]psychologie.uzh.ch (email) http://www.psychologie.uzh.ch/neuropsy/ (website) http://www.juergenhaenggi.ch (private website)
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