for the continuous curvature you can just cite the FreeSurfer paper, or recon1/2). For the discrete curvature I think Rudolph Pienaar published something on it. Some of the curvature indices are from David Van Essen's papers, and the volume/area calculation is Anderson M. Winkler's paper

cheers
Bruce


On Mon, 9 Sep 2019, Loske, Philipp wrote:


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Hi you two,

thank you very much for your quick reply! Just two short followup questions:

@Bruce: Is this published in any paper or documentation so I can cite it?

@Doug: Has this method been implemented with the last release of FS in 6.0.0
or already before in 5.3.0 (I'm still using this version)?

Cheers
Philipp

      For cortical volume we compute  vertex-wise volume based on
      dividing each obliquely truncated   trilateral pyramid into
      three tetrahedra. Based on Anderson M. Winkler's   srf2vol
      matlab script.
On 9/6/2019 10:22 AM, Bruce Fischl wrote:
Hi Philipp

I'll leave the volume question to Doug. The curvatures are estimated
by fitting a second order polynomial to the local height function in
the tangent bundle then computing the Hessian using the white
(gray/white boundary) surface. We also have some discrete measures of
curvature that uses the Gauss-Bonnet theorem, but those aren't run by
default.

cheers
Bruce
On Fri, 6 Sep 2019, Loske, Philipp wrote:


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Hello FreeSurfer Developers,


I have a question about references and descriptions to all the
morphological
features available in aparc.stats, extracted from structural MRI. I am
using
all the different features (SurfArea, GrayVol, ThickAvg, ThickStd,
MeanCurv,
GausCurv, FoldInd, CurvInd) for the 68 cortical regions available from
the
Desikan Kiliany atlas. I have been trying to find references to how
these
features are measured or derived, but couldn't find a proper list of
references to each of the features. I a lot of references
here
https://surfer.nmr.mgh.harvard.edu/fswiki/FreeSurferMethodsCitation,
with detailed descriptions on surface reconstruction and how cortical
thickness is measured, but couldn't find a detailed explanation on the
other
features, especially curvature values.

I think I have been able to find out what each of the measurements
mean and
how they are calculated in principle, through searching the internet a
lot,
but with no direct link to FreeSurfer. For instance, I know you can
calculate
the curvature values from the principle curvatures, but how does FS
estimate
those form the reconstructed Surface? And which one of the two
surfaces does
it use? White-pial or pial-csf surface? I found https://brainder.org/
really
helpful, but it says for example that a new way of measuring cortical
volume
was implemented in FS 6.0.0, so does that mean for previous versions
FS uses
the Thickness x SurfaceArea method? Would be great if you can help me
with
this, or point me to the correct website I might just have missed
during my
search.


Best wishes

Philipp




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