In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative?
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Hello, Fs In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative？ by the way, how the mean curvature reflects the degree of fold? Since the mean curvature is a local measurement, does the mean curvature map reflects the fold degree?
Sulc is the integrated dot product of the movement vector with the (outwards pointing) surface normal during inflation. In gyral regions the movement vector is consistently inwards and has a negative dot product with the surface normal, which is why it is negative.
As for your second question, I’m not sure I understand. The mean curvature is the average of the two principle curvatures. If you think of the surface locally as a height function over the tangent plane, then the two curvatures are the eigenvalues of the Hessian of that function (if that helps).
Cheers Bruce
From: freesurfer-bounces@nmr.mgh.harvard.edu freesurfer-bounces@nmr.mgh.harvard.edu On Behalf Of 1248742467 Sent: Monday, June 14, 2021 9:23 PM To: freesurfer freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative?
External Email - Use Caution Hello, Fs In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative？ by the way, how the mean curvature reflects the degree of fold? Since the mean curvature is a local measurement, does the mean curvature map reflects the fold degree?
Maybe a better way to think about curvature is that it indicates whether the surface is locally above (positive) or below (negative) the tangent plane
On Jun 14, 2021, at 10:29 PM, Fischl, Bruce BFISCHL@mgh.harvard.edu wrote:
Sulc is the integrated dot product of the movement vector with the (outwards pointing) surface normal during inflation. In gyral regions the movement vector is consistently inwards and has a negative dot product with the surface normal, which is why it is negative.
As for your second question, I’m not sure I understand. The mean curvature is the average of the two principle curvatures. If you think of the surface locally as a height function over the tangent plane, then the two curvatures are the eigenvalues of the Hessian of that function (if that helps).
Cheers Bruce
From: freesurfer-bounces@nmr.mgh.harvard.edu freesurfer-bounces@nmr.mgh.harvard.edu On Behalf Of 1248742467 Sent: Monday, June 14, 2021 9:23 PM To: freesurfer freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative?
External Email - Use Caution Hello, Fs In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative？ by the way, how the mean curvature reflects the degree of fold? Since the mean curvature is a local measurement, does the mean curvature map reflects the fold degree?
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To add to the explanation from Bruce:
It's easy to remember the sign of 'sulc' if you know that it is an abbreviation for 'sulcal depth' -- in that case it makes sense that it is negative for gyri.
Regarding curvature, if you do not have a background in math/physics, I would suggest to read the excellent Wikipedia articles on that (https://secure-web.cisco.com/1eM5ABlxLFULXpIV8y-bbSb1GhHvFGo1EsI-SHSsD8aFOLx...). Also read the related ones (for mean curvature, Gaussian curvature, and the one about principle curvatures). Afterwards it will be very clear.
Tim
-- Dr. Tim Schäfer Postdoc Computational Neuroimaging Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy University Hospital Frankfurt, Goethe University Frankfurt am Main, Germany
On 06/15/2021 4:53 AM Fischl, Bruce bfischl@mgh.harvard.edu wrote:
Maybe a better way to think about curvature is that it indicates whether the surface is locally above (positive) or below (negative) the tangent plane
On Jun 14, 2021, at 10:29 PM, Fischl, Bruce BFISCHL@mgh.harvard.edu wrote:
Sulc is the integrated dot product of the movement vector with the (outwards pointing) surface normal during inflation. In gyral regions the movement vector is consistently inwards and has a negative dot product with the surface normal, which is why it is negative.
As for your second question, I’m not sure I understand. The mean curvature is the average of the two principle curvatures. If you think of the surface locally as a height function over the tangent plane, then the two curvatures are the eigenvalues of the Hessian of that function (if that helps).
Cheers Bruce
From: freesurfer-bounces@nmr.mgh.harvard.edu freesurfer-bounces@nmr.mgh.harvard.edu On Behalf Of 1248742467 Sent: Monday, June 14, 2021 9:23 PM To: freesurfer freesurfer@nmr.mgh.harvard.edu Subject: [Freesurfer] In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative?
External Email - Use CautionHello, Fs In Freesurfer, the sulc value of the gyrus is NOT positive, on the contrary, they are negative？ by the way, how the mean curvature reflects the degree of fold? Since the mean curvature is a local measurement, does the mean curvature map reflects the fold degree? _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://secure-web.cisco.com/1Eb4xq4CX3GZx_5NdnHleKfrS7lKbe8yMipvOqbtWwkLQY2... The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Mass General Brigham Compliance HelpLine at http://secure-web.cisco.com/1DZiNFukpBCOy4Kpraothv0_gN5bq4-rcWy4Q58wgEj_-cH0... . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail. Please note that this e-mail is not secure (encrypted). If you do not wish to continue communication over unencrypted e-mail, please notify the sender of this message immediately. Continuing to send or respond to e-mail after receiving this message means you understand and accept this risk and wish to continue to communicate over unencrypted e-mail.
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