Thank you Doug, One more question please. Noise: does this mean low quality /high quality T1 images regarding SNR and contrast between white and gray matter. What is the correct approach to check noise effect on the reconstructed T1 images to avoid these controversies between cortical and volumetric measures ?
Thank you for any advice!
You are speaking statistically, I assume? Ie, you see a sig change in volume and not thickness, or vice versa? If so, it can easily be explained by differences in noise
On 5/2/17 5:00 AM, John Anderson wrote:
-------- Original Message -------- Subject: Re: Volume vs cortical thickness Local Time: May 2, 2017 5:00 AM UTC Time: May 2, 2017 9:00 AM From: John.anderso@protonmail.com To: freesurfer@nmr.mgh.harvard.edu freesurfer@nmr.mgh.harvard.edu
Hi Doug, Thank you for the detailed explanation! Please I have one follow-up question and I highly appreciate your input How can we explain results related to reduce cortical thickness and normal gray matter volume. Are these parameters two different thing or they are related to each other.? In other words: If (cortical thickness = gray matter volume * area ) that means reduce cortical thickness must be accompanied by reduce gray matter volume and vice versa. My question is: Have you seen similar cases for a reduction in cortical thickness and normal gray matter volume. I f yes how can this, at least, be explained mathematically.
All the best, John
The thickness is an average of two numbers. One is the distance from a white surface vertex to the pial surface along the normal to the white. The other is the distance from the pial to the white along the normal to the pial.
Volume (in v6) is computed as the volume of a truncated tetrahedron. Prior to v6 it was surface area times thickness
-------- Original Message -------- Subject: Volume vs cortical thickness Local Time: April 10, 2017 12:24 PM UTC Time: April 10, 2017 4:24 PM From: John.anderso@protonmail.com To: freesurfer@nmr.mgh.harvard.edu freesurfer@nmr.mgh.harvard.edu
Dear Freesurfer experts, I highly appreciate if anybody clarify how Freesurfer calculate cortical thickness and gray matter volume. If the cortical thickness of e.g. precentral gurus is measured as the closest distance from the gray-white boundary to the gray-CSF boundray at each vertex on the tessellated surface (Fischl and Dale. 2000). How the gray matter volume for the precentral gyrus was measured? Thank you for any clarification! John Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer -- Douglas N. Greve, Ph.D. MGH-NMR Center gr...@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 www.nmr.mgh.harvard.edu/facility/filedrop/index.html Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer 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 Partners Compliance HelpLine at http://www.partners.org/complianceline . 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.