Dear Freesurfers,
Grey matter volumes of the same structure seem to be measured differently depending on if FreeSurfer establishes it as in the left or in the right hemisphere. For example, if I take a look at the caudal anterior cingulate in the right hemisphere and I flip the image (creating a mirror image of the same hemisphere, which will then be treated by FreeSurfer as a left hemisphere), the same structure has a totally different grey matter volume (see attachment, on the right the original and on the left the flipped version). Does anybody know what's the logic behind this and what's the best way to avoid FreeSurfer creating asymmetry between left and right hemisphere (maybe averaging flipped and non-flipped data?)
Thanks!
Kind regards, Remmelt Schür
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Hi Remmelt
folding patterns are not symmetric across the hemispheres, so the cortical parcellation will change if you flip things left/right, which is appropriate. I would be surprised if you see much change in the thickness though.
cheers Bruce
On Fri, 15 Jun 2012, Schur, Remmelt R. wrote:
Dear Freesurfers,
Grey matter volumes of the same structure seem to be measured differently
depending on if FreeSurfer establishes it as in the left or in the right hemisphere. For example, if I take a look at the caudal anterior cingulate in the right hemisphere and I flip the image (creating a mirror image of the same hemisphere, which will then be treated by FreeSurfer as a left hemisphere), the same structure has a totally different grey matter volume (see attachment, on the right the original and on the left the flipped version). Does anybody know what's the logic behind this and what's the best way to avoid FreeSurfer creating asymmetry between left and right hemisphere (maybe averaging flipped and non-flipped data?)
Thanks!
Kind regards, Remmelt Schür
IMPORTANT WARNING: This email (and any attachments) is only intended for the use of the person or entity to which it is addressed, and may contain information that is privileged and confidential. You, the recipient, are obligated to maintain it in a safe, secure and confidential manner. Unauthorized redisclosure or failure to maintain confidentiality may subject you to federal and state penalties. If you are not the intended recipient, please immediately notify us by return email, and delete this message from your computer.
To add on to Bruce's explanation, the freesurfer parcellation atlas (which for example specifies the probability of precentral gyrus at a particular location) is not symmetric, thus it will treat the left and right hemispheres of your subject differently if you flipped it.
--Thomas
On Sun, Jun 17, 2012 at 10:04 PM, Bruce Fischl fischl@nmr.mgh.harvard.edu wrote:
Hi Remmelt
folding patterns are not symmetric across the hemispheres, so the cortical parcellation will change if you flip things left/right, which is appropriate. I would be surprised if you see much change in the thickness though.
cheers Bruce
On Fri, 15 Jun 2012, Schur, Remmelt R. wrote:
Dear Freesurfers,
Grey matter volumes of the same structure seem to be measured differently
depending on if FreeSurfer establishes it as in the left or in the right hemisphere. For example, if I take a look at the caudal anterior cingulate in the right hemisphere and I flip the image (creating a mirror image of the same hemisphere, which will then be treated by FreeSurfer as a left hemisphere), the same structure has a totally different grey matter volume (see attachment, on the right the original and on the left the flipped version). Does anybody know what's the logic behind this and what's the best way to avoid FreeSurfer creating asymmetry between left and right hemisphere (maybe averaging flipped and non-flipped data?)
Thanks!
Kind regards, Remmelt Schür
IMPORTANT WARNING: This email (and any attachments) is only intended for the use of the person or entity to which it is addressed, and may contain information that is privileged and confidential. You, the recipient, are obligated to maintain it in a safe, secure and confidential manner. Unauthorized redisclosure or failure to maintain confidentiality may subject you to federal and state penalties. If you are not the intended recipient, please immediately notify us by return email, and delete this message from your computer.
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Bruce Fischl -
Schur, Remmelt R. -
Thomas Yeo