Hi Jee Won and Priyanka, there are several things going on here. First,
the original aseg (aseg.presurf.mgz) has these areas labeled as nothing
(0); they show up as WM in aseg.mgz and aparc+aseg.mgz. Obviously, it
would be good to have them properly labeled, but is this critical to
your applications? Eg, are you looking at ventricular volume?
On 12/21/2021 9:19 AM, Kang, Jee Won wrote:
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Hello all,
I found a very common error in our data while I was correcting recons.
The lateral ventricles (usually the horns) are being misclassified as
white matter in aseg.mgz. This happened in around 1/3 of our 108
subjects.
We were able to fix this issue by manually filling in the ventricles
in aseg.presurf.mgz and re-running Freesurfer with the command
autorecon2-noaseg -autorecon3, but this is obviously quite a
labor-intensive fix for a substantial portion of our data. This was
also the only way to fix the segmentation - filling in the mislabeled
areas as 255 in the wm.mgz did not fix the problem. I'm not sure why
Freesurfer is having issues here, as the areas it is mislabeling have
very distinct intensity boundaries - the T1 intensity is usually
between 20 and 45 in the areas that are being mislabeled. I've
attached a screenshot of a subject's aseg.presurf.mgz who had this
ventricle segmentation issue, and you can see that a large portion of
the right ventricle has just not been segmented properly;
the intensity of the area in the aseg.presurf.mgz and wm.mgz volumes
is just 0, and it was 41 (R cerebral white matter) in aseg.mgz.
Would you be able to provide some insight into why this might have
been happening, and what we could do in the future to prevent such
extensive manual editing in the future? I can also say that this data
was processed with a T2 image as well, and supplying that flag didn't
help with the segmentation issue.
Thank you,
Jee Won
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