Hi Alex,
the manual editing can certainly effect the final surface placement. Mostly if a large piece of wm is missed, or sometimes we edit the brain volume directly to remove some dura that gets kept within the pial surface.
The qsphere is used to guide the topology correction, but itself is not corrected, so it won't have an Euler # of 2. You can't run mris_euler_number on thickness, since it's not a surface (but a scalar field over the surface). You can run it on the ?h.white and ?h.pial surfaces if you want.
There is actually a means for manual intervention in the spherical morph, but it's rarely needed.
cheers, Bruce
On Mon, 9 May 2005, Fornito, Alexander wrote:
Hi Evelina, Let's see if I understand you... The pial and white boundaries are calculated on the intensity normalized/motion/corrected/averaged image, irrespective of manual editing. Then the manual editing is only done to obtain a surface representation that is visually accurate for display of inflated and/or flattened surfaces, but has not effect whatsoever on the surface estimation used for thickness and curvature calculations? How about inter-subject registration? Is it affected by manual editing? I've been having problems with my surfaces and am trying to work out what's going wrong. My euler numbers are 2 for the white and pial surfaces, but I get the following message when I comupte it for the qsphere (for one rh.qsphere case):
euler # = v-e+f = 2g-2: 156076 - 468733 + 312496 = -161 --> 81 holes F =2V-4: 312496 != 312152-4 (-348) 2E=3F: 937466 != 937488 (-22)
total defect index = 185
Also, I get a "segmentation fault" when I run mris_anatomical_stats rh thickness for this same person.Visually, I've noticed that the pial and wm surfaces intersects on some parts of the brain? Could this be the problem? Than ks again for your help, Alex
-----Original Message----- From: Evelina Busa [mailto:[EMAIL PROTECTED] Sent: Sat 5/7/2005 6:51 AM To: Fornito, Alexander Cc: Subject: RE: [Freesurfer] Manual editing tips?
Hi Alex,
The normalized brain volume is created quite early on in the process -- first the raw data are converted from their native scanner format, then motion corrected into what we call the 'orig' volume, then the intensities are normalised to what we call the T1 volume, then the non-brain tissues are stripped from the T1 and we have the 'brain' volume.
The WM volume is then segmented out of the brain volume, and that's what is edited, for the purpose of getting the surface topologically correct. So, although it's mostly true that the brain volume is what is used to calculate the pial/white boundary and cortical thicknesses (thus arbitrary edits to the WM volume won't change that), if the initial surface (which is defined by the wm edits) is far enough off, it won't find the correct location during the final surface deformation.
In other words, it's important that the wm edits be accurate, but rest assured that your edits are not what Freesurfer ultimately uses to determine the cortical surfaces.
This should be welcomed as good news! ;)
Good luck!
On Thu, 5 May 2005, Fornito, Alexander wrote:
Hi once again, Just wanted to also clarify your response: "The surfaces are generated using the normalized brain volume and not strictly the segmented white matter volume, so edits on the WM volume do not arbitrarily affect the cortical thickness measures." This has me a bit confused. What exactly is the normalized brain volume (ie., created at which step/which file name?), and if edits on the WM volume don't affect thickness (and presumably therefore, surface estimation) why do we edit them at all? There's something I a missing, and I'd greatly appreciate it if you could point me in the right direction!! Thanks again, Alex
-----Original Message----- From: Evelina Busa [mailto:[EMAIL PROTECTED] Sent: Thu 5/5/2005 4:23 AM To: Fornito, Alexander Cc: Subject: RE: [Freesurfer] Manual editing tips?
Hi again,
The posterior portion connects to calcarine which makes the big defect. The tutorial pictures and instructions for filling in the posterior ventricles may give the impression that *any* apparent "hole" in the WM volume will necessarily result in a topological defect, but that's not true. It depends on whether that hole when looked at in 3D will still be a hole. This is kind of hard to gauge when going through the slices but the inflated surface tells the story.
Good luck and sorry for my delayed response!
On Wed, 4 May 2005, Fornito, Alexander wrote:
Thanks for your comprehensive response! Very helpful! Just wanted to clarify, why is it that the posterior portion of the lateral ventricles, and not the anterior portions, result in topological defects, if both appear as 'islands' inside the white matter? Thanks again, Alex
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Wed 5/4/2005 2:06 PM To: Fornito, Alexander Cc: freesurfer@nmr.mgh.harvard.edu Subject: Re: [Freesurfer] Manual editing tips?
Hello Alex,
A helpful approach when editing the lateral ventricles is to view the sagittal plane; usually the filling should not extend anterior to the point where the posterior fornix is erased. The axial plane is also useful. The tutorial focuses on the coronal plane, which isn't optimal for determining when to stop the edits (moving anteriorly).
Smoothness of the surface -- the aim of manual editing is chiefly to eliminate the defects that the subsequent automated topology fixer cannot likely handle, whether or not they are easily visible on the surface. The large defects outlined in the manual are pretty safe bets for editing in this respect, and there are other anatomical idiosyncrasies that you'll find in normal or other populations which you can anticipate having to edit in order to "force" a topologically correct surface, e.g. brain lesions resulting in large gaps of white matter voxels.
It's hard to predict what will need to be edited without having done quite a few brains, but in general your choice is to either: a) err on the side of caution and edit whatever corresponds with a visible defect on the inflated surface, or; b) run the topology fixer first to see how/whether it could handle the remaining visible defects, with the risk that you might need to edit the extra defects afterward, anyway. And of course the Euler number calculation can give you precise information about a hemisphere's topological defect index. I'd recommend routinely editing the standard areas that lead to topological defects (as per the tutorial), then running the automated topology fixer, unless it is a structurally unusual brain with quite large visible defects. The automated topology fixer by and large works, and it's usually a better use of operator time to wait on this 5-hour process rather than spend an hour or so, perhaps pointlesssly, doing extra edits first.
The surfaces are generated using the normalized brain volume and not strictly the segmented white matter volume, so edits on the WM volume do not arbitrarily affect the cortical thickness measures.
Hope this helps, if not, ask more -
Hi all, I've noticed that the tutorial's instructions for manual editing ofthe ventricles stops at about slice 92 (for Bert's data). Does this mean only the posterior portion of the lateral ventricles need to be filled, and that there is no need to continue to fill in the ventricles up to the anterior horns as well?Also, a couple more queries re: manual editing: - Sometimes I can see handles emanating from the surface that are notin the areas listed in the manual. Are there any guidelines re: what should be deleted as opposed to what should be filled?- Are there any guidelines for just how smooth the brain surfaceshould be before moving on to create the final surface? Some of my surfaces appear quite smooth (ie., no obvious handles), although somewhat bumpy, esp. around the posterior-dorsal areas.- Am I correct in assuming that what is tissue is edited or not willaffect surface generation and hence estimates of cortical thickness? In this case, is it advisable to carry out some kind of reliability analysis for morphmoteric studies?
Thanks for your help, Alex
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