Freesurfer May 2010

freesurfer@nmr.mgh.harvard.edu

98 participants
145 discussions

Incorporating T2 and T1 images in recon-all
by Dan Dillon 03 May '10

03 May '10

Dear FreeSurfers, I have 2 identical structural scans for my subjects: one is T1-weighted and the other is T2-weighted. Is it possible to pass both scans to recon-all? The T1-scans are rapidly acquired MEMPRAGEs, and recon-all seems to be having some difficulty distinguishing cortex from dura around the sagittal sinus. I thought adding the T2-weighted scan into the mix might improve things a bit. Can this be done, and if so, how? Thanks! Dan Dillon, Ph.D. Post-doctoral Fellow Affective Neuroscience Lab Dept. of Psychology, Harvard University Phone: (617) 495-1889 E-mail: <mailto:dillon@wjh.harvard.edu> dillon(a)wjh.harvard.edu

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Re: [Freesurfer] Vertices to matrix coordinates
by f.leone＠donders.ru.nl 03 May '10

03 May '10

Dear Doug, Thanks a lot for the fast reply. I got it to work with your tips. The missing link for me was especially that I could get the vertices locations by using read_surf over the mgz file. Instead of the fmri_info rotation matrix I can also use the matrix from the nii-file, can't I? They are almost exactly equal. Now I got the tal coordinates and try to convert them to indices in my nii matrix. I now do that by add the origin of the nii scan to the found tal coordinates (converted to mni or not). But this makes the brain end up too high in the figure. Any idea how this can be? This is true irrespective of the rotation matrix I take. Thanks a lot in advance, it looks really promising, kind regards, Frank ----- Original Message ----- From: "Douglas N Greve" <greve(a)nmr.mgh.harvard.edu> To: "Frank Leoné" <f.leone(a)donders.ru.nl> Cc: freesurfer(a)nmr.mgh.harvard.edu Sent: Monday, May 3, 2010 5:55:33 PM GMT +01:00 Amsterdam / Berlin / Bern / Rome / Stockholm / Vienna Subject: Re: [Freesurfer] Vertices to matrix coordinates The coordinate system is not easy to explain in an email. There are power point slides on our wiki about the geometry used. To get from surface xyz to column, row, slice in the orig.mgz, first get a matrix from the orig.mgz with mri_info --tkrvox2ras orig.mgz this will be 4x4, multiply the inverse of this matrix by the surface xyz (adding a one to make it 4x1) to get the col, row, slice in the orig. doug f.leone(a)donders.ru.nl wrote: > Hi all, > > I checked quite a number of previous posts, but still can't seem to figure out what the vertices numbers given by read_annotation in matlab stand for. My questions are: > > - In what reference frame are they? > - How do I convert them to coordinates in my original structural image (an x * y * z matrix, based on a nii-file)? > > Thanks a lot in advance! > > kind regards, > > Frank > > > -- Douglas N. Greve, Ph.D. MGH-NMR Center greve(a)nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: www.nmr.mgh.harvard.edu/facility/filedrop/index.html -- Frank T.M. Leoné, MSc Graduate student | Donders Institute for Brain, Cognition and Behaviour f.leone(a)donders.ru.nl | +31 24 36 12542 / +31 24 36 68388 | Room B.1.31 / Room 1.34

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Vertices to matrix coordinates
by f.leone＠donders.ru.nl 03 May '10

03 May '10

Hi all, I checked quite a number of previous posts, but still can't seem to figure out what the vertices numbers given by read_annotation in matlab stand for. My questions are: - In what reference frame are they? - How do I convert them to coordinates in my original structural image (an x * y * z matrix, based on a nii-file)? Thanks a lot in advance! kind regards, Frank -- Frank T.M. Leoné, MSc Graduate student | Donders Institute for Brain, Cognition and Behaviour f.leone(a)donders.ru.nl | +31 24 36 12542 / +31 24 36 68388 | Room B.1.31 / Room 1.34

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orientation of the data
by Janani Dhinakaran 03 May '10

03 May '10

Hello experts, I've been having some trouble with the talairach during recon. I followed previous instructions and checked the rawavg image and found that it was in wrongly oriented. The sagittal picture was appearing under coronal but upsidedown, the coronal picture was sideways in the transverse section and the transverse was in the sagital section. I wonder if there is a place where I can send the data for someone to see and tell me how exaclty to flip the orientation of it to suit FreeSurfer. I would also like to know whether there is a shorter way of processing the data for only mri-stats without running recon-all for all the subjects' data we have. Thank you Jan

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cortical thickness calculation
by miro drahos 30 Apr '10

30 Apr '10

Dear Surferteam, I have been trying to understand details on how the cortical thickness is calculated. I read in the article: "we compute the closest vertex on the pial from each vertex on the white, and vice-versa, then set the thickness to the average of the two." I have tried to carry out this calculation myself, using the generated surfaces lh.white and lh.pial and compare my results to the thickness generated by FS (lh.thickness). There is a one-to-one correspondence between the vertices of the white and pial meshes, which makes it quite straightforward: e.g.: Vertex 100 on white surface has distance from pial surface = 2.5 mm, vertex 100 on pial surface has distance from white surface = 2.6 mm, average == thickness at vertex 100 = 2.55 mm. However, the results that I am getting are different from lh.thickness. I expected discrepancies on the order of rounding errors, but half of the thickness values differ more than 0.001, with some differing as much as 2 mms! What am I missing? Could you please elaborate a bit on how you define the cortical thickness? Thank you very much, Miro Drahos

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Freesurfer May 2010