Re: [Freesurfer] RAS to MNI coordinates of a label

Which coordinates are you using? Can you send me the label? doug

Yolanda Vives wrote:

Hi Doug,

The problem is that when I put the coordinates in a MNI altas, it says that they correspond to the caudate and not to the cingulate and I would like to know if the procedure that I am following is correct.

Regards, Yolanda

2011/5/3 Douglas N Greve <greve@nmr.mgh.harvard.edu mailto:greve@nmr.mgh.harvard.edu>

Hi Yolanda, they should already be in mni305 coordinates, so the
identity matrix is correct. Did you find a potential problem?
doug

Yolanda Vives wrote:

    Hi all,
     I am interested in obtaining the MNI or talairach coordinates
    of a label. The procedure that I have performed is the following:
     First of all I have performed a QDEC analysis. From the
    results, I have drawn a label of a significant area of the
    brain, that corresponds to the cingulate. Afterwards, I have
    used the matlab function read_label to obtain the RAS
    coordinates of this label. To transform these coordinates into
    mni coordinates, I have read that  if v = [R A S 1]' and X
    matrix is the matrix from talairach.xfm, then vMNI = X*v
     Taking this into account, I have used the X matrix from the
    talairach.xfm of "fsaverage" (where the results of qdec are
    mapped). This matrix is
     1.0 0.0 0.0 0.0
    0.0 1.0 0.0 0.0
    0.0 0.0 1.0 0.0
    so vMNI is the same as v. When I introduce v (or vMNI)
    coordinates into a MNI atlas, I don't obtain the cingulate.

    Could you please help me with this procedure?
     Thank you in advance,
    Yolanda

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-- 
Douglas N. Greve, Ph.D.
MGH-NMR Center
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