Using the previous equation I tried to calculate [tkrR tkrA tkrS] for MNI = [43 -69 47]. Which are ~ MNI coordinates for P4 (electrode 10-20 system)

[43 -69 47 1]/(TalXFM*Norig*inv(Torig))

This resulted in [46.0541 -7.9735 -4.1630]. However, this coordinates in RAS surface space are not even near the place where they were supposed to be, taking into account the projection of P4 to the cortex.

Any ideas about what could be wrong?

Thank you very much,

ines

On Fri, Dec 11, 2015 at 4:20 PM, Inês Violante inesviolante@gmail.com wrote:

Dear Douglas,

I've been looking a that page for a while now and I am very confused...

Are you referring to this example?

2. I have an RAS point on the surface (tkrR tkrA tkrS) ("Vertex RAS"

from tksurfer) and want to compute the MNI305 RAS that corresponds to this point:

MNI305RAS = TalXFM*Norig*inv(Torig)*[tkrR tkrA tkrS 1]'

TalXFM: subject/orig/transforms/talairach.xfm Norig: mri_info --vox2ras orig.mgz Torig: mri_info --vox2ras-tkr orig.mgz

So, is it the case that I just do the equation like this:

[tkrR tkrA tkrS 1]' = [X Y Z (in MNIspace)] / TalXFM*Norig*inv(Torig)

Thank you,

ines

On Fri, Dec 11, 2015 at 4:12 PM, Douglas Greve greve@nmr.mgh.harvard.edu wrote:

...

See if this helps

https://surfer.nmr.mgh.harvard.edu/fswiki/CoordinateSystems

On 12/11/15 10:23 AM, Inês Violante wrote:

...

Dear experts,

I have a set of Talairach coordinates that I want to convert to the individual subject surf RAS coordinates. How can I do this?

Thank you very much.

Ines _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer

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