Hi,
I have Talairach coordinates of ECoG electrodes and would like to get for each electrode the closest vertex of my cortex mesh. Context: I would like to use the ECoG signal to seed activity at the corresponding position and forward model that to the scalp level.
Best
Martin
Hi Martin,
What is it more precisely that you don't know how to do?
Francois
When you say "Talairach" it is a real ACcentered coordinates system but still in patient space, or a type of MNI normalization?
If this is a normalized Talaraich system, I'm sorry you're on your own for the transformation Talairach=>MNI, we dropped completely this outdated referential. But importing MNI coordinates in Brainstorm is easy (but not very accurate).
Hi Francois,
I was not sure how to get for a given electrode (in Talairach space) the corresponding vertex of my cortex model.
It is some kind of MNI normalization. I have the Talaraich coordinates of ECoG electrodes projected on a "generic brain derived from MRIs from the McGill Brain Institute".
So, I now took the following approach.

Export the MRI:ICMB152 and the cortex_150002V to matlab.

Extract for all vertices the MNI coordinates (P_mni= cs_convert(myMRI,'scs','mni', Cortex.Vertices);

I multiplied the MNI coordinates by 1000 (I am not quite sure why this is necessary. However, if I do that i get a decent match.

Translate the MNI coordinates to Talairach using this approach http://imaging.mrccbu.cam.ac.uk/imaging/MniTalairach#Approach_2:_a_nonlinear_transform_of_MNI_to_Talairach

Compute for each electrode (in Talaraich coordinates) the distance to all vertices (in Talaraich coordinates)

Find the vertex with the minimal distance to my electrode position.
Best
martin
Looks good. It's a pity you can't simply get the coordinates in native space.
Do you have a MRI or CT scan post implantation for this patient? You could use this to define the positions of the contacts, or at least to check them.
https://neuroimage.usc.edu/brainstorm/Tutorials/ECoG#ECoG_grid:_G
https://neuroimage.usc.edu/brainstorm/Tutorials/Epileptogenicity#Edit_the_contacts_positions
I multiplied the MNI coordinates by 1000 (I am not quite sure why this is necessary. However, if I do that i get a decent match.
In Brainstorm, all the values are saved in international units, so the distances are in meters, while your Talairach coordinates are probably in millimeters.