Electrode positioning (from brainsight file)

Discussions
1

Dear Brainstorm-users,

I am trying to run source analysis on my EEG data but for some reason I cannot import the electrodes at the right position. We have individual MRI data available and electrode locations were saved in a BrainSight neuronav system (coordinate system; Nifti Scanner). I ran a free surfer analysis (recon-all) and read this into Brainstorm. This all seems to work nicely. I have converted the eeg locations using the cs_convert function (cs_convert(sMRI, 'mri', 'SCS', eegcoord_brainsight)) and stored the eeg locations (supposedly in SCS space in a structure named elecinf). Subsequently, I generated a channel_*.mat file that can be imported in Brainstorm.
for i = 1 : numelec
Channel(i).Type = 'EEG';
Channel(i).Name = elecinf.Labels{i};
Channel(i).Loc = elecinf.SCS(i,:)';
Channel(i).Weight = 1;
Channel(i).Orient = [0;0;0];
end

Even though this works, there seems to be still a translation missing in my electrode locations. Attached you can see the an example (Dropbox) . Does anyone know what I missed and how I can improve this?
Much appreciated.
Best, Debby

2

Just to discard that the surface is the one in the wrong position.

Is this cortex properly corresgitered to the MRI?
(Right-click on the cortex, then MRI registration > Check MRI/surface registration)

3

Dear Raymundo, thanks for looking into this. Yes, the coregistration seems to be right (see new screenshot in the dropbox link).

To add a little more information:
I have also read the fiducials from the BrainSight file and this seems to work:
nas_voxel_coords =inv(tmp_sMri.InitTransf{1, 2})*[NAS_BS(1,1:3) 1].';
nas_voxel_coords =round((nas_voxel_coords(1:3)+1)');

in which tmp_sMRI is the free surfer .mgz file and NAS_BS is retrieved from the Brainsight file (so xyz coordinates in Nifti Scanner coordinate system).
Even though this works, I am now overall confused with all the transformation matrices I am afraid. So was it alright to use the InitTransf matrix and load the fiducials like this? Also, trying the same transformation on the electrodes does not work either ...

Many thanks.
-Debby