Importing EEG positions (intra-cranial EEG)

Bugs
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1

Hello François,

I have a trouble to load in Braintorm the coordinates xyz that localize intra-cranial electrodes. My set of electrodes contains sEEG and ECOG contacts. The file I am trying to load is a .els from Cartool. The error I got is attached to this message. Could you please explain me how should be organized the coordinates to have a valid format for Brainstorm?

Thanks,

Sophie

2

Hi Sophie,
Can you post your .els file here or send it to me by email?
Thanks
Francois

3

There was a few errors in the .els reader.
It’s fixed, you can update Brainstorm and try again.
Is it normal that your contact b4 is called “b 4” ?
Also, the type of the group “Grille” could be 2 (ECOG) instead of 3 (EEG).

Regarding the registration with the head, you need to add some references to this file if you want it to be registered automatically.
The easier would be for you to save the positions of the MRI fiducials NAS/LPA/RPA in the .els file, in the same coordinate system as the SEEG/ECOG contacts.

You’d have to edit accordingly the header of the file:

  • line #2: total number of electrodes (add 3)
  • line #3: number of groups of electrodes (add 1)
  • Add a group “Fiducials” (type 3=EEG, 3 channels)
  • Rest of the file unchanged (except for the type of group Grille)
ES01
85
5
Fiducials
3
3
X Y Z NAS
X Y Z LPA
X Y Z RPA
Grille
64
2
...

Does it work?
Francois

4

Hi François,

thank you for the corrections. I understood the errors you highlight in the .eps file. I can now download the .els file. But, the electrodes are still far from the brain. Do you have any idea why are the electrodes localized outside the cortex?
I attached to this email the dysplay sensors from Brainstorm (.png) and the .els file I downloaded to reach that display.

Thanks for your advice,

Sophie

5

You need to add the get the position of th NAS/LPA/RPA in the same coordinate system as the electrodes.
In the program with which you created the .els file, select the same MRI slices as the ones used in the MRI viewer in Brainstorm. Write down the coordinates for the three fiducials, add them to the .els file as indicated before.
If the final alignment is not correct, it’s because the coordinates of your NAS/LPA/RPA are not in the same coordinate system as the contacts.

6

Yes, you got it right. It works now.

Many thanks !

7

FYI: We improved significantly the tools available in Brainstorm for processing and visualizing SEEG and ECOG data, including new options for volume coregistration. They are now documented in a new tutorial:
http://neuroimage.usc.edu/brainstorm/Tutorials/Epileptogenicity