Going from 10-20 system to egi nets in infants

Discussions
1

Hi Francois,

With François Leroy and a phD student, we are studying over which infant’s brain area (using MRI) EEG electrodes are, as the relation between brain and external anatomical markers might be different in infants.

We have located 19 electrodes in a set of 16 babies, based upon the internationally standardized 10-20 system (http://www.bem.fi/book/13/13.htm). We have virtually located the electrodes on the baby’s head using external referent as we would have done with a real baby, using Brainvisa and python
Do you see an easy way to import the channel location in BST as for the moment they are in a nifti or brainvisa format?

We would also like to have a localization for a whole Egi net. Do you see how we can use the known locations of the 19 electrodes plus the anatomical references (inion, nasion, and pre ears markers) to constraint the location of the other electrodes of the EGI net?

Thank you for every piece of advice,
See you,

2

Hi Ghislaine,

Do you see an easy way to import the channel location in BST as for the moment they are in a nifti or brainvisa format?

You can import any ASCII file (one line = one electrode) as a channel file in Brainstorm. Right-click on a subject or condition > Import channel file. Just pick the appropriate file filter (probably "ASCII: Name,X,Y,Z" or "ASCII: X,Y,Z").

All the positions must be in Brainstorm/SCS/CTF coordinates. Read the following page for instructions on how to convert from MRI coordinates to SCS: http://neuroimage.usc.edu/brainstorm/CoordinateSystems

We would also like to have a localization for a whole Egi net. Do you see how we can use the known locations of the 19 electrodes plus the anatomical references (inion, nasion, and pre ears markers) to constraint the location of the other electrodes of the EGI net?

I don't have functions to do this. The closer would be the warping of a default anatomy to an individual one using some head points: http://neuroimage.usc.edu/brainstorm/Tutorials/TutWarping
If you define your 10-20 as the "head points" and the full EGI cap as a "surface". But I think it will be faster for you to do the interpolation by yourself. It's not a very complicated problem: 1) Convert everything in spherical coordinates and 2) interpolate the EGI electrodes radii using your 10-20 radii. There are tens of ways to do that in Matlab, Francois Leroy will know how to do this.

Cheers,
Francois