Aligning head surfces and EEG electrodes

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1

Dear Francois,

I am probably missing something simple, but there is something wrong with the alignment of electrodes and MRI surfaces I have extracted from a T1 image.
Attached is an image showing the electrodes positions over the head at the top right corner (please don’t mind the missing parts at the lower part of the scalp. The T1 image is not of high resolution).

As you can see at the upper left corner, the coordinate system I am using seems to be wrong - e.g. the z axis is pointing down instead of up. I tried playing around with the different function buttons on the edit MRI window, but this did not help.

You can also see the head surfaces are well aligned with the MRI.

Could you please help me see what went wrong?
Thank you very much!

Rachel

2

Hi Rachel,

Where are your electrodes positions coming from?
In most cases, you need to re-align manually the electrodes on the head surface.
The EEG/Epilepsy tutorial illustrates briefly this tool:
http://neuroimage.usc.edu/brainstorm/Tutorials/Epilepsy#Register_electrodes_with_MRI

To ensure a better initial registration EEG-MRI, you can use Brainstorm to digitize the electrodes positions:
http://neuroimage.usc.edu/brainstorm/Tutorials/TutDigitize

Cheers,
Francois

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