[FieldTrip] Seeking Guidance on Aligning EGI 128 Electrode Positions with Standard_bem Head Model

[二姬]

Dear FieldTrip Community,

I am Chengyuan Wu from Ningbo Kangning Hospital, reaching out once again in
hopes of gaining insights from this knowledgeable community. Previously, I
discussed my process of source analysis using EEG data collected from the
EGI 128 electrode system and the challenges I faced in aligning electrode
positions with the standard_bem head model in FieldTrip. Despite not having
received a response to my earlier inquiry, I have progressed with the
analysis but have encountered new concerns that I hope to address with your
help.

After manually aligning the EGI 128 electrodes with the standard_bem model
using the 'interactive' method, I proceeded with the source analysis.
However, the source localization results appear unusual, raising doubts
about the reliability of the manual alignment of the EGI electrode
positions. The absence of MRI fiducials such as nas, lpa, and rpa in the
standard_bem, and the provision of fiducial points like FidT9, FidT10, and
FidNz in the EGI electrode file, has left me uncertain about how to
correctly align the electrodes using the 'fiducial' method or any other
more reliable method.

Here is the MATLAB code I used for the manual alignment:

templateheadmodel =
'F:\eeg_ningbo\fieldtrip-20211209\template\headmodel\standard_bem.mat';
load(templateheadmodel);
%% electrode realign as good as possible
cfg = [];
cfg.method = 'interactive';
cfg.elec = elec; %load from the egi128 electrode file
cfg.headshape = vol.bnd(1);
elecR = ft_electroderealign(cfg);


Given these concerns, I am seeking advice on the following:

   1. 1.Are there known issues or limitations with the 'interactive' method
   for aligning electrodes with the standard_bem head model that could lead to
   inaccuracies in source localization?
   2. 2.Can anyone provide guidance or suggest an alternative approach for
   aligning the EGI 128 electrode positions with the standard_bem model,
   especially considering the mismatch in fiducial points between the EGI
   system and the standard_bem?
   3. 3.If anyone has successfully navigated this alignment challenge or
   has insights into using the 'fiducial' method under these circumstances,
   your advice would be invaluable.

Your expertise and suggestions would be greatly appreciated as I strive to
ensure the accuracy and reliability of my source analysis. I am looking
forward to your responses and thank you in advance for your time and
assistance.

Best regards,

Chengyuan Wu Ningbo Kangning Hospital
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