[FieldTrip] Standard BEM or FEM models for use with 256-electrode EEG data recorded with EGI caps

[Cristiano Micheli]

Dear Laith,

this might be possible if you have the subject-specific MRI by following
the tutorial here:
http://www.fieldtriptoolbox.org/tutorial/headmodel_eeg_bem

and using the function ft_prepare_mesh and the tutorial command:

cfg=[];
cfg.tissue={'brain','skull','scalp'};
cfg.numvertices = [3000 2000 1000];
bnd=ft_prepare_mesh(cfg,segmentedmri);


which uses the segmented MRI (see tutorial). The bnd(3) variable should
contain your triangulated surface with 1000 vertices. Let me know if that
works. Of course you should see the skin and the neck in the original MRI.

If you do not have an anatomical MRI that extends down to the chin you
could try with a template, such as this:
ftp://ftp.fieldtriptoolbox.org/pub/fieldtrip/tutorial/beamformer_extended/subjectK.mri
and the corresponding segmented version
ftp://ftp.fieldtriptoolbox.org/pub/fieldtrip/tutorial/beamformer_extended/segmentedmri.mat

This goes down to the chin. Then you take care of rearranging the position
of the EEG electrodes according to this:

http://www.fieldtriptoolbox.org/example/align_eeg_electrode_positions_to_bem_headmodel

I hope this helped
Cris




On Tue, Jan 19, 2016 at 5:41 PM, Laith Hamid <lah at pedneuro.uni-kiel.de>
wrote:

> Dear Cris,
>
> thank you very much for your answer. I am refering to an issue that was
> discussed in this thread from April 2013:
>
>
> [FieldTrip] source analysis EEG data without MRI
>
>
> The thread however does not offer a segmentation or head model for
> download. Some electrodes in the EGI 256-electrodes cap are placed on the
> cheeks or on the back of the neck and these areas are not modeled by the
> standard BEM skin compartment in the standard BEM model. My question was
> about a standard segmentation that extends the skin (and skull) compartment
> downwards to allow these electrodes to sit on the nodes of the skin mesh.
>
> Best,
> Laith
>
>
>
>
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