[FieldTrip] ft_electroderealign

[Konstantinos Tsilimparis]

Hi Sara,

The electrodes and the MRI will be aligned when both are in the same coordinate system that is based on 3 points (the so called fiducials).

You can define the fiducials for your MRI manually using ft_volumerealign with cfg.method = ‘interactive’.

EEG systems typically do not include an integrated way to record and store EEG electrode locations and fiducials. A method to define fiducials and electrode locations is using a 3D scanner and the function ft_electrodeplacement (see: https://www.fieldtriptoolbox.org/tutorial/electrode/#loading-the-data-and-coregistration).

Also, even though I have not used it myself I believe that you can use ft_electroderealign (with the cfg.method of your choice) to realign the electrodes with the head surface (or headshape)  generated from the MRI. In that case you need to take some steps before that, i.e. you need to realign your MRI (ft_volumerealign – which I mentioned in the first paragraph), segment the MRI (ft_volumesegment) and create a head model (ft_prepare_headmodel). The head surface is stored in vol.bnd
(see: https://www.fieldtriptoolbox.org/example/electrodes2bem/)

Best,
Konstantinos

From: fieldtrip <fieldtrip-bounces at science.ru.nl> On Behalf Of Sara Cinelli via fieldtrip
Sent: Monday, July 15, 2024 2:11 PM
To: fieldtrip at science.ru.nl
Cc: Sara Cinelli <sara.cinelli at studenti.unipd.it>
Subject: [FieldTrip] ft_electroderealign

Hello, I'm going to explain my problem regarding the source reconstruction.
How can I realigned the electrode placement with the mesh from the MRI? I tried using the function ft_electrode_realign using the following settings:

cfg = [];
cfg.method = 'interactive';
cfg.headshape = mesh;
elec_realigned = ft_electroderealign(cfg, elec);


My first question is : can I do this having two differents coordinates for the mri and the eeg structure? If not, what sould I do before the realignment? My interest is the have the same coordinates system of the mri image.
Otherwise, the way I explained here is one with the interactive option, how can I understand which transformation to apply (only visually?)?  I saw there could be another option, maybe with the specification of the fiducials from the mri image, but it is not very clear to me how to use it.
Thank you for helping me,

Sara
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20240726/8925b210/attachment.htm>