[FieldTrip] electrode positions of 4D data

[Gopakumar Venugopalan]

Greetings, the location file for 4D is in the form of an .xyz file. This is
not the same as a head shape file--though both use the x, y, and z, and are
conceptually related. The head shape file is unique to inviduals, when the
location file will tell you the exact position, in Cartesian space,  and
orientation of the electrodes. Many researchers on the this list, and on
others have locations files for a 248 channel 4D system.  Though they are
standard, even those can vary very slightly from machine to machine and day
to day.
If you export your data from the MSI system it will put out three files, one
of which is an .xyz file, which is your location file.
If you have EEGLAB or Fieldtrip you should look for the.xyz file.

All the best.



2011/7/4 Schönherr, Margit <Margit.Schoenherr at uk-erlangen.de>

> Hello Yuval,
>
> thank you, giving the electrode labels {'E1', ..., 'En'} reads in the EEG
> data only (without MEG). But still, I have no electrode positions.
>
> Julian, yes, we have digitized the electrodes, but unfortunately I cannot
> distinguish the electrode positions in the list of 3000 head shape
> digitization points. So, this does not solve the problem.
>
> Margit
>
>
> ________________________________________
> Von: fieldtrip-bounces at donders.ru.nl [fieldtrip-bounces at donders.ru.nl] im
> Auftrag von Yuval Harpaz [yuvharpaz at gmail.com]
> Gesendet: Freitag, 1. Juli 2011 17:12
> An: Email discussion list for the FieldTrip project
> Betreff: Re: [FieldTrip] electrode positions of 4D data
>
> Dear Margit
> with a previous version of fieldtrip I found that not only the location of
> the electrodes was not in the data structure but also the EEG data. this is
> when specifying channel = 'EEG'; giving it the channel labels solved it-
> {'E1' E2' ... 'En'}; if I remember well the elec position was read then. if
> worse comes to worst you can try reading the EEG location with msi >>
> matlab<http://biomag.wikidot.com/msi-matlab> tool. I assume the electrodes
> were digitized.
> yuval
>
> 2011/7/1 Schönherr, Margit <Margit.Schoenherr at uk-erlangen.de<mailto:
> Margit.Schoenherr at uk-erlangen.de>>
> Hello,
>
> we are using a 4D Neuroimaging device with 248 magnetometers. When reading
> combined MEG and EEG data sets, there is no elec data structure which would
> contain information about the electrode positions,labels... At line 161, the
> ft_read_header function calls
>
> hdr.grad = bti2grad(orig);
>
> which only returns the grad structure, whereas for Neuromag data at line
> 1056
>
> [hdr.grad, elec] = mne2grad(orig);
>
> has 2 outputs.
>
> There doesn't seem to be anything implemented for getting the electrode
> positions, is there? I am using fieldtrip-20110603. Is anyone currently
> working on this, or has already solved the problem?
>
> Thank you,
> Margit
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>
>
>
> --
> sent from my 4-year-old PC. poor fellow, only ipod classic, no mail there.
>
> Y.Harpaz
>
> a link to the BIU MEG lab:
> http://faculty.biu.ac.il/~goldsa/index.html<
> http://faculty.biu.ac.il/%7Egoldsa/index.html<http://faculty.biu.ac.il/~goldsa/index.html>
> >
>
> "Many were increasingly of the opinion that they'd all made a big mistake
> in coming down from the trees in the first place. And some said that even
> the trees had been a bad move, and that no one should ever have left the
> oceans". Douglas Adams
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