[FieldTrip] electrode positions of 4D data

[Schönherr, Margit]

Hello Jan-Mathijs,

thanks a lot, I have 14 user_blocks and I found the points and labels in hdr.orig.user_block_data{1,12}.

Best,
Margit

________________________________________
Von: fieldtrip-bounces at donders.ru.nl [fieldtrip-bounces at donders.ru.nl] im Auftrag von jan-mathijs schoffelen [jan.schoffelen at donders.ru.nl]
Gesendet: Montag, 4. Juli 2011 14:08
An: Email discussion list for the FieldTrip project
Betreff: Re: [FieldTrip] electrode positions of 4D data

Hi Margit,

There should be information with respect to the electrode locations (if digitized indeed) in the header-information.
I don't know about the digitized electrode positions, because at the time that I wrote the code dealing with 4d-data we did not simultaneously collect EEG and MEG data, so there is no way for me to check.
Could you check whether your data.hdr contains the following field: data.hdr.orig.user_block_data?
This should be a cell-array, and in my headers typically the 11th cell contains the info about the digitized electrodes (in my case only information about the 5 coils and landmarks is present). It's called 'b_eeg_elec_locs' (check hdr.orig.user_block_data{x}.hdr.type). The hdr.orig.user_block_data{x}.pnt contains the coordinates of the points. How many are there in your header? If this number > 11 then chances are that these are the electrode positions.
We could of course then easily extend the code in order to spit these out in a more convenient format.

Best wishes,

Jan-Mathijs



On Jul 4, 2011, at 1:37 PM, Schönherr, Margit wrote:

> 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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>
>
> --
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>
> 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>
>
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Dr. J.M. (Jan-Mathijs) Schoffelen
Donders Institute for Brain, Cognition and Behaviour,
Centre for Cognitive Neuroimaging,
Radboud University Nijmegen, The Netherlands
J.Schoffelen at donders.ru.nl
Telephone: 0031-24-3614793


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