[FieldTrip] CTF275 MEG channel position from FieldTrip to EEGLAB

[Zhi Li]

Hi Arno,

Many thanks for your kind suggestions. You are right about the difference
between EEG and MEG data and IClabel is modelled with EEG data. But I found
that the eye components of most of our MEG dataset can be
correctly labelled by IClabel. I did not use the components labelled by
IClabel directly, instead I just use IClabel to narrow the search for
artifactual components in our MEG dataset with hundreds of subjects that
each one completed several tasks. I ranked the score by IClabel and found
most artefact components were in the top 3 components. In my preprocessing
pipeline, I manually find and check the artifactual components in the top 3
components labeled by IClabel or top 10 if the artefact components were not
in the top 3. I found this strategy is working for all of our dataset.

About the data transformation between Fieldtrip and EEGLAB, I solved this
one by adding the channel type of CTF275 to *pop_fileio*.

Thanks and best,

Zhi Li

On Mon, 11 Jul 2022 at 17:49, Arnaud Delorme via fieldtrip <
fieldtrip at science.ru.nl> wrote:

> Hi Zhi Li,
>
> You cannot use IClabel to detect ICA artifactual components because MEG
> components will be different than EEG components, and IClabel has been
> trained with EEG components. You would need a version of ICLabel that is
> trained with MEG components (there is no such version to my knowledge).
> This page describes how to go back and forth between Fieldtrip and EEGLAB
> https://eeglab.org/others/EEGLAB_and_Fieldtrip.html
>
> Cheers,
>
> Arno
>
>
> > On Jul 6, 2022, at 2:27 PM, Zhi Li via fieldtrip <
> fieldtrip at science.ru.nl> wrote:
> >
> > Hi Jan-Mathijs,
> >
> > Many thanks for your kind reply. I have solved this problem by adding
> the ctf275 channel type to the source code for data reading. I'd like to
> use IClabel which is a plugin of EEGLAB to label the components
> automatically.
> >
> > Best wishes,
> >
> > Zhi Li
> >
> > On Wed, 6 Jul 2022 at 12:01, Schoffelen, J.M. (Jan Mathijs) via
> fieldtrip <fieldtrip at science.ru.nl> wrote:
> > Hi Zhi Li,
> >
> > I am unfamiliar with the way in which EEGLAB deals with sensor/electrode
> positions, and how these are read from the data file.
> >
> > On the other hand it is unclear to me what your actual problem is. Is it
> only a matter of visualization (because for ICA the sensor positions are
> not needed)? Have you checked the EEGLAB documentation?
> >
> > Since you are asking for another solution: you can also do the ICA in
> fieldtrip, there’s no need to go to eeglab for that.
> >
> > Best wishes,
> > Jan-Mathijs
> >
> >
> >> On 30 Jun 2022, at 22:07, Zhi Li via fieldtrip <fieldtrip at science.ru.nl>
> wrote:
> >>
> >> Hi,
> >>
> >> I would like to use ICA and IClabel in EEGLAB to detect artefacts in my
> MEG data. But no matter if I used fieldtrip2eeglab or pop_fileio, the
> gradiometer channel positions cannot be correctly extracted from the ctf275
> .ds folder. The channel positions in eeglab format EEG are all empty.
> >>
> >> I tried to copy the channel information directly from the header of the
> ctf275 data folder but the MEG channels cannot be projected on the 2-D map
> appropriately. It seems like the channel position in the MEG data imported
> by FieldTrip are the real locations of the MEG helmet and their unit is cm.
> whereas the channel position in EEGLAB is based on the 10-10 system which
> is already on the scalp. Hence the projected channels on the scalp are all
> misplaced if I use the raw XYZ from the header of ctf275 data.
> >>
> >> May I ask how I could transform the MEG channel position from FieldTrip
> to EEGLAB appropriately, or is there any other solution? Many thanks.
> >>
> >> Best regards,
> >>
> >> Zhi Li
> >> _______________________________________________
> >> fieldtrip mailing list
> >> https://mailman.science.ru.nl/mailman/listinfo/fieldtrip
> >>
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