[FieldTrip] Please help me get component dipole fitting results using custom anatomy into normalized template for EEGLAB clustering.
chadwick.boulay at gmail.com
Mon May 6 07:36:18 CEST 2013
Dear Fieldtrip users,
Using the subject's MRI and recorded EEG electrode locations, I've
managed to segment the MRI, create the volume conduction model, align
the electrodes, create a sourcemodel using a grid warped from the MNI
template, create the leadfield, and perform ft_dipolefitting on IC
weights (imported from EEGLAB). The geometry, electrode positions, and
mri all line up (coordsys='ctf', unit='cm') and the calculated dipole
positions are what I would expect.
[Aside: All of my topoplots have the electrodes positioned correctly
relative to each other but the nose and ears are 90 degrees from where I
would expect them. Do the topoplot functions not know how to deal with
How can I normalize these dipole locations into the template brain so
that I may perform component clustering in EEGLAB?
I have some ideas but I don't know how to implement them.
1) Calculate the transformation matrix to normalize the original MRI to
the template MRI, then apply that transformation to the dipole positions
and momentums. I'm guessing I need to use mri_norm =
ft_volumenormalize(cfg, mri); but then I don't know how to use
mri_norm.transform and mri_norm.initial. Further, the output of
ft_dipolefitting doesn't seem to be suitable for ft_transform_geometry.
2) Since the sourcemodel grid is warped from the template brain, I can
find the sourcemodel grid index closest to the dipole location then set
the new dipole location to be the location of the template grid at the
same index. I don't know how to do this for the momentum but I probably
don't need the momentum for clustering.
3) Start over from the beginning, normalizing the MRI and the electrode
locations as soon as possible then performing all subsequent
calculations using the normalized geometry.
I searched the documentation and the list archives but I could not find
an answer. I am surprised because I expected dipole normalisation to be
a common requirement. Maybe I am missing something simple.
Thank you in advance for any help.
JSPS Postdoctoral Fellow
boulay at brain.bio.keio.ac.jp
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