[Eeglablist] Group analysis with dipole fitting results from custom head model

[Jacobsen,Noelle A]

Hello Everyone,

I am trying to create and use a custom head model for dipole fitting, but having an issue plotting the dipole results. How can I map individual dipole positions to the MNI coordinate system so I can perform group analyses in an EEG STUDY (perhaps by applying a transformation matrix to the dipole positions) ?

Here are the steps I used to create a custom 5-layer FEM head model from a subject MRI using Fieldtrip:
1) MRI normalized to MNI space
2) MRI resliced using ft_volumereslice
3) MRI realigned to the CTF coordinate system by marking fiducials (nas, lhj, rhj; same fiducials used to coregister EEG electrode locations) and using ft_volumerealign
4)MRI segmented and used to create mesh (ft_volumesegment, ft_prepare_mesh)
5) Electrodes co-registered to MRI based on fiducials (nas, lhj, rhj) using ft_electroderealign
6) Created head model and source model (ft_prepare_headmodel, ft_prepare_sourcemodel, ft_prepare_vol_sens)
7) Computed leadfield matrix  (ft_prepare_leadfield)

Dipole fitting:
In my dipfit settings, I selected my headmodel.mat with the transfer matrix computed (output from ft_prepare_vol_sens) for EEG.dipfit.hdmfile, my realigned MRI.nii for EEG.dipfit.mrifile, my coregistered electrode locations for EEG.dipfit.chanfile. I modified pop_multifit to allow for the source model containing leadfield matrix and as optional input because I think pop_multifit was recalculating leadfield for each component, which is unnecessary and time consuming.  I thought Fieldtrip contained a check to avoid re-computing the, but some part of dipfit or fieldstrip doesn't seem to store or check for these variables.

Dipole results:
Currently, the resulting dipoles seem to be localized accurately when plotted on the subject MRI, but do not appear to be oriented correctly when plotted with the template MRI (avg152t1.mat) as the background image.

Software versions:
I'm using Matlab 2018a, EEGlab 2021, dipfit4.1, Fieldtrip-20210601

If you see any flaws with my methodology, please let me know! This is my first time trying to use custom head models.

Thank you,
Noelle Jacobsen
PhD Candidate
Human Neuromechanics Laboratory
University of Florida