[FieldTrip] BEM for MEG data

[Joram van Driel]

Dear Fieldtrip users and developers,

I've been struggling quite some time now with the following problem.

We want to do source localization of MEG data from an experiment with 10
subjects. We collected MRIs using a Phillips scanner (UvA), and MEG data
using the Neuromag Elekta scanner (VUmc).

Using Neuromag software in Linux (seglab, xfit), I've created BEM forward
models based on coregistered MRIs (coregistration also done using the
Neuromag package), which result in .fif files (extension *bem-sol.fif).

Using these models we want to continue computing the leadfields and doing
source reconstruction in Matlab. For the latter, we have our own customized
codes; to get the leadfield, we need some step in between. I'm trying to
use fieldtrip functions for this but I get stuck. Here's what I do:

- Import the bem fif files using the mne toolbox (function:
mne_read_bem_surfaces).
- Attach the imported boundary data to a vol structure as follows:

[bem] = mne_read_bem_surfaces(bemfilz(subno).name);
vol                 = [];
vol.bnd.pnt         = bem.rr;
vol.bnd.tri         = double(bem.tris);
vol.unit            = 'mm';
vol.cfg.sourceunits = 'mm';
vol.type            = 'bemcp';
vol.cfg.numvertices = bem.np;

- Import the sensor locations using ft_read_sens and convert to mm using
ft_convert_units.
- Check whether the resulting structures are OK for leadfield computation
using ft_prepare_vol_sens. This results in an error "Unsupported volume
conductor model for MEG".

I also tried ft_read_vol, but for Neuromag this needs the meg-pd toolbox
which doesn't run on Windows (the Linux we use for the Neuromag software,
in turn, is a virtual machine and doesn't have Matlab).

Is there a way around this? Using BEM models for MEG data should in
principle be possible, but not using Fieldtrip?

Any suggestions would be much appreciated!
Thanks in advance,

Joram


-- 
Joram van Driel, MSc.
PhD student at the University of Amsterdam
Department of Psychology, Brain & Cognition
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