[FieldTrip] Computing the system matrix in a the forward model?

patrick cox phc5 at georgetown.edu
Tue Feb 7 05:56:09 CET 2012


I have just started using feildtrip, and I am trying to do some source
localization using beamforming. I am working with EEG data and would like
to anatomically constrain the forward model, so I am trying out the various
BEM methods in fieldtrip. As a first pass I have been using the SPM T1
template, but I also have anatomical scans of my subjects.

My problem is that when I try to calculate the model for the volume
conductor using most of the methods (openmeeg, dipoli), my vol structure
does not contain a vol.mat field (which I believe is the system matrix).
The one BEM method that actully returns a vol with a system matrix is the
BEMCP method, but the vol.mat file is all NaNs! I have tracked the problem
to the calculation of the Cij's, particularly C12 and C21, in the
ft_headmodel_bemcp.m which contain a large number of NaN entries.

Does anyone have a fix for this, or a advice on how to producing vol
structures with system matrices/vol.mat fields using the other BEM methods?

Patrick Cox
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