[FieldTrip] BESA vs. Fieldtrip dipole fit

[Vladimir Litvak]

Hi Robert and everyone,

We are fitting dipoles to some epileptic spikes in MEG and we are trying to
do them initially in BESA and then reproduce the same result in FT because
we only have an old version of BESA where we cannot integrate individual
anatomy.

The problem is that in 80% of the cases the dipole goes to a different
place in FT for the same time window even if we disable the grid search and
initialise with the Talairach coordinates from the BESA fit. I thought that
was because FT fits a single topography whereas BESA fits a whole segment
but looking at the code it seems that FT does something quite similar to
BESA so this is not the reason. Do you have any ideas how we can harmonise
the two? Perhaps it's a matter of regularisation/pre-whitening? The data
are MaxFiltered Neuromag mags.

Thanks,

Vladimir
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