Neuromag data processing

[Robert Oostenveld]

Hi Arno

On 21 Feb 2007, at 13:57, arno wrote:
> Is it possible to do source localization of Neuromag data using
> Fieldtrip? I looked at the documentation but did not find anything.
> How can I read the BEM model within Fieldtrip and use it. Just a
> few commands to start up would be useful.

Yes, that is possible. You can either use headmodels (single sphere,
multi-sphere, or realistic single-shell) that are constructed within
FieldTrip, but you can also use the neuromag mex files in combination
with headmodels that were constructed in the Neuromag software.

Since I do not have the complete neuomag software, I cannot explain
in detail how to follow the second "neuromag" path: I did write part
of the code for it, and included other parts contributed by Joachim
Gross and Lauri Parkkonen, but I cannot easily test it myself or make
a demo script.

The first path (i.e. using "pure fieldtrip") is of course fully
accessible to anyone. Note that although we at the Donders sometimes
use the CTF software to construct headmodels, that is not a
requirement as you can do it completely within FieldTrip. An example
for the different MEG headmodels is given on
http://www2.ru.nl/fcdonders/fieldtrip/doku.php?
id=fieldtrip:documentation:make_leadfields_using_different_headmodels
I suggest that you start with the simplest one, a manually specified
single-sphere model
   cfg.vol.r = 12;       % radius, here in cm
   cfg.vol.r = [0 0 4];  % origin, here in cm
The preferred headmodel is a single-shell model (based on an
algorithm and code from Guido Nolte) which is the las one on the
example page, see the PREPARE_SINGLESHELL function for that. Note
that the headmodel, the anatomical MRI (for plotting and headmodel
construction), the sensors and the dipoles all should be expressed in
the same (head-)coordinate system.

best regards,
Robert