EEG forward modelling using BEM

[Robert Oostenveld]

Hi Fabio

On the ftp server you can find a file standard_BEM.zip which contains
a precomputed BEM model that you can use. The geometry is based on the
collin27 brain, and I believe it also includes the collin27 MRI. I.e.,
it is aligned with MNI152, but uses a crisp MRI and not the fuzzy
MNI152, because from the latter one you cannot get a reasonable
estimate of the skull geometry.

The mesh vertex coordinates are expressed in MNI coordinates (in mm).
You should carefully align your electrodes with the skin surface, i.e.
plotting the mesh and electrodes in one figure should give a
meaningfull figure.

Have a look at the electroderealign function and at http://fieldtrip.fcdonders.nl/example
. Also look at the fieldtrip/plotting/plot_mesh and plot_sens
functions, which will be usefull for the realignment of your
electrodes with the model skin.

Hope this helps to get you started.
Robert


On 15 Sep 2009, at 23:41, Fabio Meneghini wrote:

> Hi to all,
> Please help me, it took me a lot of trials and troubles to avoid
> annoying people with (possibly) trivial issues....but eventually I
> don't know what else remains to try...
> I'm new using FieldTrip, and I'm mainly interested in computing the
> EEG forward model on a standard MNI head model  (MNI152, the one you
> can find in FSL software package), using BEM algorithm on 3, or better
> 4 surfaces.
> First of all: has anyone ever done this before? If so, this might save
> me a lot of hard times...
>
> I read the the tutorial about building BEM meshes models, but let's
> suppose I already have my model segmentation image (182x217x182
> voxels, filled with integers numbers). Can I start from that, ignoring
> the original MRI images?
>
> I got my eeg channels coordinates. Are they supposed to be expressed
> in mm, rather than meters? What is the origin of the coordinates
> intended to be? And what about the conductivities of the various
> compartments? where can I set them?
>
> Waiting for some light in the dark, thank you for your attention.
>
> best,
>
> Fabio Meneghini
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users
> of the FieldTrip  toolbox, to share experiences and to discuss new
> ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html
>  and http://www.ru.nl/neuroimaging/fieldtrip.
>

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.