[FieldTrip] Question on bemcp's and openmeeg's vol.mat

[Lilla.Magyari at mpi.nl]

hi Kidist,

I am wondering if you have installed openmeeg properly. Here is a site to
explain it:
http://fieldtrip.fcdonders.nl/faq/how_can_i_use_openmeeg_for_forward_modelling

Have you followed this?

Lilla



> Hi,
>
> I am working with the combined EEG and MEG recording and would like to do
> the forward model for the EEG.
>
> So I was trying to use the 'bemcp' and 'openmeeg' as am working on windows
> platform. I have the anatomy of my subject (DICOM file stacked and cleaned
> using SPM).
>
> When I try to use openmeeg, vol.mat is missing from the vol structure
> giving an error message om_minverser.exe doesn't function anymore.
>
> When I try to use 'bemcp', vol.mat contains all NaNs which resulted from
> the c12 and c21 matrices being not a square matrix which makes the inverse
> to be non-existent and also those matrices consists a large number of
> 'Inf' entries.
>
> Like it was mentioned on one of the forums, the error might come when the
> meshes are generated. I was able to find the index of the vertices from
> the Cij matrix, but I couldn't find the actual relation to the
> vol.bnd(i).pnt and vol.bnd(i).tri matrices, 'i' representing either brain,
> skull or scalp.
>
> Here are all the steps that I have followed.
>
> % reading MRI
> mri = ft_read_mri('msGAP724534-0002-00001-000192-01.img');
>
> % segment the brain
> cfg = [];
> cfg.output = {'brain', 'skull', 'scalp'};
> cfg.coordsys = ''; % here I use the RAS coordsys and for the origin 'i'-
> interauricular
> segmentedmri = ft_volumesegment(cfg, mri);
> segmentedmri.anatomy = mri.anatomy;
>
> % prepare mesh
> cfg = [];
> cfg.tissue = {'brain','skull', 'scalp'};
> cfg.numvertices = [3000 2000 1000];
> cfg.transform = segmentedmri.transform;
> bnd = ft_prepare_mesh(cfg, segmentedmri);
>
> % create head model
> cfg = [];
> cfg.method = 'openmeeg';
> cfg.conductivity = [0.33 0.0041 0.33];
> vol = ft_prepare_headmodel(cfg, bnd);
>
> figure;
> ft_plot_mesh(vol.bnd(1),'facecolor','none'); %brain
> figure;
> ft_plot_mesh(vol.bnd(2),'facecolor','none'); %skull
> figure;
> ft_plot_mesh(vol.bnd(3),'facecolor','none'); %scalp
>
> Any help?
>
> Thanks.
> Kidist
>
>
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