[FieldTrip] problem with MEG leadfield

[Lilla.Magyari at mpi.nl]

hi Sara,

I am not entirely sure of this: But I think you get the error message
because your vol structure is recognized as a concentric-spheres type
volume conduction model which is supported for EEG data, while your input
is MEG data.
You can check it here (in the reference documentation of
ft_prepare_headmodel) which headmodels are implemented for MEG:
http://fieldtrip.fcdonders.nl/reference/ft_prepare_headmodel.

Best,
Lilla


> Hi everybody
> I'm trying to generate a field for a simulated dipole using the
> command ft_dipolesimulation, for a MEG study.
>
> I do the following:
> -read the hdr
>
> -import the sensor structure with the following lines
> grad=hdr.grad;
> radius = sqrt(sum(grad.chanpos.^2,2));
> grad.chanpos = grad.chanpos./ [radius radius radius];
> grad.label=hdr.label(1:306)';
>
> -then I create the vol structure using the following code
> vol = [];
> vol.r = 12 * [0.88 0.92 1.00]; %   radii of spheres, the head radius is 12
> cm
> vol.c = [1 1/80 1];       % conductivity
> vol.o = [0 0 0];
>
> At this point I have the grad structure, and the vol structure.
> Then I give all the options for the dipole simulation with the code
>
> %% create a dipole simulation with a custom timecourse
> cfg      = [];
> cfg.vol  = vol;      % see above
> cfg.grad = grad;     % see above
> cfg.dip.pos = [0 0.5 0.3];
> cfg.dip.mom = [1 0 0]';
> cfg.dip.frequency = 10;     %Hz
> cfg.ntrials = 10;
> cfg.triallength = 20;        % seconds
> cfg.fsample = 250;          % Hz
>
> but when I try to esecute the line
>
> raw1 = ft_dipolesimulation(cfg);
>
> I find this error
>
> ??? Error using ==> ft_compute_leadfield at 301
> unsupported volume conductor model for MEG
>
> Error in ==> ft_dipolesimulation at 198
>    lf = ft_compute_leadfield(dippos{trial}, sens, vol);
>
>
> I really cannot understand why  volume conductor model is not supported.
> Any suggestion? I'm pretty sure that the mistake is trivial, but I'm
> not able to see it.
>
> Thank you!
> Dott.ssa Sara Rombetto
>
>   Istituto di Cibernetica
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>
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