[FieldTrip] Error in DICS Source Localization (Beamformer)

[Tzvetan Popov]

Dear Helen,

you seem to compute the source model on the fly. From the feedback "642 dipoles inside, 0 outside" I suspect some mismatch between the units of the geometrical objects (i.e. headmodel, sourcemodel, electrodes).
Could you please execute the following where vol is the headmodel (3rd compartment of the bem model), grid your sourcemodel and elec your electrodes:

    figure;
    ft_plot_vol(vol, 'edgecolor', 'none'); alpha 0.4;
    ft_plot_mesh(grid.pos(grid.inside,:));
    ft_plot_sens(elec, 'style', '*g');

best
Tzvetan


> Dear Fieldtrip Users,
> 
> In attempting to use Beamformer source localization, I get an error when computing ft_sourceanalysis with the code below:
> 
> cfg = [];
> cfg.method = 'dics';
> cfg.frequency = 6;
> cfg.elecfile = 'GSN_HydroCel_129_short.sfp';
> cfg.vol = vol;
> cfg.dics.projectnoise = 'yes';
> cfg.dics.lambda = '5%';
> cfg.dics.keepfilter = 'yes';
> cfg.dics.realfilter = 'yes';
> sourceAll = ft_sourceanalysis(cfg, freqAll);
> 
> the call to "ft_selectdata" took 0 seconds and required the additional allocation of an estimated 0 MB
> using headmodel specified in the configuration
> reading electrodes from file 'GSN_HydroCel_129_short.sfp'
> converting units from 'cm' to 'mm'
> determining source compartment (1)
> projecting electrodes on skin surface
> combining electrode transfer and system matrix
> creating dipole grid based on inward-shifted brain surface from volume conductor model
> using headmodel specified in the configuration
> using gradiometers specified in the configuration
> 642 dipoles inside, 0 dipoles outside brain
> the call to "ft_prepare_sourcemodel" took 0 seconds and required the additional allocation of an estimated 42 MB
> selection crsspctrm along dimension 3
> 
> Attempted to access noise(0); index must be a positive integer or logical.
> 
> Error in beamformer_dics (line 211)
>     noise = noise(end);
> 
> Error in ft_sourceanalysis (line 662)
>           dip(i) = beamformer_dics(grid, sens, vol, [],  squeeze(Cf(i,:,:)), optarg{:});
>  
> 
> I note that it runs without errors when I change cfg.dics.projectnoise to 'no' - but what implications does that bring? I find with that change I can make it through the rest of the Beamformer tutorial (the section on contrasting conditions) without explicit errors, but I nevertheless receive the following messages, following which my plotted figure is simply blank! Something is going wrong, I think.
> 
> (1)
> sourceDiffInt = ft_sourceinterpolate(cfg, sourceDiff, mri);
> Warning: use cfg.parameter='pow' instead of cfg.parameter='avg.pow' 
> > In ft_checkconfig (line 139)
>   In ft_sourceinterpolate (line 119) 
> 
> (2)
> ft_sourceplot(cfg, sourceDiffInt);
> Warning: use cfg.funparameter='pow' instead of cfg.funparameter='avg.pow' 
> > In ft_checkconfig (line 139)
>   In ft_sourceplot (line 210) 
> Warning: use cfg.maskparameter='pow' instead of cfg.maskparameter='avg.pow' 
> > In ft_checkconfig (line 139)
>   In ft_sourceplot (line 213) 
> the input is segmented volume data with dimensions [128 128 128]
> not plotting anatomy
> Warning: could not determine dimord of "pow" in the following data 
> > In getdimord (line 516)
>   In ft_sourceplot (line 390) 
> 
> Anyone know what might be the problem? Thanks very much!
> 
> Helen Wieffering
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> fieldtrip at donders.ru.nl
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