[FieldTrip] generating single / multiple local sphere model using brain surface from segmented MRI

[Robert Oostenveld]

Hi Andreas

Based on the segmentation a set of vertices/points is constructed for the surface. The spheres are subsequently fitted to those vertices/points. 

3000 vertices sounds like a good number.

best
Robert


On 24 Mar 2011, at 6:23, Andreas Wollbrink wrote:

> Hi all,
> 
> I just tried to generate a multiple local sphere model using a brain surface from a segmented MRI following the instructions on
> 
> http://fieldtrip.fcdonders.nl/example/make_leadfields_using_different_headmodels#local_spheres_model_from_fieldtrip_using_brain_surface_from_segmented_mri
> 
> The actual matlab code is:
> 
> hdr = ft_read_header('example.ds');
> cfg                       = [];
> cfg.grad                  = hdr.grad;
> ft_segment                = ft_prepare_localspheres(cfg,segmentedmri);
> 
> 
> The error message is as follows:
> 
> ??? Attempted to access cfg.numvertices(1); index out of bounds because numel(cfg.numvertices)=0.
> 
> Error in ==> prepare_mesh_segmentation at 67
>  [pnt, tri] = triangulate_seg(seg, cfg.numvertices(i), ori);
> 
> Error in ==> ft_prepare_mesh at 104
>  bnd = prepare_mesh_segmentation(cfg, mri);
> 
> Error in ==> ft_prepare_localspheres at 93
>  headshape = ft_prepare_mesh(cfg, mri);
> 
> 
> The same error occurred when I tried to generate a single local sphere model based on a brain surface derived a segmented MRI.
> 
> 
> After defining a value for cfg.numvertices = 3000 I got a reasonable good volume conductor model.
> 
> Since I am not quite sure which value I should use for the numvertices parameter I like to ask for some explanations and suggestions.
> 
> Thanks in advance!
> 
> Andreas
> -- 
> 
> 
> ======================================================================
> 
>  Andreas Wollbrink, Biomedical Engineer
> 
>  Institute for Biomagnetism and Biosignalanalysis       	
>  Muenster University Hospital
> 
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>                        e-Mail: a.wollbrink at uni-muenster.de
> 
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