No subject

[Sameer Walawalkar]

Hi,

I am currently experimenting with beamformers and was playing with
http://www2.ru.nl/fcdonders/fieldtrip/doku.php?id=fieldtrip:documentation:use_your_own_forward_leadfield_model_in_an_inverse_beamformer_computation
to generate the grid.

I did the following


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];              % center of sphere

% compute the leadfields that can be used for the beamforming
cfg            = [];
cfg.vol        = vol;
cfg.resolution = 2;  % same unit as above, i.e. in cm
grid = prepare_leadfield(cfg, dataPre);

(I expect prepare_leadfield to pick up grad definitions from the data)

??? Error using ==> fieldtrip/private/compute_leadfield
different number of spheres for the radius and origin

Error in ==> prepare_leadfield at 209
   grid.leadfield{dipindx} = compute_leadfield(grid.pos(dipindx,:), sens,
vol, 'reducerank', cfg.reducerank, 'normalize', cfg.normalize);

Error in ==> SomeMaster at 15
grid = prepare_leadfield(cfg, dataPre);



To get around this error, I change vol to

vol.o = [0 0 0 ; 0 0 0 ; 0 0 0  ];

??? Error using ==> fieldtrip/private/compute_leadfield
number of spheres is not equal to the number of coils

Error in ==> prepare_leadfield at 209
   grid.leadfield{dipindx} = compute_leadfield(grid.pos(dipindx,:), sens,
vol, 'reducerank', cfg.reducerank, 'normalize', cfg.normalize);

Error in ==> SomeMaster at 15
grid = prepare_leadfield(cfg, dataPre);


I thought this might be due to the 4 HPI coils, so I changed vol to
vol.r = 12 * [0.88 0.92 0.96 1.00];
vol.o = [0 0 0 ; 0 0 0 ; 0 0 0 ; 0 0 0  ];

but it was of no use.

Any suggestions?

Thanks,
sameer