[FieldTrip] ft_sourceanalysis & ft_sourceinterpolate

[Akiko Ikkai]

Hi,

I'm working on beamformer with MEG data, and having trouble
making ft_sourceanalysis and/or ft_sourceinterpolate work. It appears that
anatomical MRI and source data do not align, although anatomical MRI
("mri_aligned") and the result of ft_prepare_singleshell ("vol_cm") are both
aligned with MEG helmet.

Is there any way I could verify that the output of ft_sourceanalysis is not
distorted (i.e. same space as input)? I'm using fieldtrip-20110525 version.

Thanks in advance! Akiko

Below is my code:
1. compute the common filter

cfg = [];

cfg.grad            = data_common.grad; % data_common = baseline + left +
right

cfg.grid.xgrid      = -15:0.5:15;

cfg.grid.ygrid      = -15:0.5:15;

cfg.grid.zgrid      = -15:0.5:15;

cfg.inwardshift     = -2;

cfg.vol             = vol_cm; % this is from segmented "mri_aligned"

cfg.channel         = {'all'};

cfg.reducerank      = 2;

cfg.frequency       = 10;

cfg.method          = 'dics';

cfg.projectnoise    = 'yes';

cfg.keepfilter      = 'yes';

cfg.feedback        = 'no';

cfg.realfilter      = 'yes';

cfg.lambda          = '0.005%';

source_common       = ft_sourceanalysis(cfg, freq_common)


2. compute the spatial filter for one of the conditions (using grid & filter
from the step 1)

cfg = [];

cfg.grad            = data_common.grad;

cfg.grid.pos        = source_common.pos; % using grid & filter from the
common filter

cfg.grid.filter     = source_common.avg.filter;

cfg.vol             = vol_cm;

cfg.channel         = {'all'};

cfg.reducerank      = 2;

cfg.frequency       = 10;

cfg.method          = 'dics';

cfg.projectnoise    = 'yes';

cfg.keepfilter      = 'no';

cfg.feedback        = 'no';

cfg.realfilter      = 'yes';

cfg.lambda          = '0.005%';

source_left         = ft_sourceanalysis(cfg, freq_stiml);

source_left.unit    = 'cm';

source_left.dim     = source_common.dim;


3. calculate difference

   source_left_bl          = source_left;

source_left_bl.avg.pow  = source_left_bl.avg.pow ./ source_common.avg.pow;


4. interpolate source to anatomical MRI space

   cfg                 = [];

cfg.method          = 'linear';

source_left_bl_int = ft_sourceinterpolate(cfg, source_left_bl,mri_aligned);
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