Beamforming - filter dimensions
Christine Gruetzner
christine.gruetzner at GOOGLEMAIL.COM
Wed Jul 1 17:19:29 CEST 2009
Dear All,
I'm using LCMV beamforming and I have a question regarding the
dimensions of the filter. We have two different configurations for
LCMV (see below) that result in one-dimensional filters (in the first
case) and three-dimensional filters (in the second case). It seems
that the only difference between the two configurations is the option
cfg.projectmom = 'yes' (in the first configuration) vs. cfg.projectmom
= 'no' (in the second configuration).
Do you have any idea what makes the difference and why I only get
one-dimensional filters in the first configuration? Which would be the
correct options to use?
Best
Christine
%------------------------------------------------------------------
configuration 1:
cfg = [];
% replaced by:
fullnameGrid = strcat(mripath, DesignLCMVSources{i,2});
cfg = load(fullnameGrid);
cfg.vol = cfg.hdm;
%General source computation parameters
cfg.method = 'lcmv';
cfg.lambda = 0.05; % regularization of 0.5%
cfg.powmethod = 'trace'; % compute rms power per dipolelocation
over all available directions
cfg.feedback = 'text'; % give feedback on the progress of the calculations
cfg.keepfilter = 'yes'; % keep the beamformer filters (virtual
electrodes) for later use
%
% cfg.singletrial = 'yes';
cfg.keepmom = 'yes';
cfg.projectmom = 'yes';
cfg.keeptrial = 'yes';
InFilename = strcat(datapath, DesignLCMVSources{i,1});
load(InFilename); % a variable named TLDataOut must exist in the InFile
DataLCMVIn = TLDataOutNew; clear TLDataOutNew; % for clarity of
code remove if too slow
cfg.cov = DataLCMVIn.cov;
DataLCMVOut = sourceanalysis(cfg, DataLCMVIn);
%----------------------------------------------------------------------------------------
configuration 2:
cfgLCMV=[];
% cfgLCMV.frequency = ... % the bandwidth in LCMV comptations is
% chosen in preprocessing (aka FreqLimits)
cfgLCMV.grid=ForwardModel.grid;
cfgLCMV.vol=ForwardModel.hdm;
cfgLCMV.method='lcmv';
% cfgLCMV.projectnoise='yes'; % ???
cfgLCMV.keepfilter='yes';
cfgLCMV.lambda = DICSlambda ; % use the same as for DICS here
cfgLCMV.powmethod = 'trace';
cfgLCMV.fixedori = 'no';
cfgLCMV.projectnoise = 'no'; % these filters are for
computing virtual electrodes later
cfgLCMV.projectmom = 'no';
% computation
cfgLCMV.dim=[Nx Ny Nz]
disp('running LCMV source analysis for common filters/virtual
electrodes')
CommonLCMVSources=sourceanalysis(cfgLCMV,CombiTimelockCov)
----------------------------------
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