beamformer on yokogawa data, megplanar.m

Sangita Dandekar sangita.dandekar at GMAIL.COM
Tue Feb 2 18:22:30 CET 2010


Am hoping to apply beamforming based source localization to MEG data from a
Yokogawa system.   Think I've managed to coregister MRI and sensor
coordinate systems, so that part of the problem is pretty much under

What I'm wondering about is what the assumptions are of the
prepare_leadfield and other source localization scripts about the input
gradiometer data.  Haven't looked at it too closely yet, but does it assume
that the input sensor data is planar gradient data?  If so am assuming that
inputting the raw data from the Yokogawa system (axial gradiometers) is
incorrect?   Or does fieldtrip distinguish between different types of
gradiometers using the input .grad structure?

I tried to convert the axial gradiometer data from the yokogawa system to
planar gradient data by using the megplanar function as shown below, and
receive the following error:
(Even if it isn't necessary for source localization, it would be nice to be
able to view the data as planar gradient data)

>> cfg=[];
>> cfg.planarmethod='sincos';
>> megplanar(cfg, righttrials);
the input is raw data with 156 channels and 46 trials
??? Error using ==> checkdata at 478
This function requires ctf151, ctf275, bti148 or bti248 data as input, but
you are giving meg data.

Error in ==> megplanar at 228
data  = checkdata(data, 'datatype', {'raw' 'freq'}, 'feedback', 'yes',
'ismeg', 'yes', 'senstype', {'ctf151', 'ctf275',
'bti148', 'bti248'});


Some background information:  used the ft yokogawa2grad.m function (stored
in private FT directory) to create the gradient structure.  Here is what
data structure for
one set of trials looks like:

>> righttrials

righttrials =

      trial: {1x46 cell}
      label: {1x156 cell}
       time: {1x46 cell}
    fsample: 500
       grad: [1x1 struct]
     offset: [46x46 double]
        cfg: [1x1 struct]

>> righttrials.grad

ans =

      pnt: [314x3 double]
      ori: [314x3 double]
      tra: [157x314 double]
    label: {157x1 cell}
     unit: 'cm'


Thanks in advance for any help!

The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also and
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