[FieldTrip] fit volume segment and sensors

s.rombetto at cib.na.cnr.it s.rombetto at cib.na.cnr.it
Sun Dec 8 20:46:55 CET 2013

Dear Fieldtrippers

I 'm trying to perform source analysis on MEG data.
I use an AtB system (usually it is described as 'itab' in fieldtrip)

First I have preprocessed my data and I have calculated the cross  
spectral density matrix

Then I have constructed the forward model

  mri = ft_read_mri('Subject01.mri');
cfg = [];
cfg.write      = 'no';
cfg.coordsys   = 'ctf';
[segmentedmri] = ft_volumesegment(cfg, mri);

and segmented the brain surface:

cfg = [];
cfg.method = 'singleshell';
vol = ft_prepare_headmodel(cfg, segmentedmri);

With the command ft_read_sens I have also read the sensors positions.

Before going on I have checked the results plotting the volume and the  
sensors using the commands
vol = ft_convert_units(vol,'cm');
sens = ft_read_sens(rawdataname);
ft_plot_sens(sens, 'style', '*b');
hold on

and I have noticed that the result is wrong because the volume soesn't  
fit the sensors as shown in the attachment
Moreover, following some topics in the mailing list I have used


and I have found that the coordinate systems are diffeerent.

As far as I understand I should use the ctf coordinate system to  
perform the source analysis. But even if I try to specify this  
coordinate system it did not work.
Any suggestion to solve this problem?

Kind regards
  Dott.ssa Sara Rombetto
  Istituto di Cibernetica
  "E. Caianiello"
  Via Campi Flegrei, 34
  80078 Pozzuoli (NA)
  mob +39 3401689815
  tel +39 0818675361
  fax +39 0818675128
"I disapprove of what you say, but I will defend to the death your  
right to say
it." [Evelyn Beatrice Hall, The Friends Of Voltaire]

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