[FieldTrip] overlaying beamformer results to native/normalized space

Akiko Ikkai akiko at nyu.edu
Wed May 4 15:17:49 CEST 2011

I sent a below message to the list last night, but it was bounced back. I'm trying from another email account. My apologies if this was duplicate... 

I'm trying to run beamformer analysis on my MEG data, using DICS, and having difficulty visualizing meaningful results. 

I was able to align MRI image to MEG sensors; after segmentation, ft_prepare_singleshell and  ft_prepare_leadfield, plotting ft_data.grad and volume model confirms that they align reasonably. However, using data.grad, grid, and vol to run ft_sourceanalysis, and ft_sourceinterpolate with MRI (in ctf coordinate system and aligned to MEG sensors) somehow distorts the alignment, and the new volume model does not resemble the original. 

I'm assuming that, after ft_sourceinterpolate, if I segment source_interpolated.anatomy and run ft_prepare_singleshell and ft_prepare_leadfield, it should align with MEG sensors, just as the initial volume model aligned with MEG sensors... or am I making too much of an assumption here? 

Because of the misalignment, output data of ft_sourceinterpolate with "anatomy" and "avg.pow" does not agree with topoplot (run ft_freqanalysis on the same dataset).

If anyone could explain why this alignment distortion might be happening during ft_sourceanalysis and/or ft_sourceinterpolate, I'd really appreciate it.

Thanks in advance, Akiko   

Akiko Ikkai, Ph.D. 
Postdoctoral Fellow
Department of Psychological and Brain Sciences
Johns Hopkins University
Ames Hall, 3400 N. Charles St.
Baltimore, MD 21218

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