[FieldTrip] append CTF grad structures

[Matthias Franken]

Hi all,

I have a question with respect to the ‘grad’ structure in my CTF MEG data. For a given participant, data acquisition was stopped and restarted, leading two (or more) raw data files, with only a short break in between. The participant did not leave the MEG in between.
I would like to append the two datasets to preprocess them together, as if they were acquired in a single run. I am wondering though how to deal with the grad structure, given that the ft_appenddata seems to remove it. I am guessing this is due to slight differences in the coil and chan pos/ori matrices, presumably a result of slight head movements. Up til now, I was simply using the first file’s grad structure, but I guess there should be a better way. Would the most straightforward way be to average the positions and orientations in the grad structures of each run to get at a grad structure for the appended dataset? I.e., would this be closest to the grad structure that I would have gotten if data acquisition wouldn’t have been interrupted?
Or should I realign each using ft_megrealign? Though I am guessing this is not what just doing acquisition in one run would lead to either.

Thanks!



---
Matthias Franken, PhD
Postdoctoral Researcher
Motor Neuroscience Lab
Department of Psychology
McGill University

matthias.franken at mail.mcgill.ca<mailto:matthias.franken at mail.mcgill.ca>
https://frankenmatthias.github.io/homepage




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