[FieldTrip] Pre-whitening/Denoising Elekta/Neuromag Resting State Data

[Sarah]

Hello Fieldtrippers!


I’ve recently learned from this wonderful paper by our very own Fieldtrip
developers “A unified view on beamformers for M/EEG source reconstruction” (
https://www.sciencedirect.com/science/article/pii/S1053811921010612) that -
when working with the Elekta/Neuromag system, if SSS is applied through the
MEGIN software for cleaning (ex. MaxFilter), regularization alone is not
sufficient for good beam former performance. Instead, one recommendation
was pre-whitening in combination with using a truncated pseudo-inverse.


Since I also have MEG data acquired from an Elekta with SSS applied, I am
interested in applying this pre-whitening step on Fieldtrip, particularly
to my resting state data. For pre-whitening of this data, one
recommendation from the paper is using an empty room recording as the
inputted noise data to the pre-whiten function. However, in my case,
unfortunately I do not have these to accompany each of my resting state
recordings.


I was wondering if anyone may have any recommendations on how I may still
follow through with pre-whitening to ensure good beam former performance in
my case. Are there any potential alternatives to the input noise data to
the prewhiten function in Fieldtrip suitable for resting state data (ex.
Something that potentially makes use of the resting state recordings)?


If, on the contrary, it seems that the pre-whiten function is not something
I could use in my case, I would also appreciate any alternate
functions/methods/steps that I could take to still ensure the unwanted
effects of the SSS by the MEGIN software are minimized (ie rank deficiency).



Thanks and I would greatly appreciate any thoughts or suggestions,

Sarah
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