Moi Chris,
In principle, both ways are fine if the SSS origin is set properly.
If you are doing only source-level analysis, you should not use the trans-option at all and 1a) is the choice.
If sensor-level signals are compared, you can continue to 1b) if 1a) was already done. Then you need to add options ‘-autobad
off –force’, because by default there are no bad channels after 1a), and ‘-force’ is needed because otherwise maxfilter complains that SSS was already applied and stops. In 1b, the program recomposes the inside basis amplitudes, and reconstructs the MEG signals
corresponding to the default head position.
Using 2), you save time and disk space. However, I recommend to use tSSS always together with movecomp, because head movements
often generate nearby artifacts which are not removed by plain SSS.
I am finalizing a report on the effect of the origin choice in trans-operations, and will share it with you soon.
BR, Jukka
Jukka Nenonen |
Method Development Manager |
From: Announcement for the Neuro MEG list [mailto:[log in to unmask]]
On Behalf Of Christopher Bailey
Sent: 29. tammikuuta 2018 16:38
To: [log in to unmask]
Subject: Maxfilter: running "-trans default" on already SSS'd files
Dear Jukka,
Are these two Maxfilter-pipelines equivalent:
1a) Run maxfilter with tSSS and movecomp, compensate movement to initial head position -> output_1a_tsss_mc.fif
1b) Use output_1a_tsss_mc.fif as input to maxfilter, which is run with
-trans default as the only option
2) Run maxfilter with tSSS and movecomp with -trans default as the only option (no temporal extension, plain SSS)
If yes (1 & 2 are equivalent), can you shed any light on how 1b) actually implements the translation? Are the SSS coefficients estimated anew from the now tSSS + MC’d data (output_1a_tsss_mc.fif)? Then I would expect the results to differ,
though…?
Best,
Chris
--
Christopher Bailey, MSc
MEG Engineer, MINDLab Core Experimental Facility
Center of Functionally Integrative Neuroscience (CFIN)
Aarhus University, Denmark
tel. cell: +45-2674-9927
tel. office: +45-7846-9936