SEBASED intensity bias field correction

[McKenzie Hagen]

Hello! 

I have a question about the processing for the 2025 data release. 

In the Glasser et al., 2016 Nature paper that was cited in reference to the SEBASED field correction, the reference image computed from the Sbref and spin echo phase reversed images was used only on the task beta maps, and not during any processing. For the updated data release, was the SEBASED correction applied in the same step as the legacy bias field correction? This is what it seems like from GenericfMRIVolumeProcessingPipeline.sh, but I just want to double check that I'm not missing something. 

Related, in the appendix of Glasser et al., 2016 Nature Neuroscience, it's stated that "For some fMRI analyses (e.g., resting-state correlations and task z-statistics), bias correction of fMRI is not needed. However, for other analyses (e.g., beta maps, variance maps), an fMRI intensity bias field can make the data less biologically interpretable across the whole image" (page 6). Has there been other work done in the last 10 years that makes bias field correction more relevant for rsfMRI, or is there other motivation? Or should the interpretation of "Spin-echo based ("SEBASED") intensity bias field correction of all the fMRI data" in the data release announcement be "all the task fMRI data"? 

Thank you in advance! 

McKenzie

[Glasser, Matthew]

1. For the tICA cleaned fMRI data (resting state and task), we did also fix the bias field.  It was done in the timeseries, rather than after the fact on all the maps, but it is a simple multiplicative map.
2. Yes, we have moved more towards covariance and amplitudes, rather than correlations, and proper bias correction is important for both.

Matt.

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