I am new to using fmriprep and trying to determine best practices for distortion correction. My scanning protocol includes both the blip-up/blip-down scans and a GRE sequence. I saw in the fmriprep documentation that the blip-up/blip-down scans take priority for distortion correction (if both types of scans are available and ‘intended for’ the task runs), but I was wondering if anyone knew how this decision was made (i.e., any studies?) or if they have any personal experience with which type of distortion correction tends to work better.
I was having difficulty finding the relevant fmriprep documentation but here it is quoted below from the 0.8.0 version. I specified in all the fmap scans I had (from both the blip-up/blip-down and GRE sequences) that they were IntentedFor the task runs, and this documentation still appears to be accurate (i.e., fmriprep automatically selected blip-up/blip-down instead of GRE/phase difference B0 estimation)
Fieldmap estimation and unwarping workflows
Automatic selection of the appropriate SDC method
If the dataset metadata indicate tha more than one field map acquisition is IntendedFor (see BIDS Specification section 8.9) the following priority will be used:
Schallmo, M.; Weldon, K. B.; Burton, P. C.; Sponheim, S. R.; Olman, C. A. Assessing Methods for Geometric Distortion Compensation in 7 T Gradient Echo Functional MRI Data. Hum Brain Mapp2021, 42 (13), 4205–4223. https://doi.org/10.1002/hbm.25540.
Clarke, W. T.; Mougin, O.; Driver, I. D.; Rua, C.; Morgan, A. T.; Asghar, M.; Clare, S.; Francis, S.; Wise, R. G.; Rodgers, C. T.; Carpenter, A.; Muir, K.; Bowtell, R. Multi-Site Harmonization of 7 Tesla MRI Neuroimaging Protocols. NeuroImage2019, 116335. Redirecting.
Please note that all routines for susceptibility-derived distortion correction have been excised off of fMRIPrep for utilization on other projects (e.g., dMRIPrep). For more detailed documentation onSDC routines, check on the SDCFlows component.
This means that for FMRIPREP v21.0.0 and later, you have to look at how SDCFlows is dealing with priority for distorsion correction. It is not documented but I found the answer in this thread: