SyN-based susceptibility distortion correction not carried out when using --use-syn-sdc

[rbakker]

Summary

The --use-syn-sdc flag is supposed to invoke SyN-based susceptibility distortion correction, however the flag has no effect at all.

Additional details

Preprocessing was performed using QSIPrep 1.0.1.dev0+gee9aa2e.d20250115 [@cieslak2021qsiprep]

What were you trying to do?

Run QsiPrep with SyN-based susceptibility correction

What did you expect to happen?

That SyN-based susceptibility correction was performed.
The work-around is to use the flag --force-syn,
but according to the documentation that flag should be used to use SyN-based susceptibility correction in addition to fieldmap based correction.

What actually happened?

Susceptibility correction was not used at all.
See also the expected behavior as described here:

qsiprep/qsiprep/workflows/fieldmap/base.py

Line 25 in fc89945

Fieldmaps found ``use_syn`` ``force_syn`` Action

Reproducing the bug

To reproduce the bug just run QsiPrep on a dataset that does not have fieldmaps or reverse phase encoding available with the option --use-syn-sdc. To speed up testing --boilerplate-only can be specified, because from the boilerplate text it is already clear whether syn-sdc is included in the workflow.

-->