FMRIPREP: field mapping data

Dear Siemens users,

So- what is the standard way to split these combined 4d series to magnitude and phasediff?
Going through the whole sequence, getting the indices (of changes from phase to magnitude) and splitting by them is the only way, or there is some shortcut for this?

@Chris_Rorden
Sorry for the newbie question, but-
When converting Siemens gre_field_mapping sequences to the nifti format by running dcm2niix, one finds:
_e1
_e1_eq_1

_e2
_e2_eq_1
_e2_ph

How does one should transform these to the magnitude and phase nii-s- which is which?
(Any documentation regarding these suffixes?)

Many thanks