Additional key/value pairs for B1+/B1- images?

[ChristophePhillips]

So far the only 2 key/value pairs available for the B1+ maps in the fmap folder are _acq-<acq-label> and _run-<run_index>. This does not seem sufficient for the characterization of the B1+/- maps for the hMRI toolbox example dataset.

Using these example data,

• B1+ maps are acquired for a series of 11 flip angles and 2 acquisition types (SE/STE). It would therefore be useful to use indexable metadata _fa-<index>.
• B1- maps are acquired separately for the 3 anatomical images types (MTw, PDw and T1w) and the 2 coils (head and body), i.e. 3x2 images, each corresponding to a different acquisition type. Both information must appear in the filename otherwise 2 or 3 files would end up with the filename. Could the _mod-<mod-label> key/value pair be used for the 3 image types (MTw, PDw and T1w)?

Potential issues though:
Currently the _mod-<mod-label> key/value pair is only used for the case of a _defacemask.nii mask image, in order to associate this mask with the corresponding modality image, see here.
Plus, with MPM data, the suffix of the anatomical images is actually _MPM, and the image type defined in the _acq-<acq-label> key/value pair! So the _mod-<mod-label> may not be ideal...