Make the data representation structure more generic to accommodate both DWI and PET

[mnoergaard]

What would you like to see added in this software?

Currently, there exist a /data/pet.py and a /data/dmri.py used to create a data representation structure with similar but slightly different methods. It would be ideal, if we could work towards creating an abstract base class for a data representation structure, that can then be adapted to align with e.g. PET or dMRI specific needs.

Do you have any interest in helping implement the feature?

Yes

Additional information / screenshots

No response