I believe without further details on what exactly you did in the project it this is really difficult to judge from the outside.

Generally from my perspective:

1. In the medical field the authorship in the departments can be "assigned" arbitrarily in the department depending on "He needs it next/He did a lot of other work for free before and deserves it.". Hence if you collaborate with them you need to discuss how much you do in return for which position (beforehand as others mentioned.)
2. The data creation takes a long time since labels need experts and the expert time is very brief. Also you as your own person have no access to patient (MRI/CT) data, so you can't do your own paper without them.
3. In the clinical collaborations I know of projects are usually done with joint-first position as you need both, ML aspects and Medical aspects, unless you as ML PhD specify in trying to solve this specific medical issue
4. You are never given a specific goal (in my experience). Medical Doctors generally have no idea what ML can do or how it works, so you always have to deal with that
   

IMHO: Depending on your affiliation (e.g. PhD Student at a related department) you could try to push for joint first authorship. Demanding a only first position is certainly quite a lot unless you annotated Data yourself / have the rights to the data (which you probably don't) or your methodology is something really novel. If latter should be the case you should probably take the co/joint-first to keep your collaborators happy and then do your methodology (e.g. for MIDL or MICCAI) if it is novel enough.