Is your goal to work as a programmer or go to school? Neither is right or wrong. It might be both depending on the short versus medium term. It might be neither (i.e. the goal might be getting out of medical practice instead -- again nothing wrong with that). Good luck.
Obviously I want to work as a programmer, but I'm wondering if my goals, which require specialised knowledge in topics like security, encryption, cryptopgraphy, medical imaging, databases, would be better learned in university than from a job.
1. Working as a software engineer in healthcare and improving the state of patient data are two different goals. One is technical and vocational and the other is largely a matter of policy and economics and outside the scope of working as a software engineer in healthcare.
2. Engineering is usually a matter of combining existing systems. Detailed academic knowledge of databases is very interesting and mostly irrelevant to engineering an information system that contains databases because there are lots of good databases and because what makes one or the other better is nature of the problem to which they are applied.
3. The same is true for encryption and security. It's a matter of picking tools and/or hiring experts. It's not robustly implementing one's own elliptic curves.
4. There's nothing wrong with pursuing a CS degree for the sake of learning. Just realize that successful engineering is a matter of collaboration and "knowing which table to look at."