[ghthor]

Using bitcoin(I know less about how to store data into bitcoin transactions) you can execute a transaction and store a small piece of data that would be a reference to a larger blob of data, say an IPFS hash to an encrypted MRI image and the doctors notes. You use bitcoin to store the log of changes using reference to some type of immutable data store. It's imperfect, but can be built. The value add of the bitcoin here is it's extremely hard to create a false history and tell that as the real story.

Ethereum would be easier to understand and see what's going on because we have a reasonably readable contract language. You'd still likely need to store larger blobs of data using an external immutable data store, and those blobs wouldn't be automatically distributed and backed up. But you could pay for distributed backups in an automated way using ether. Lots of people working on this last part, which drastically reduces the potential size of the blockchain because it will only be afordable to log blob references and numerical values.