How would you know? Whether or not something is protected by copyright is not something you can asses with a blanket statement. Medical images can definitely be protected by copyright.
Can there exist medical images protected by copyright? Definitely I'm you can even find an image made by a photocopier that can be protected by copyright, but that doesn't mean photocopies are usually so.
You're gonna have a hard time convincing a court that your dental radio was in fact creative art.