Someone further down the thread linked a piece about x-rays, but in general I'd suspect that an MRI or other visual produced by medical scanning technology would not be copyrightable in the first place; copyright does require a certain amount of creative effort in the production of the copyrighted work. The important case here, if you want to look up the history, is Feist v. Rural Telephone, which dealt with the (non-)copyrightability of a list of telephone numbers.