For the USMLE: The only radiology pictures that I had was of MRI/CT scans for neuroanatomy (use high yield neuroanatomy for this), and I think I remember having one X-ray of a bone tumor, but the question was all you needed to answer the question. I never used a "radiology textbook", but for cross sectional anatomy, I did purchase a red book, I think that it is called "Cross sectional anatomy"; I'm not so sure but the authors are from my school so I'm not so sure how universally helpful that book might be (I bought it because I was worried that a prof might pull questions from it). Unless you have a class called radiology, the best way to understand radiology right now is just to know the anatomy (high yield gross anatomy book for this). First Aid has some nice radiology pictures too, but wait until the beginning of second year (use it with your second year classes) to purchase first aid because they come out with a new edition every year. Anyways, studying radiology= low yield for the USMLE. Some of my classmates who said that they had CT scans of neuroanatomy told me that their questions were so random that they would have done a few years of radiology residency before they could get those right.