I never really understood radiology physics until this book put it all together for me. Just very test-oriented and high yield throughout without much unnecessary fluff. I would highly recommend this as the primary method for studying for the boards.

Downside is that there are many errors. Some are clearly typos, others are straight contradictions/wrong statements. Just be careful. If a statement doesn't make sense, look it up elsewhere and see if it's actually accurate. You risk acquiring some black pearls because of this, but this still remains the best currently available source for boards radiology physics in my opinion.