We cannot provide universal guidance on areas of study for each exam. Each person finds certain topics easier than others depending on their experience. We can only recommend that you look at the areas we offer and decide which are the easiest for you.
We do know that you will need to review the non-interpretive section (required of everyone) and radioisotope safety.
Our blog has some FAQ's for the MOC exam you may find beneficial. You can read that at: http://www.boardvitals.com/blog/faqs-about-the-radiology-recertification-exam/
Still have questions? Reach out to us here!