The nuclear stress images are fairly straightforward, but lots of questions on subsegments of vessels so know the territories cold. For example, I remember one question asking if the territory was: (1) proximal LAD, (2) mid-LAD, (3) high rising diagonal, (4) mid-diagonal, (5) left circumflex.
Overall, I thought they were harder than people made them out to be. There were a lot of questions on physics and isotopes so definitely spend time going over that material. They also ask questions on radionuclide ventriculography including first vs. second pass, etc., so make sure to review that also.
For me, in terms of boards I felt that in terms of difficulty:
CT/MRI << Gen card < Nuclear = Echo
