Its lab tests, ekg's, and radiologic studies. HIDA's, noggin ct's, CXR's, Abd XRays, stuffs like that. There is a page in Crush Step II that has all the gold standard tests to order for radiology. Should be able to pound it in 10 minutes.
You won't be prepared for many of the questions on the exam though. Doesn't matter what you read.
I still stand by:
High Yeild OB GYN
NMS step III