Perhaps, as technology improves, it
  will one day be cost effective to
  take a whole body scan into account.

That's the really funny thing about this: A colossal library of full-body imaging studies over time is exactly the kind of technology that would make that library useable. Think about Google 411 and similar projects: Voice recognition was unusable until people dumped a ton of money into bootstrapping the necessary datasets and now I talk to my phone every day. Similarly, I bet that a bunch of that "anomalies are indistinguishable on images" is solely because we don't have enough images about non-malignant anomalies over time. The data itself would be the technology that makes it usable.