Physicians are taught to do exams that are cost-effective (costs including time, money, costs of false positive, costs of patient fears/anxiety etc).

I don't think anyone at the TSA understands these concepts. To me it is quite clear that they make the pat-down as unappealing as possible to have people go through the body scanners. (As a radiologist, radiating millions of people a day even at very low doses is appalling, and I'm still waiting on someone to explain to me how these scanners could use a type of energy that penetrates clothing but not skin.) I don't know if there is some kind of lobby from the companies making the machines or what, I'm not sure how someone decided that metal detectors were not effective enough.

Then again, considering what comes from government bodies on health care, I guess I can't be surprised at what they decide is worth their money and time.