I could see them using some sort of x ray machine for all passengers or selected passengers, The x ray machines would probably catch something like that. My guess is they could probably take x rays of individuals secretly when they walk through the metal detectors or maybe newer redesigned metal detectors with x ray capabilities that some one would be looking at on the other side of the wall.
Yes, yes, but then itll get out that they were doing this, and therell be a million lawsuits, what with people claiming they got cancer from em, and whatnot