Couldn't this "vulnerability" be fixed if they took two scans? Take one of front/back (current approach) and then ask the person to turn 90 degrees and take another scan? to see the sides?
The problem with that is, that it a) doubles the amount of time needed to scan one person and b) doubles the duration of exposure to radiation.
therefore, we'd be better of with metal detectors. Aside from that, the TSA would have to explain, that body scanners are useless without scanning twice and we therefore need to expose you to the double amount of radiation...