Privacy concerns are helping thwart large-scale use of high-tech scanners that might have spotted the would-be plane bomber Christmas Day.
Full-body scanners show great detail, including body contours, but critics say they amount to a virtual strip-search. In June, the House voted overwhelmingly to prohibit the use of whole-body imaging for primary screening. They're currently used for primary screening at six airports, and for secondary screening at 13 more.
Supporters say such scanners provide the best protection for the widest range of threats.
Another type of machine is said to give a very accurate and very precise image of things on the body that are not the body. The Transportation Security Administration says it's bought 150 of the so-called "backscatter" machines, which are expected to be deployed next year.