The Transportation Security Administration (TSA) operates more than 700 body scanners at about 180 airports across the country.
TSA officials say the millimeter wave machines are being moved into high-traffic airports like Los Angeles International because they can screen each passenger in about 10 seconds. The backscatter scanner can take up to a minute.
The machines were introduced at American airports after a Nigerian national tried to blow up a US airliner near Detroit with explosives hidden in his underwear on December 25, 2009.
About half of those scanners employ "backscatter" technology that uses low-level X-rays to create what resembles a nude image of passengers to detect weapons. The faster scanners use low-level radio waves, or millimetre waves, and instead use a generic avatar figure to show hidden objects, the Los Angeles Times reported.
The backscatter machines have been criticised by academics and privacy advocates who say the radiation they emit poses a health risk and the images they create violate the privacy of passengers.
Torrance-based Rapiscan Systems Inc., the makers of the backscatter machines, declined to comment, the paper said.
Meanwhile, Brandon Macsata, executive director of the Association for Airline Passenger Rights, said he does not believe the TSA's reason for switching out the machines.
"It's hard to believe what they say," he said, citing previous TSA statements about the privacy of the scanners that Macsata said have been false.
