Kair said the backscatter units are safe and that the radiation exposure is equivalent to what a passenger would experience in an aircraft for two minutes at 30,000 feet.

The TSA began piloting AIT units in February 2007.

While the scanners will be used as a primary screening method at Logan, passengers are not required to be scanned and can request a pat-down and metal detection instead. Kair said there had been a 98 percent acceptance rate for the units among passengers at trial locations.

Another type of AIT unit that is not being deployed in Boston uses "millimeter wave" technology and produces an that resembles a fuzzy photo negative.

Other airports that will soon receive the AIT units are Fort Lauderdale-Hollywood International, Mineta San Jose International, Port Columbus International, San Diego International, Charlotte Douglas International, Chicago O'Hare International, Cincinnati/Northern Kentucky International, Los Angeles International, Oakland International and Kansas City International.