The airport became one of the first 11 in the country to receive the so-called advanced imaging technology (AIT) units, purchased with money from the American Recovery and Reinvestment Act (ARRA).

"Imaging technology safely screens passengers for metallic and nonmetallic threats -- including weapons, explosives and other objects concealed under layers of clothing -- without physical contact, to help the TSA keep the traveling public safe," said Lee R. Kair, assistant administrator for security operations with the U.S. Transportation Security Administration, during a news conference at Logan Airport.

The units, which have drawn fire from privacy advocates for their somewhat-revealing body scans, use backscatter technology to project low-level X-ray beams over the body. Once passengers enter a unit, they stand with their feet shoulder-width apart and their arms raised. X-rays are bounced off the body, and the returning rays produce an image that is viewed by a TSA agent about 50 feet away in a sealed room. The resembles a chalk etching. If screeners detect a threat or anomaly, they can radio for another agent to make a closer inspection.

Trying to quell privacy concerns, Kair said: "The officer attending to the passenger will not view the image. As an additional precaution, the officer viewing the image will be remotely located and the image won't be stored, transmitted or printed and will be deleted immediately once viewed." He added that the machines have "zero storage capability."

The scan and review of the image takes about 20 seconds, and Kair said the units should not slow the passenger screening process. In fact, more time is spent checking and X-raying carry-on baggage, he said.