For their eyes only?

Scans airport security staff sees would shock passengers, critics say

In a few months, some travelers at Logan International Airport will be asked to let security officials see them naked. While fully clothed, they will be directed to step into a "millimeter wave" machine that resembles a glass elevator. Then, a pair of rotating antennas will emit radio frequency waves to create holograms of their physiques, without clothes.

At another security checkpoint, passengers will be directed to stand against a refrigerator-size backscatter machine as a pencil-thin X-ray beam rapidly scans them to produce textured charcoal outlines of their bodies.

The Transportation Security Administration promises no one will see the revealing images except trained security agents staring at computer screens in a nearby room. And, they say, the body scans will be deleted after agents examine them just long enough to determine whether any suspect materials - such as types of metal, rubber, plastic, or liquid - are concealed beneath the travelers' clothing. That should take about 12 seconds.

Passengers who refuse will most likely have to submit to a physical pat-down.

But the promise of a faster way to detect contraband without actually touching passengers is the primary reason the TSA plans to install 120 of the "whole body imaging" machines in more than 20 of the country's busiest airports by the end of next year. Still, they are stirring up concerns about privacy and health risks.

To address privacy issues raised during the machines' first year of testing at Phoenix Sky Harbor Airport, the TSA has moved agents operating the devices to a separate room so they are unable to match on-screen images with passengers in the flesh. As an additional safeguard, the images aren't saved or transmitted, according to the agency. Also, the three companies that make the whole-body scanners have added software that blurs passengers' faces.

Officials from all three companies say they have adequately dealt with the perceived privacy intrusion. The American Civil Liberties Union, however, is not impressed.

"I liken this to the equivalent of walking naked through a room with a bag over your head while somebody peers from the balcony above you," said Barry Steinhardt, director of the ACLU's technology and liberty program. "Most passengers would be horrified."

Boston airport officials said they are not worried, and they eagerly await the advanced technology. Logan will receive two machines - one millimeter wave and one backscatter - which may arrive before October, said Thomas J. Kinton Jr., chief executive of the Massachusetts Port Authority, which runs Logan. "We're not getting enough for every terminal," Kinton said. "We want more. We're going to push for more."

Logan often is among the first to deploy new technologies, a reminder that the two planes terrorists hijacked on Sept. 11, 2001, to bring down New York's World Trade Center towers departed from Boston's bustling airport. The whole-body imaging machines are already being tested at 10 airports.

The TSA has contracts to buy up to 80 machines - for about $100,000 apiece per backscatter machine and about $170,000 each per millimeter wave machine - from three companies using one of the two technologies: American Science and Engineering Inc. in Billerica, L-3 Communications' Security & Detection Systems subsidiary in Woburn, and Rapiscan Systems, based in Torrance, Calif.

The millimeter wave and backscatter systems work roughly the same way: Within a few seconds, they record how high-frequency radio waves or low-power X-rays bounce off of a body. Skin deflects the energy in ways that other materials, like metal or plastic, do not. So patches of waves or rays that scatter differently will reveal in the images where contraband, such as knives or explosives, are hidden beneath a passenger's clothing.

"We're really looking for edges and contrasts and things that look like they don't belong," said Thomas Ripp, president of Security & Detection Systems, which makes millimeter wave scanners, but not backscatter machines.

With backscatter images, produced by American Science and Engineering and Rapiscan, "we're looking at the intensity of scattered X-rays," said Joe Reiss, American Science's vice president of marketing. "These systems can be very good at finding liquids."

The images produced by millimeter waves cast grayscale holograms - which show buttock bulges, six-pack stomachs, and other parts of a body - against black backgrounds. Those aren't as crisp as the white-background backscatter images that draw a black outline of the body and any concealed objects, so the millimeter wave scans can be harder to interpret and may keep passengers at the checkpoint longer, analysts and backscatter makers said.

L3, which makes the millimeter wave machines, declined to comment.

So far, the TSA hasn't noticed a significant difference in how quickly each technology processes passengers, said spokeswoman Ann Davis. Scanning and image interpretation take 12 to 15 seconds per passenger, she said.

Joshua L. Jabs, a security-technology research analyst at Roth Capital Partners LLC, said it's difficult to determine whether a particular company's whole-body imaging machine is superior to its competition.

"There's probably a six-month delay between the last images that have been publicly published and likely what the companies have in place now," Jabs said. "In the end, I don't think there will be a big difference."

Regarding health issues, however millimeter wave seems to enjoy an advantage over backscatter scanning. Millimeter machines project radio-frequency energy 10,000 times less than what a cellphone or remote garage-door opener transmits, according to the manufacturer. Backscatter machines also emit low levels of energy, relative to how much people are already exposed to in daily life, but the scans carry the stigma of using X-rays.

The radiation dose from a backscatter scan is equivalent to the background radiation passengers are exposed to while flying for two minutes at high altitude, said Reiss. "If they're really worried about radiation, they shouldn't get on a plane in the first place."

David J. Brenner, director of the Center for Radiological Research at Columbia University Medical Center, agrees the radiation dose from a backscatter scan is "extremely low." Still, he doesn't think the TSA should use backscatter machines to X-ray every traveler - especially children, pregnant women, and people who are unaware they carry defective genes that make them more susceptible to radiation.

Brenner coauthored a radiation protection report four years ago to help government agencies decide whether to broaden their use of X-rays. "If you're going to go from New York to Los Angeles, you don't really have a choice about flying," he said. "But perhaps you should have a choice about going through these X-ray machines or not."

Currently, travelers do have a choice. Nine out of 10 passengers at Phoenix Sky Harbor International Airport, where whole-body imaging debuted more than a year ago, have picked energy-beam body scans over pat-downs or being searched with a metal-detector wand, said officials from the TSA, Logan, and the scanner companies. When presenting the option, the TSA referred travelers to a nearby poster that explained how the technology works and how passengers would need to pose, but did not show what the body scan images look like.

As a result, ACLU's Steinhardt said, those passengers were given "a false choice."

"They ought to run that experiment where they show the passengers what the pictures look like," Steinhardt said. "If they put it that way - 'Do you want to go through the naked machine or do you want a pat down?' - it would be different."

Nicole C. Wong can be reached at nwong@globe.com.