Just in time for the holiday travel crush, concern is on the rise about radiation exposure from the X-ray full-body scanners that are being deployed around the U.S. in an effort to thwart terrorist attacks.
The controversial technology works by bouncing an X-ray beam off a person to create a full-body image that reveals contours, including natural curves as well as any bumps and protrusions from potential weapons that might escape a metal detector such as plastics and ceramics.
The image is displayed on a computer screen in a private room. The person's face is never shown -- and their identity, in theory, is unknown to the airport screener. Passengers can skip the scan and opt instead for a pat-down, which is criticized for being overly personal in the groin area.
Privacy concerns about the scans and pat-down reached fever pitch in recent days when San Diego software engineer John Tyner refused both -- and captured the action with his cell phone's video camera. His blog posts and YouTube videos about the encounter went viral.
While Tyner received a full refund for his ticket and gained Web celebrity status, other interested parties -- ranging from pilots and passengers to esteemed scientists -- are worried that radiation exposure from the X-rays could increase risk of cancers.
The Transportation Security Administration says the amount of radiation from scans amounts to about a thousandth of the amount a person receives from a standard chest X-ray.
Peter Rez, a physics professor at Arizona State University in Tempe, did his own calculations and found the exposure to be about one-fiftieth to one-hundredth the amount of a standard chest X-ray. He calculated the risk of getting cancer from a single scan at about 1 in 30 million, "which puts it somewhat less than being killed by being struck by lightning in any one year," he told me.
While the risk of getting a fatal cancer from the screening is minuscule, it's about equal to the probability that an airplane will get blown up by a terrorist, he added. "So my view is there is not a case to be made for deploying them to prevent such a low probability event."
A group of scientists at the University of California at San Francisco laid out their concerns in a letter to the U.S. Food and Drug Administration, highlighting in particular the potential for the X-ray dose concentrated on the skin to pose a health concern for children and other vulnerable populations, such as people with HIV.
"We are unanimous in believing that the potential health consequences need to be rigorously studied before these scanners are adopted. Modifications that reduce radiation exposure need to be explored as soon as possible," the letter said. Among the signers were David Agard, John Sedat (a professor emeritus) and Robert Stroud, all professors of biochemistry and biophysics; and Marc Shuman, professor of medicine.
In response, the Food and Drug Administration said the technology has been reviewed Sandia National Laboratories, the FDA, National Institute for Standards and Technology and Johns Hopkins University.
"In summary, the potential health risks from a full-body screening with a general-use X-ray security system are minuscule. Several groups of recognized experts have been assembled and have analyzed the radiation safety issues associated with this technology. ... As a result of these evidence-based, responsible actions, we are confident that full-body X-ray security products and practices do not pose a significant risk to the public health," the FDA said.
Arizona State University's Rez voiced other concerns: What's the potential for one of the scanners to fail, given that they will run all day, every day at airports across the country? When that happens, are safety mechanisms in place to prevent overexposure to radiation? Rez also said that the scanners are "useless for detecting explosives."
Janet Napolitano, secretary of the Department of Homeland Security, weighed in on the controversy with an op-ed on Monday in USA Today. She reiterated the government's view that independent evaluations show the technology to be safe and hammered home why the federal government deems the scans and pat-downs necessary:
"Each and every one of the security measures we implement serves an important goal: providing safe and efficient air travel for the millions of people who rely on our aviation system every day."
The question remains, though, are these X-ray scanners more harmful than helpful? Feel free to weigh in with your comments below.
John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on http://twitter.com/b0yle.