It wasn’t a lead story when scientists from the University of California at San Francisco first publicly expressed their unease earlier this year about the possible negative health effects caused by full-body airport scanners now being used across the United States to stop explosives from making it onto jet airliners.

By then the Transportation Security Administration had largely managed to remove itself from headlines announcing privacy complaints some were making about the devices, which allow security screeners to see underneath the clothing of passengers unlike traditional metal detectors.

Powerful members of Congress have since begun to throw their weight behind the issue, however, threatening to place whole-body imagers back in the spotlight as the federal government continues to spend tens of millions on them, much of it from economic stimulus dollars.

This month Republican Sen. Susan Collins of Maine, ranking member of a key committee that oversees the Department of Homeland Security, sent a letter to Secretary Janet Napolitano raising questions about the federal government’s decision in May to purchase 100 more scanning devices, particularly those using so-called “backscatter X-ray” technology.

Joined by fellow GOP senators Tom Coburn (Okla.) and Richard Burr (N.C.), Collins requested that the department’s chief medical officer and a group of independent experts review the health impacts of full-body scanners on airline travelers, employees of the TSA and other airport personnel. The trio wants homeland security officials to find out what happens as a result of repeated exposure to radiation from the machines.

“Please explain why the department continues to purchase this technology when legitimate concerns about its safety appear to remain unanswered,” they wrote.

The four medical experts at UCSF warn that whole-body imagers could subject the skin to “dangerously high” doses of radiation because of the unique technology used. They’re worried certain travelers may be particularly vulnerable to emissions from the scanners including seniors, women prone to breast cancer, expectant mothers and children for which the impact hasn’t been fully evaluated.

Their own April 6 letter to President Obama’s top science advisor says independent safety data on the devices do not exist to determine if radiation damage is occurring. The UCSF scientists are hardly first-year med students. One is a biophysicist, while another is an internationally known cancer expert. Three are members of the National Academy of Sciences. According to their letter:

Crises create a sense of urgency that frequently leads to hasty decisions where unintended consequences are not recognized. Examples include the failure of the [Centers for Disease Control and Prevention] to recognize the risk of blood transfusions in the early stages of the AIDS epidemic, approval of drugs and devices by the [Food and Drug Administration] without sufficient review, and improper standards set by the [Environmental Protection Agency], to name a few.

The more recent crisis they’re referring to is the failed Christmas Day bombing when would-be radical Umar Farouk Abdulmutallab allegedly tried to blow up a Northwest Airlines flight on its way to Detroit. That set off a campaign to more rapidly implement full-body scanning at airports around the globe, including several in the United States and those in the Netherlands and Nigeria where Abdumutallab reportedly boarded connecting flights with explosives hidden in his underwear.

One maker of whole-body imagers, California-based OSI Systems, has since begun boasting to investors about the surge in demand reporting that total orders stood at $50 million worth as of mid-May. Authorities in Great Britain also announced this year following the attempted attack that they would be purchasing scanners from the company.

Meanwhile, federal officials have been able to quell some grievances over privacy associated with the machines by promising the flying public that images generated from them would not be stored or transmitted. Security officers also review the images in a separate room preventing workers from seeing the actual passenger, TSA says. Those assurances haven’t stopped some briefly high-profile and even bizarre incidents from occurring.

A whole-body imager in May led to one situation seemingly worse than any dreadful scenario a privacy advocate could dream up as evidence against their use. The Smoking Gun obtained a police report showing that an airport screener had beat his co-worker with a baton causing “bruises and abrasions” after he was teased relentlessly by fellow security officers for having a small penis.

How were they familiar with the size of his genitals? It was revealed during a training session involving an X-ray scanner. The man “stated he could not take the jokes anymore and lost his mind,” according to the report.

Sen. Collins had already been asking the Department of Homeland Security why it wasn’t using whole-body scanners like those deployed in Amsterdam that rely on software to automatically detect the presence of dangerous items on flyers as they pass through security gates. That way screeners don’t need to review detailed images or conduct further inspection unless the program alerts them to a possible threat.

She wrote in a separate mid-April letter to the department that Amsterdam’s scanning machines are faster at moving travelers past security and they also prevent passengers and screeners from being exposed to radiation.

While no technology is 100 percent effective at detecting dangerous items, the Dutch officials we talked to expressed confidence that there was a high probability that this technology would have detected Abdulmutallab’s concealed explosives. We wanted to bring this technology to your attention because it appears to offer a solution to the significant privacy concerns that have been raised about DHS’s deployment of whole-body imaging machines in the United States.

The letter was co-signed by senators Jon Kyl (R-Ariz.) and Saxby Chambliss (R-Ga.).

Flickr image courtesy Mad House Photography.

G.W. Schulz is a reporter for Reveal, covering security, privacy, technology and criminal justice. Since joining The Center for Investigative Reporting in 2008, he's reported stories for NPR, KQED, Wired.com, The Dallas Morning News, the Chicago Tribune, the San Francisco Chronicle, Mother Jones and more. Prior to that, he wrote for the San Francisco Bay Guardian and was an early contributor to The Chauncey Bailey Project, which won a Tom Renner Award from Investigative Reporters and Editors in 2008. Schulz also has won awards from the California Newspaper Publishers Association and the Society of Professional Journalists’ Northern California Chapter. He graduated from the University of Kansas and is based in Austin, Texas.