Government officials have announced plans for wider use of full body scans at U.S. airports. What are these devices, and are there any associated health risks?

Full body scanners: what are they?

The Transportation Security Administration (TSA) was created following 9/11 to safeguard the nation's transportation systems. Since 2007, the TSA has been piloting the use of advanced imaging technologies to screen for security threats. The newest devices use millimeter wave imaging and backscatter scanning.

Millimeter wave imaging technology uses high-speed radio waves beamed over the body's surface to construct a three-dimensional image. Backscatter scanning uses low level x-rays to create a two-sided image.

"They all fall into the same spectrum of electromagnetic energy," said Dr. James Duncan, interventional radiologist for Barnes-Jewish West County Hospital. "Micro-wave would be at one end of the spectrum, x-ray at the other." The amount of electromagnetic energy emitted by the millimeter wave imaging devices used in airports is projected to be 10,000-fold less than what is transmitted by cellular phones, according to information posted by the TSA.

The radiation: what it means for you

While the millimeter wave technology does not use x-ray, the backscatter scanners do. The x-ray used in these scanners is the same low-dose, ionizing radiation used in traditional x-rays. "These new backscatter devices are scanners that work by shooting a beam of x-ray at an individual," said Kenneth L. Andrews, a diagnostic radiological physicist for the West County Radiological Group at St. John's Mercy Health Care. "The device then measures what bounces back, using these very low energy x-rays to produce an image of the individual's anatomy. The purpose is to detect any explosive devices."

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The images are essentially a superficial outline of the body, said Andrews. "It creates an unclear picture but enables the viewer to see the shape of [an individual's body.]"

But, "depending on how the images are done, the resolution can be good," said William H. Perman, professor of medical physics and radiology at Saint Louis University. "The images can be quite detailed. It is a surface image of the body, essentially a virtual strip search. But I have not seen how well [a backscatter scanner] detects what we are concerned about: How well can it detect a powder bomb, for example?"

"These have been utilized as a secondary screening device, if there is any question, in lieu of a strip search," said Andrews. "[Officials] are now looking at these as a primary screening tool - this is what has raised the question of radiation dosages."

While the backscanner devices do use radiation, the amount of exposure associated with one of these scans is negligible, say Duncan, Andrews and Perman. "It is the equivalent of what a passenger would receive 2 to 4 minutes into a flight at 30,000 feet," according to Andrews. Duncan agreed, "You would get much more radiation from the plane ride than from these scanners," due to solar radiation exposure at high altitudes, he said.

Special populations

The TSA states on its Website that "passengers with joint replacements or other medical devices that would regularly alarm a metal detector often prefer this technology because it is quicker and less-invasive than a pat down."

While it is possible that radiofrequency energy (used in the millimeter wave technology) could provide interference with some medical devices, according to Andrews, the backscatter devices create no such concern. "There would be no interference from the x-ray," said Perman.

Radiation exposure is always a concern for pregnant women. "Fetuses are the most radiosensitive," said Perman, "but [they] would not be affected by these doses. The radiation risk is minimal -if not non-existent- even for frequent flyers."

"Even if you flew 35 times a year…so what?" proposed Perman. "That's one chest x-ray or even less."

Duncan concludes that any potential risks of screening are small. He puts it in perspective: "The riskiest part of flying is the drive to the airport."