Following the alleged failed bombing attempt on an Amsterdam to Detroit flight on Christmas Day, the use of full-body scanners at airport security in the United States has gained momentum as a more thorough method of screening passengers.
But some have expressed concerns about cumulative radiation exposure from the scans if they become more commonplace.
Still, most experts in radiation say the fears are unfounded.
The scanners being ordered by the government use a technology called backscatter x-rays, which deliver a low dose of "The backscatters have very, very low radiation," said Dr. James Thrall, chair of the American College of Radiology and chair of radiology at Massachusetts General Hospital in Boston. "Moreover, the individual x-rays themselves are very low energy, and unlike the x-ray spectrum that we use in medicine, the backscatter x-rays don't really penetrate to the organs in the body.
"When people hear the word x-ray, there's a natural concern," he said, but the exposure from the scanners is so low that "You would have to take hundreds and hundreds of trips requiring screening to even reach what would be considered a negligible dose."
A 2003 report from the National Council on Radiation Protection and Measurements estimated that 2,500 scans would be needed from full-body scanners in a year to exceed the suggested amount for a single radiation source.
The primary concerns for radiation exposure may be in cumulative exposure, but levels from a scan, although they may be an avoidable part of travel, are far below others a passenger will face on a flight.
For comparison, if, after a body scan, a passenger had four hours of flying and a two and a half hour layover in Denver, given the increased proximity to the sun from the high altitudes, the scan would be equal to about one seventieth of the overall radiation exposure.
"A conservative estimate of risk of death from additional cancers is 0.04 percent per rem," explained Dennis Mah, an associate professor and deputy director of physics at Montefiore Medical Center in New York.
Mah, estimates that would translate to 1.6 additional cases of cancer per 100 million people.
A rem refers to a standardized unit of radiation exposure.
"This is really small compared to the lifetime risk for cancer which is about one in three," he said. "Even if you are a frequent traveler this is not a big risk."
David J. Brenner, director of the Center for Radiological Research at the Columbia University Medical Center noted that some pregnant women may be concerned about entering a scanner with a fetus, given concerns about even the lowest levels of radiation. He also noted that the calculated risks are so small they may be theoretical, but said they only become a concern with a large enough population.
"The risks are small, but they are there," he said. "And if you multiply these risk by a billion scans a year, that becomes a significant risk."
Because the full-body scans involve radiation, some considerations do need to be taken, experts said.
David A. Schauer, executive director of the National Council on Radiation Protection and Measurements said that a comparable benefit would be needed to justify the radiation exposure involved.
But, he said, he believes these machines do just that.
"In the area of airline travel," said Schauer, "the benefit is shared by travelers, the air crew and the broader society."