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This file combination of images taken on October 13, 2009 shows an airport staff member demonstrating a full body scan at Manchester Airport in Manchester, northwest England, and a computer screen showing the results of a full body scan.

Paul Ellis/AFP/Getty Images

Many Canadians have been caught up with worry this week that they might be forced to reveal much more than they want when passing through airport security.

But experts say concerns over new full-body scanners being installed in airports around the world extend beyond privacy issues.

Some types of full-body scanners use X-ray technology to generate an image - technology that emits radiation.

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Many experts agree that radiation from full-body scanners is likely to be at low, safe levels that won't cause serious harm to those passing through them. But some say that not enough is known about how much radiation passengers could be exposed to, and whether it could have any long-term effects on the population.

Those concerns are prompting new questions over whether certain groups, including frequent fliers, pilots and other airline workers, face heightened risk as a result of repeated scans.

"I don't think the right questions have been asked," said Douglas Boreham, professor in medical physics and applied radiation sciences at McMaster University in Hamilton, Ont. "We don't have enough information to make a decision on whether there's going to be a biological effect or not."

Transport Canada announced this week that full-body scanners would be installed at a handful of major Canadian airports starting this month, following a similar move in the United States in response to an attempted terrorist attack on a flight that land in Detroit on Christmas Day.

More than 40 scanners will be installed in airports in Vancouver, Calgary, Edmonton, Winnipeg, Toronto, Ottawa, Montreal and Halifax.

All of the scanners used in Canadian airports will use "millimetre wave" technology, or radio frequency waves, to produce a three-dimensional image of a person's body in order to detect hidden objects, such as weapons or explosives. Radio wave technology doesn't pose the health concerns of ionizing radiation.

Some full-body scanners in the United States, however, will use X-ray technology to generate images. Called backscatter, the technology involves the use of low-level X-rays to create back and front images. Canadians passing through U.S. airports may be subject to X-ray scanners.

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X-rays expose patients to ionizing radiation, which can have enough energy to displace electrons from an atom. In patients, ionizing radiation can enter cells and ionize, or create a positive charge, in molecules, potentially leading to changes or mutations that could be harmful.

But the potential risks depend on the dose and amount of time patients are exposed to ionizing radiation.

Air security officials say the radiation levels used in X-ray body scanners are very low, a sentiment echoed by many radiology experts.

"I would say it's minimal concern," said James Hevezi, chair of the medical physics commission of the American College of Radiology.

"The kind of doses are extremely low compared to, say, the kind of exposure the flying public will have at the altitude that the plane is flying in." At high altitudes, passengers are exposed to elevated levels of cosmic radiation from space.

However, Dr. Boreham said radiation from X-ray scanners may be more concentrated and have a different biological effect than radiation that occurs naturally at high altitudes. That's one of the many reasons the potential effects of X-ray scanners should be scrutinized, he said.

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Dr. Boreham said there is a small chance that frequent fliers or individuals sensitive to the effects of radiation could face a risk. The problem is that officials haven't said how much radiation the scanners will emit.

While government officials say the radiation will be at safe, low levels, Dr. Boreham said research should be done to investigate how the scanners could affect people in real-world scenarios.

"There should be concern if someone hasn't looked at this yet," Dr. Boreham said.

In Canada, all passengers travelling to the United States are currently subject to secondary screening, which will soon include scans by the new machines. But Canadian officials said passengers could choose to have a manual pat-down by officials instead of the security scan.

The machines could also be used to scan other passengers, regardless of their destination, said a Transport Canada spokeswoman.

Although the scanners have sparked a heated debate over privacy issues, Canadian officials say the images will be reviewed by a screening officer in a separate room and won't contain any identifying features.

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