[ed. Just noticed today, TSA is backing away from an independent study to evaluate the health effects of scanners, relying instead on draft conclusions from the Inspector General of Homeland Security.]
by Erica Swallow, Mashable
The first full body scanner was developed by Dr. Steven W. Smith, inventor of the Secure 1000 whole body scanner in 1992. Smith sold the scanner and associated patents to Rapiscan Systems, who now manufactures and distributes the device. Rapiscan is just one of three companies that manufacture commercial X-ray devices used as security scanning applications — the other two companies are Tek84 and American Science and Engineering.
If you’ve flown with a commercial airline in the past two years, you’ve probably encountered or heard news of full body scanners, which use either X-rays or millimeter radio waves to create a virtually nude image of a person’s body to identify any hidden objects, such as weapons or explosives, that the person may have concealed.
David J. Brenner, the Higgins Professor of Radiation Biophysics at Columbia University, explained quite simply in an interview with NPR late last year that “both [scanning technologies] work on the same basic principle of firing a beam of radiation at the individual and looking at what it’s reflected back, quite similar to radar or sonar, but in one case using millimeter waves, which are not so different from microwaves, in fact, and the other uses X-rays.”
Inventor Steven W. Smith explains backscatter X-ray scanning quite thoroughly in his 1993 patent for the technology behind the Secure 1000:
“A pencil beam of X-rays is scanned over the surface of the body of a person being examined. X-rays that are scattered or reflected from the subject’s body are detected by a detector. The signal produced by this scattered X-ray detector in then used to modulate an image display device to produce an image of the subject and any concealed objects carried by the subject.”Each pixel in the processed image is determined by the intensity of the backscattered signal collected by the X-ray detector. Because heavy elements (like most metals) backscatter electrons more strongly than light elements (such as tissue, organic materials and plastics), they show up differently in the processed images. With current technologies, heavy elements show up darker, while light elements appear brighter — as a result, concealed weapons, which are often made of heavy elements, can be detected.
Millimeter wave scanning works in the same way, except it uses millimeter waves instead of X-rays. The basic difference between the two technologies is that millimeter wave radiation — unlike high frequency X-rays — is not genotoxic and cannot cause cancer.
Safety Concerns
So, what does the proliferation of these scanners mean for the safety of travelers undergoing full-body scanning?
Backscatter X-ray scanning has received the majority of attention when it comes to safety issues, because “as far as we know, there is no health hazard associated with the millimeter wave scanners,” Dr. Brenner told NPR. On the other hand, he notes, “We know that X-rays can damage DNA in cells, and we know that X-rays can ultimately produce cancer. So the concern is about the possibility of inducing X-ray-induced cancer in one of the individuals who’s scanned.”
No conclusive studies have been conducted that confirm that backscatter X-ray security scanners are safe for commercial use. Advocates for the use of the scanners believe that low-energy X-rays are of negligible risk to scanned travelers, but researchers protest that even very small doses of ionizing radiation is carcinogenic. The health effects of backscatter X-ray scanning remain under scrutiny, especially in scientific communities focused on cancer and imaging.
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Image courtesy of iStockphoto, Marchcattle
