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Science. Communication. Community.

Airport Security’s X-ray Vision

The two types of full body scanners used at airports differ in their imaging methods and radiation levels, but clear data on their health effects and safety are lacking.

by Amanda Alvarez

Nothing to see here. Image via Wikimedia Commons.

On a recent flight out of Boston Logan Airport, I opted out of the full body security scan. This was not the first time I’ve received the alternative pat down, and it was also not the first time I’d heard this quip from a TSA agent: “These are our new scanners, they don’t have radiation.” Was this, I wondered, ignorance on the part of the agents, new propaganda, or actual fact? Some kind of radiation must be involved; how else would the naked images of travelers be generated? To educate myself on the matter, I did some Googling.

The scanners at Boston Logan are the ProVision ATD model by L-3. Here’s how they work. High frequency radio waves bounce off the dense body but go through the flimsy clothing covering it, and an image is generated. These are millimeter wave scanners, which do use radiation, albeit of the non-ionizing variety. This kind of scanner is newer and not very well studied, thanks to TSA restrictions. While millimeter waves scanners don’t appear to be genotoxic (damaging to DNA), they are also ironically unable to detect potential threats like chemicals or light plastics. The TSA’s explanation of the safety of “advanced imaging technology” scanners is predictably vague.

Going through the other type of scanner, backscatter, is like receiving a full-body X-ray. One review estimated that, across all 750 million plane trips taken per year, six cancer cases could result from backscatter scans. While the radiation dose from a backscatter scanner is lower than that received in routine medical contexts – 50 airport scans equal one dental X-ray – there has been speculation that the doses could be much higher, with as many as 100 cases of cancer annually attributable to these scanners. As with any mechanical technology, scanners could also fail or go haywire, spitting out random higher doses by accident. While the incidental risk to the individual appears low, we don’t really know yet how these effects can compound.

The case remains that flying itself is more harmful than any security scan: a passenger on a long-haul, high-altitude flight is exposed to 4-5 microSieverts per hour. The allowable amount of radiation during a single airport security scan is one-sixteenth this amount, or 0.25 μSv. However, with more air passengers and more scanners being rolled out, a vast experiment with brief, high intensity pulses of radiation is being carried out, the effects of which may not be apparent for decades to come. The Indian nuclear regulator, for example, has not allowed backscatter scanners to be installed at that country’s airports, though it OKed millimeter wave scanners. In the US, airport scanners are not subject to the same regulatory oversight as medical devices, and haven’t been thoroughly tested; there is evidence the health risks associated with the scanners were downplayed when they were first introduced. I feel inclined to share the concern of the group of UC San Francisco scientists who urged the White House that more independent evaluation of the scanners is needed. In the meantime, though, I’ll probably keep flying.

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3 comments on “Airport Security’s X-ray Vision

  1. Jonathan
    April 10, 2013

    This was an interesting read, however, I wanted to clarify a statement that you made regarding mechanical failure of the x-ray system. To say that the scanner can “spit out random higher doses by accident” is not technically true.

    X-ray creation involves accelerating electrons across a vacuum from a cathode to a anode (x-ray source) which then generates the X-ray. The maximum energy that an x-ray can have is dependent upon the voltage applied to the tube. Most commercial scanners are operated in the 50 kVp (50,000 volts) range meaning the most powerful x-rays that system could produce are 50 keV. So yes, the x-ray tube could theoretically spit out x-rays with random amounts of energy, albeit all less than 50keV. This happens and is called Bremsstrahlung radiation. But the majority of x-rays are at specific characteristic energy peaks of the material used for the anode. There are safeguards in place to ensure a maximum voltage including voltage limiting circuits, etc.

    The real potential issue is not sporadic high energy radiation but a fault which would result in more of the SAME energy photons being concentrated at the same point on the skin. This would result in a local increase when computing the dose. This is still an unlikely event due to the relatively even distribution caused by an angled anode.

    So it is alarmist to claim that an x-ray system can go “haywire”. It makes me think of Robocop turned bad. Rather it is possible for the distribution of x-rays across the field of view to become slightly skewed resulting in locally increased radiation dose. Thanks to the low energy x-rays produced combined with the limitations of how widely this distribution can vary, this is still a relatively small change in radiation dose.

    None of this is to say that I like the idea of jumping into a back-scatter machine. I just think that, as scientists, we have to be careful in how we discuss technology that people may interact with regularly. You don’t want your grandmother refusing a hip x-ray because of an irrational fear of haywire machines.

    • neuroamanda
      April 10, 2013

      Thanks for the clarification, you’re absolutely right. I did mean to say that the radiation dose could become locally concentrated, but somehow ended up glossing this over with “haywire,” which admittedly does sound a little alarmist.

  2. Pingback: Leaving Vegas | life and breath: outliving lung cancer

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This entry was posted on April 9, 2013 by in Health, Policy, Uncategorized and tagged , , .
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