What is the radiation exposure from full-body scans used for airport security screening?

There are 2 types of full-body scanner machines that use "weak" X-rays and radio waves respectively:

- Backscatter radiation X-ray full-body scanners. The image looks like a chalk drawing (shown right).

- "Millimeter wave" (radio wave) full-body scanners. The image looks like a fuzzy photo negative.

Backscatter radiation X-ray full-body scanners

The older type of full-body scanners use so-called backscatter radiation to scan the entire body to detect foreign objects. Passengers will be directed to stand against a refrigerator-size backscatter machine as a "pencil-thin" X-ray beam rapidly scans them to produce textured "charcoal outlines" of their bodies. The backscatter uses a narrow, low-intensity X-ray beam that scans the entire body at a high speed. The X-ray is not strong enough to penetrate much beyond the skin, so it cannot find weapons that may be hidden in body cavities.

The amount of radiation used during this scan is equal to 15 minutes of exposure to natural background radiation such as the sun's rays. One scan emits less than 10 microrem, the unit used to measure radiation. Comparably, an hour on an airplane at a high altitude exposes a passenger to 300 microrem, and the average person is exposed to 1,000 microrem of radiation over the course of a normal day.

Thirty hours of airplane travel is the equivalent of one chest X-ray (CXR) - an important health warning for frequent flyers.

A backscatter X-ray scan gives a person as much radiation as he or she would get from two minutes of flying in an airplane at 30,000 feet. A traveler would have to undergo more than a thousand scans in a year to equal one standard chest X-ray.

Dr. Albert J. Fornace Jr., an expert in molecular oncology at Georgetown University Medical Center, said such a low dose was inconsequential, even for pregnant women. “Obviously, no radiation is even better than even a very low level,” Dr. Fornace said. “But this is trivial.” But David J. Brenner, a professor of radiation oncology at Columbia University, said that even though the risk for any individual was extremely low, he would still avoid it.

"Millimeter wave" (radio wave) full-body scanners

The newer type of scanners, called a "millimeter wave" machine, doesn't use radiation. It uses electromagnetic waves to create an image based on energy reflected from the body. According to the TSA these devices deliver 10,000 times less energy than a person's cell phone.

The millimeter wave machine works like this: A person walks into a large portal that resembles a that resembles a glass elevator (9 feet tall and 6 feet wide), pauses and lifts his or her arms while the machine takes two scans using radio waves. The scans take 1.8 seconds, and it takes about a minute for the image to appear on a computer screen in a separate location.

Privacy concerns

The Transportation Security Administration (TSA) promises no one will see the revealing images except trained security agents staring at computer screens in a nearby room. The body scans will be deleted after 12 seconds.

Special “privacy” software intentionally blurs the image, creating an outline of a body that is clear enough to see a collarbone, bellybutton or weapon, but flattens details of revealing contours.

Lawyers for the American Civil Liberties Union (ACLU) have raised objections, calling the X-ray scan a “virtual strip-search.”

References:

Airport Scanner Radiation Risks Are Minimal, Government Report Says - NYTimes, 2012.
TSA to Conduct New Study on Safety of X-Ray Body Scanners http://goo.gl/r6Kfl
Dutch to use full body scans for U.S. flights. CNN.
New Airport X-Rays Scan Bodies, Not Just Bags. NYT.
For their eyes only? Boston Globe.
Manufacturer says full body scanners at airports are a valuable tool in fighting terror. The Plain Dealer.
Body-scan machine eyed for airports. AP.
Manchester airport trials naked-image security scans. Guardian.
Radiation risk low with whole-body airport scanners. Reuters, 2010.
New Airport Scanners: Radiation Risk Tiny. WebMD, 2010.
Image source: Wikipedia, backscatter X-ray, US Transportation Security Administration part of U.S. Department of Homeland Security, public domain.

Read more on a Kindle:

26 comments:

  1. The discussions about radiation exposure are misleading. I suspect the manufacturers of these devices must have incredible power at squelching health concerns. We now know that exposure dangers may be a factor not only of levels but of how quickly you receive the dose. Your reasoning could also apply to a blow torch if its effects were not so immediate and obvious. "The blow torch won't burn you because you are exposed to the same (amount) of heat energy over a few hours of a warm day." Begin the torching of the masses? No level of exposure is safe!

    ReplyDelete
  2. John,

    I don't think the discussion is misleading. The blog post does not make any claims but simply quotes some of the leading experts in the field.

    Comparing blow torch to X-ray however can be misleading from a scientific perspective.

    ReplyDelete
  3. More importantly, how does the millimeter wave scanners (which use electromagnetic wave) affect a pacemaker? We're warned to stay away from metal detectors and hand wands because the magnets involved can affect a pacemaker.

    ReplyDelete
  4. John is correct, these discussions need to be placed in context, and the blog does not merely quote experts. His analogy is also correct, although that does not mean that the technology is dangerous, merely that it is not enough simply to look at total energy output. A person's history of exposure is also relevant, but that applies to air travellers generally (as the blog aptly points out).

    It is also misleading to state that 'a "millimeter wave" machine, doesn't use radiation. It uses electromagnetic waves'. X-Rays are also electromagnetic waves, as is all light. There is no mention of the health effects of millimeter wave machines, but it has been known for a long time that exposure to powerful radio sources can be dangerous, and there is some evidence that weak radio sources may have health implications, but this is not proven. This may not be a very powerful radio source, but we should know.

    Air travel will always be more dangerous than a scan, but that's not the point.

    ReplyDelete
  5. Re: "It is also misleading to state that 'a "millimeter wave" machine, doesn't use radiation."

    You can't be serious.

    How do you measure the radiation induced by radio waves then?

    ReplyDelete
  6. Who said that the rays of the sun are the same as radiowaves? The same people who think H2O is water, refined sugar is the same as natural sugar, mineral iron is the same as the iron in plants (and therefore mineral supplement iron is the same as plant supplement iron)... Don't you think there's a bit of a convenient assumption going on here?

    ReplyDelete
  7. "The same people who think H2O is water, refined sugar is the same as natural sugar..."

    --

    I'm not sure I get your point....

    ReplyDelete
  8. "millimeter wave" machine, doesn't use radiation. It uses electromagnetic waves" - the author should done their homework before writing this, all radiation is electromagnetic waves! Should have said this is non-ionizing radiation.

    ReplyDelete
  9. If 10uRem is the radiation exposure from a single scan, this is a very low and safe level. How do we know each machine is emitting the same amount of radiation? How do we know the machine is working correctly? I would like to know what the maximum radiation exposure would be if the machine is not working as intended. Then I would decide if the benefits outweigh the risk...

    What if the traveller moves (cough, sneeze, parkinsons) during the scan? Does it have to be repeated? How many times can a "screener" repeat the scan before considering radiation exposure?

    I doubt the "screeners" have the technical ability to perform QC on scanning/Xray equipment to ensure public safety. Unless there is a CHP or other radiation professional analyzing the QC data count me out! I'll take my chances in the pat down line

    ReplyDelete
  10. Re: "It uses electromagnetic waves" - the author should done their homework before writing this, all radiation is electromagnetic waves!"

    Good joke :)

    Of course, all Electromagnetic waves = Electromagnetic radiation. It's the same with heat radiation, even body heat radiation.

    This is not what we usually have in mind when we talk about radiation, of course.

    Just check Wikipedia for a start before posting comments:

    http://en.wikipedia.org/wiki/Electromagnetic_radiation

    http://en.wikipedia.org/wiki/Thermal_radiation

    ReplyDelete
  11. My background is in medical radiations. Radiation workers are provided with radiation monitors to wear that detect exposure to X and gamma rays. Whilst the damage caused by this type of ionising radiation is instantaneous, the longer term effects are unpredictable. Scattered radiation from an x-ray is considered to be quite destructive to both image quality and cellular health, which is why patients in hospitals who are exposed to frequent x-rays (e.g. intensive care, daily chest x-rays for weeks) should be covered with lead to absorb the scatter before it reaches organs outside the field of view, such as the gonads. Now with that in mind, if you travel frequently between cities (I have a brother who flies between two cities within Europe almost weekly), I would be concerned about the amount of cellular damage to skin, subcutaneous tissues and testes by such regular ionising exposure. It will be interesting to see if skin cancers increase if this technology becomes the norm.

    Radio-frequency exposure is measured as both estimated and total specific absorption rates (SAR), as used for MRI scans. (When talking about portion of the electromagnetic spectrum, the actual exposure and that absorbed by the body are different.) Pregnant women may undergo an MRI, but are generally advised that if they can wait beyond the first trimester, that this is preferable. Pregnant staff are advised not to remain in the scan room during image acquisition (when the RF is on). I do not allow my pregnant staff to remain in the room during scanning. I would not do so myself.

    Patients with pacemakers have been known to encounter problems with RF units at shop entrances and I would expect that the same could be expected for a small number with the millimeter wave scanners. Just as an aside, there are many other electronic devices implanted in patients for all manner of disorders that are not dissimilar to pacemakers (Deep brain stimulators for Parkinson's is an example, although I've not heard of issues with them). If you are not pregnant and don't have a electronically operated device implanted somewhere in your body, I see no problem with this scanner. I'd readily do so at any airport. But then I have the advantage of a very informed perspective, something the general public do not.

    ReplyDelete
  12. Thank you for your excellent comment, Watershedd!

    ReplyDelete
  13. Wait. Aren't cellphones being investigated as a link to brain cancer because of the RF exposure?

    It will be interesting to see if skin cancers increase if this technology becomes the norm.

    And isn't there some concern that sunscreen ingredients might be converting to free radicals when exposed to radiation? Or being a catalyst, in the case of micronized titanium dioxide.

    ReplyDelete
  14. "Aren't cellphones being investigated as a link to brain cancer because of the RF exposure?"

    No evidence in the current studies.

    "And isn't there some concern that sunscreen ingredients might be converting to free radicals when exposed to radiation?"

    There was something like that in the news a few months ago. Nothing definitive though.

    ReplyDelete
  15. What would a wet menstual pad look like? What would a colostomy bag look like? I see the potential for a lot of embarrassing time-wasting body searches. Meanwhile the terrorists will hide explosives in body cavities, fly on domestic flights, and detonate in the first hour of the flight.

    ReplyDelete
  16. isn't an easier and cheaper solution to all of this a trained dog at the airport?

    ReplyDelete
  17. "isn't an easier and cheaper solution to all of this a trained dog at the airport?"

    No.

    ReplyDelete
  18. "I'll take my chances in the pat down line"
    lucky for you that there may still be one where you live, in a lot of airports it is now mandatory to use the scan and you cannot board a flight without one all because of the oh so perfectly timed incident with the man who somehow...i repeat SOMEHOW GOT ON BOARD AN AIRPLANE WITH FIRECRACKERS IN HIS UNDERWEAR, this is impossible and as a result the ridiculous, insulting, and ludacris solution of naked body scans have been enacted. Which i remind you can cause skin cancer and there are now websites up that somehow got a hold of some of the images and now use them on there sites for "entertainment". i call that a violation of privacy and some would go as far to even call it unconstitutional. i think these scans are bull and need to be taken out of airports. i also think if the airlines don't to listen and decide to keep them, like some are doing now, then we should boycott. sell your stocks in there company until it either forces them to get rid of the scans or they will go bankrupt. Either way i feel it would be better for everybody to not worry about whether some creep is saving a picture of there naked body or if they are going to get skin cancer every time they need to go to the airport.

    ReplyDelete
  19. "But then I have the advantage of a very informed perspective, something the general public do not."

    and you say you work with radiation for a living? well then you of all people should know that radiation doses grow to become more and more harmful and keep accumulating onto the last time you took in radiation. So if you decide to travel lets say from Hawaii to long island and then back and lets just assume your the average american in todays society so you probably dont have enough money to fly direct. How many flights are you going to have to get on to get there and back? how much radiation would that be to add to what you might already have? how can you say, as some sort of radiation worker, that these scans dont seem too harmful?

    ReplyDelete
  20. There is no ionizing (e.g. proven "harmful") radiation with "millimeter wave" (radio wave) full-body scanners...

    Go through those if you have a choice.

    ReplyDelete
  21. "... radiation doses grow to become more and more harmful and keep accumulating ..."

    Ionising radiation from an external source (e.g. CT, x-ray machine) does not remain in the body for minutes, hours or days and hence, there is not cumulative dose. The energy is transferred to a cellular electron where it has an immediate effect. The measured cumulative exposure over a lifetime is a different thing. Particles that emit ionising radiation that are ingested, inhaled or injected (e.g. nuclear medicine bone scan using technetium, treatment for a thyroid disorder using an iodine isotope) decay over time, usually a matter of hours.

    The effects of externally created and delivered ionising radiation, such as that from a CT or x-ray machine are immediate. It is the cellular damage (and death) due to ionising radiation is cumulative. Hope this clarifies things.

    ReplyDelete
  22. "it is the cellular damage (and death) due to ionising radiation [that] is cumulative."

    Yes, indeed. But what you are saying is that the risk is cumulative.

    ReplyDelete
  23. I will refuse any form of radiation scanning at an airport. I have had enough X-rays and radio waves that I could not avoid. If they want to pull me into a room to search, so be it. If they demand I be scanned or I cannot fly, then I will never fly again.

    ReplyDelete
  24. This may be a document worth reviewing...

    http://dels.nas.edu/dels/rpt_briefs/beir_vii_final.pdf

    So if you take the dose from a single scan, convert the dose to risk (cancer mortality relative to dose, assuming LNT), then multiply that by the number of times people will be scanned, then you get an estimate of the mortality related to a program like this. I don't know. What about populations like pilots and crew, airport workers (scanned daily? 5 times/week? 50 weeks/year?), and frequent flyers?

    ReplyDelete
  25. This is my experience this Spring at Tampa airport. Inspite of my request for patdown/body search (since I have been exposed to many medical xrays of the years) I was scanned with the new airport scanner.

    When sat in my seat about 1/2 hour later I noticed that I could not focus on text in the safety pamphlet.

    On the way to the airport I read the map as a navigator in the rent-a-car as my husband drove.
    The inability to get full focus while reading lasted full 24hours , while my body craved chewable vitamin C with rutin...I found that a possible sideffect (cellular damage) could be to the capillaries - wonder if it happen to my eyes. I only use one eye for reading.

    I reported it to the flight attendant, because placating of the public is dime a dozen, but reports of adverse effects just a few.

    It took 43,000 dead people to pull Vioxx off the market...we need to know EVERY single adverse effect of the Frankenmachine.

    And speaking of the man with underware firecrackers - we watched on TV a couple who stood behind that man, and another man kept telling the security people that this young man
    "has to be on that plane inspite of NOT HAVING a passport." That couple on TV said they reported this to the FBI and were waiting to hear from the FBI. Wonder what does the FBI think about it, and the security people who let HIM on that plane...Now all of us are being subjected to unnecessary x-rays.

    ReplyDelete
  26. I am tired to hear just verbal assurances from numerous experts that "it is safe". They should release the actual physical values of radiation exposure. And we (sufficiently educated and intelligent American public) will determine if it is safe or not.

    Commenting on a "millimeter wave" scanners - they may appear to be even more dangerous. The ultra short wave length radio waves produce a ionizing radiation upon penetration into hard matter (human bones in this case). So radiation will be delivered as close as possible to the vital organs...

    ReplyDelete

Blog Widget by LinkWithin