Backscatter X-ray
Encyclopedia
Backscatter X-ray is an advanced X-ray
imaging
technology. Traditional X-ray machine
s detect hard and soft materials by the variation in transmission through the target. In contrast, backscatter X-ray detects the radiation that reflects
from the target. It has potential applications where less-destructive examination is required, and can be used if only one side of the target is available for examination.
The technology is one of two types of whole body imaging technologies being used to perform full-body scans of airline passengers to detect hidden weapons, tools, liquids, narcotics, currency, and other contraband. A competing technology is millimeter wave scanner
. These airport security machines are also referred to as "body scanner", "whole body imager (WBI)", and "security scanner".
effect of X-rays, a form of ionizing radiation
. Unlike a traditional X-ray machine which relies on the transmission of X-rays through the object, backscatter X-ray detects the radiation that reflects from the object and forms an image. The backscatter pattern is dependent on the material property, and is good for imaging organic material.
In contrast to millimeter wave scanner
s which create a 3D image, backscatter X-ray scanners will typically only create a 2D image. For airport screening, images are taken from both sides of the human body.
Backscatter X-ray was first applied in a commercial low dose personnel scanning system by Dr. Steven W. Smith. Dr. Smith developed the Secure 1000 whole body scanner in 1992 and then sold the device and associated patents to Rapiscan Systems who now manufactures and distributes the device.
The following companies manufacture commercial X-ray devices that are used in security scanning applications with price ranging from $500,000 to $2,000,000:
The "Z Backscatter Van", or ZBV, from AS&E is a mobile backscatter X-ray machine in a van which "from the outside looks like an ordinary delivery van, allowing it to blend in to urban and other landscapes". It is being promoted as a means of examining the contents of vehicles, containers, and dumpsters. Like many of the truck-based scanners, it has an 'arm' that deploys from the van to be able to scan other vehicles passing through.
Other companies in the industry are Smiths Detection and Rapiscan.
There are also gamma-ray based systems coming to market, like the MVACIS.
In May 2011, the Electronic Privacy Information Center filed suit against DHS under the Freedom of Information Act, claiming that DHS had withheld nearly 1000 pages of documents related to the Z backscatter vans and other mobile backscatter devices.
Backscatter x-ray technology has been proposed as an alternative to personal searches at airport and other security checkpoints easily penetrating clothing to reveal concealed weapons. It raises privacy concerns about what is seen by the person viewing the scan. Some worry that viewing the image violates confidential medical information, such as the fact a passenger uses a colostomy bag, has a missing limb or wears a prosthesis, or is transsexual, despite the fact that the person viewing the image can't see the person they are screening.
The ACLU and the Electronic Privacy Information Center
are opposed to this use of the technology, currently in use in the U.S. at 78 airports, four court houses, and two correctional facilities, with another 12 airports scheduled to receive them soon. The ACLU refers to backscatter x-rays as a "virtual strip search". In one Transportation Security Administration
(TSA) trial, 79 percent of the public opted to try backscatter over the traditional pat-down in secondary screening.
It is "possible for backscatter X-raying to produce photo-quality images of what's going on beneath our clothes", thus, many software implementations of the scan have been designed to distort private areas. According to the TSA, further distortion is used in the Phoenix airport's trial system where photo-quality images are replaced by chalk outlines. The TSA has also commented that screening procedures such as having the screener viewing the image located far away from the person being screened could be a possibility.
In light of this, some journalists have expressed concern that this blurring may allow people to carry weapons or certain explosives aboard by attaching the object or substance to their genitals.
The British newspaper The Guardian
has revealed concern among British officials that the use of such scanners to scan children may be illegal under the Protection of Children Act 1978
, which prohibits the creation and distribution of indecent images of children. This concern may delay the introduction of routine backscatter scanning in UK airports, which had been planned in response to the attempted Christmas Day 2009 attack on Northwest Airlines Flight 253
.
The Fiqh Council of North America
have also issued the following fatwa
:
In August 2010, it was reported that U.S. Marshals (part of the Department of Justice), saved thousands of images from a low resolution MM wave scanner
: This machine does not show details of human anatomy, and is a different kind of machine than the one used in airports. TSA, part of the Department of Homeland Security, reiterated that its scanners do not save images and that the scanners do not have the capability to save images when they are installed in airports. In contrast, it is claimed that TSA officials admitted that the scanners are required to be capable of saving images for the purpose of evaluation, training and testing.
TSA states that independent polling indicates that the U.S. public generally supports the deployment and use of body scanners at airports.
The next generation of backscatter scanners are able to screen these types of clothing. The next generation of scanners can equalize the screening process for all persons so that religious majorities can travel through the imaging process as easily as other passengers.
that damages chemical bonds. Ionizing radiation is considered carcinogenic even in very small doses
but at the doses used in airport scanners this effect is believed to be negligible for an individual. If 1 million people were exposed to 520 scans in one year, one study estimated that roughly four additional cancers would occur due to the scanner, in contrast to the 600 additional cancers that would occur from the higher levels of radiation during flight.
Since the scanners do not have a medical purpose, the United States Food and Drug Administration
(FDA) does not need to subject them to the same safety evaluations as medical X-rays. However, the FDA has created a webpage comparing known estimates of the radiation from backscatter X-ray body scanners to that of other known sources. The web site states that:
Four professors at the University of California, San Francisco
, among them members of NAS and an expert in cancer and imaging, in a April 2010 letter to the presidential science and technology advisor
raised several concerns about the validity of the indirect comparisons the Food and Drug Administration
used in evaluating the safety of backscatter x-ray machines. They argued that the effective dose is higher than claimed by the TSA and the body scanner manufacturers because the dose was calculated as if distributed throughout the whole body whereas the most of the radiation is absorbed in the skin and tissues immediately underneath. Other professors from the radiology department at UCSF disagree with the claims of the signing four professors.
The UCSF experts requested that additional data be made public detailing the specific data regarding sensitive areas such as the skin and certain organs, as well as data on the special (high risk) population. In October 2010, the FDA and TSA responded to these concerns. The letter cites reports which show that the specific dose to the skin is some 89,000 times lower than the annual limit to the skin established by the NCRP
. Regarding the UCSF concerns over the high risk population to sensitive organs, the letter states that such an individual "would have to receive more than 1000 screenings to begin to approach the annual limit".
John Sedat, the principal author of the UCSF letter, responded in November 2010 that the White House's claim that full-body scanners pose no health risks to air travelers is in "error," adding that the White House statement has "many misconceptions, and we will write a careful answer pointing out their errors."
In a December 2, 2010 letter to the House of Representatives, Dr. Steven Smith, inventor of the body scanner in 1991, has stated that the concerns of Dr. Brenner and UCSF regarding the skin dose of backscatter scanners is incorrect and the result of a confusion between dose and imaging penetration. Dr. Smith demonstrates this difference with two experiments using plastic (with a similar rate of absorption
as body tissue), copper (the image subject), and an x-ray scanner. The dose penetration experiment shows that 5mm and 50mm plastic samples absorb 5% and 50% of the beam intensity respectively, whereas the imaging penetration experiment shows that 4.8mm and 10mm plastic samples reduce the image darkness by 23% and 50% respectively. Dr. Smith states that those who calculate high skin dosage have incorrectly used the shallow imaging penetration value of a few millimeters whereas the actual dosage is calculated by the deeper dose penetration.
The TSA has also made public various independent safety assessments of the Secure 1000 Backscatter X-ray Scanner.
Radiation safety authorities including the National Council on Radiation Protection and Measurements
, The Health Physics Society and the American College of Radiology
, have stated that there is no specific evidence that full-body scans are unsafe. The Secure 1000 Backscatter X-ray scanner was developed in 1992 by Dr. Steve Smith. The scanner has been studied extensively for almost 20 years by the leading independent radiation safety authorities in the United States. Experimental and epidemiological data do not support the proposition, however, that there is a threshold dose of radiation below which there is no increased risk of cancer.
The UK Health Protection Agency has completed an analysis of the X-ray dose from backscatter scanners and has written that the dose is extremely low and "about the same as people receive from background radiation in an hour".
The Health Physics Society (HPS) reports that a person undergoing a backscatter scan receives approximately 0.05 μSv
(or 0.005 mrems
) of radiation; American Science and Engineering Inc. reports 0.09 μSv (0.009 mrems). At the high altitudes typical of commercial flights, naturally occurring cosmic radiation is considerably higher than at ground level. The radiation dose for a six hour flight is 20 μSv (2 mrems) — 200 to 400 times larger than a backscatter scan. According to U.S. regulatory agencies, "1 mrem per year is a negligible dose of radiation, and 25 mrem per year from a single source is the upper limit of safe radiation exposure".
According to a draft standard on the United States FDA website, the allowable dose from a scan would be 0.1 μSv, and that report uses a model whereby a 0.01 μSv dose increases an individual's risk of death by cancer during his or her lifetime by . Since the dose limit is ten times higher than 0.01 μSv, their model would predict one additional cancer death per 200 million scans. Since the airports in the UK handled 218 million passengers in 2009, if all passengers in the UK were scanned at the maximum dosage, then each year this would produce on average one additional cancer death (since there would be 200 million scans per year that the scanners were in operation), though usually each death would not occur in the same year as the particular scan that caused it, since the cancer may take years to grow. In addition, additional people would be given cancer but would die from other causes.
There may not yet be evidence of hereditory effects of x-rays administered by backscatter scanners, but backscatter scanners use the same kind of x-ray photons as are produced in medical x-ray machines but expose the subject at a considerably lower dose, so it is possible that the results from medical radiology may be relevant, at least until a study is done of any effects specific to backscatter x-ray machines. Fathers exposed to medical diagnostic x-rays are more likely to have infants who contract leukemia, especially if exposure is closer to conception or includes two or more X-rays of the lower gastrointestinal (GI) tract or lower abdomen. In medical radiography the x-ray beam is adjusted to expose only the area of which an image is required, so that generally shielding is applied to the patient to avoid exposing the gonads, whereas in an airport backscatter scan, the testicles of men and boys will be deliberately subjected to the direct beam in order to check for weapons in the underpants, and some radiation will also reach the ovaries of female subjects. Double - strand breaks in DNA of human sperm has been studied at very high x-ray doses in which they found a linear dose-response relationship at high doses. They did not study the effect at doses as low as would be used in x-ray airport scanners.
Extrapolations of cancer risk from minuscule exposures to radiation across large populations, however, are not supported by analysis by the National Council on Radiation Protection (NCRP). On May 26, 2010 NCRP issued a press release to address such comments about full body scanners that are compliant with ANSI N43.17. In Commentary No.16 issued on May 26, 2010, it reads as follows:
According to NCRP, the use of statistical extrapolations that predict 1 death for every 200 million persons scanned for example (as above) is an unrealistic over-estimation.
Other scientists at Columbia University have made the following statements in support of the safety of body scanners:
Furthermore, other scientists claim the health effects of backscatter are well understood whereas those from millimeter wave scanner
s are not:
Experts evaluating backscatter x-ray machine technology have also argued that defects in the machines, damage from normal wear-and-tear, or software errors could focus an intense dose of radiation on just one spot of the body. For example, Dr. Peter Rez, a professor of physics at Arizona State University, has said, "The thing that worries me the most, is not what happens if the machine works as advertised, but what happens if it doesn't," adding that a potential malfunction of the machine could increase the radiation dose.
The designers and manufacturers of backscatter X-ray scanners claim that the scanners are designed to prevent the occurrence of these kinds of errors. The scanners' safety requirements include fail-safe controls and multiple overlapping interlocks. These features, combined with fault analysis, ensure that failure of any subsystem results in non-operation of the x-ray generator to prevent accidental exposures. In the United States, the TSA requires that certification to the ANSI N43.17 safety standard is performed by a third party and not by the manufacturer themselves.
The European Commission
issued a report stating that backscatter x-ray scanners pose no known health risk, and that "assuming all other conditions equal", that backscatter x-ray scanners, which expose people to ionizing radiation, should not be used when millimeter-wave scanners that "have less effects on the human body" are available.
However, the European Commission report provides no data substantiating its claim that "all other conditions are equal". One area where backscatter X-ray scanners can provide better performance than MM wave scanners, for example, is in the inspection of the shoes, groin and armpit regions of the body.
In a study published in the Archives of Internal Medicine
on March 28, 2011 researchers at the University of California "calculated that fully implementing backscatter scanners would not significantly increase the lifetime risk of cancer for travelers." The researchers calculated that for every 100 million passengers who flew seven one-way flights, there would be one additional cancer.
In May 2011 several scientists, including Agard, Sedat, Shuman, and Stroud from UCSF, complained that TSA's testing of the scanners was inadequate, and that its safety research report was heavily redacted and based on a model of a scanner, not on an actual scanner. Peter Rez, of Arizona State, also worried about mechanical failures that could lead to overdoses.
In the US, an X-ray system can be considered to comply with requirements for general purpose security screening of humans if the device complies with American National Standards Institute (ANSI) Standard #N43.17.
In the most general sense, N43.17 states that a device can be used for general purpose security screening of humans if the dose to the subject is less than 25 μrems
(0.25 μSv
) per examination and complies with other requirements of the standard. Twenty-five micro Rem is equal to the amount of background radiation every human is exposed to (from the air and soil) at sea level every 1.5 hours and is also equal to the radiation exposure from cosmic rays when travelling in an airplane at altitude for 2 minutes.
Many types of X-ray systems can be designed to comply with ANSI N43.17 including transmission X-ray, backscatter X-ray and gamma ray systems. Not all backscatter X-ray devices necessarily comply with ANSI N43.17; only the manufacturer or end user can confirm compliance of a particular product to the standard.
ANSI standards use a standard of measurement algorithm called "effective dose" that considers the different exposure of all parts of the body and then weights them differently. The interior of the human body is given more weight in this survey and the exterior including the skin organ are given less weight. The Rapiscan
backscatter machine produces an X-ray more absorbed by the skin than most other X-ray devices but is still regulated under the ANSI. The standard for "effective dose" damage done to the skin by X-rays is similar to the damage done by sunlight. http://www.youtube.com/watch?v=eS0UxXDNs4w
The European Union is currently considering whether it is acceptable for this technology to be deployed in European Union
airports. A report is pending from the Transport Committee of the European Parliament
.
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
imaging
Medical imaging
Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
technology. Traditional X-ray machine
X-ray machine
An X-ray generator is a device used to generate X-rays. These devices are commonly used by radiographers to acquire an x-ray image of the inside of an object but they are also used in sterilization or fluorescence....
s detect hard and soft materials by the variation in transmission through the target. In contrast, backscatter X-ray detects the radiation that reflects
Backscatter
In physics, backscatter is the reflection of waves, particles, or signals back to the direction they came from. It is a diffuse reflection due to scattering, as opposed to specular reflection like a mirror...
from the target. It has potential applications where less-destructive examination is required, and can be used if only one side of the target is available for examination.
The technology is one of two types of whole body imaging technologies being used to perform full-body scans of airline passengers to detect hidden weapons, tools, liquids, narcotics, currency, and other contraband. A competing technology is millimeter wave scanner
Millimeter wave scanner
A millimeter wave scanner is a whole–body imaging device used for detecting objects concealed underneath a person’s clothing. Typical uses for this technology include detection of items for commercial loss prevention, smuggling and screening at government buildings and airport security...
. These airport security machines are also referred to as "body scanner", "whole body imager (WBI)", and "security scanner".
Technology
Backscatter technology is based on the X-ray compton scatteringCompton scattering
In physics, Compton scattering is a type of scattering that X-rays and gamma rays undergo in matter. The inelastic scattering of photons in matter results in a decrease in energy of an X-ray or gamma ray photon, called the Compton effect...
effect of X-rays, a form of ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
. Unlike a traditional X-ray machine which relies on the transmission of X-rays through the object, backscatter X-ray detects the radiation that reflects from the object and forms an image. The backscatter pattern is dependent on the material property, and is good for imaging organic material.
In contrast to millimeter wave scanner
Millimeter wave scanner
A millimeter wave scanner is a whole–body imaging device used for detecting objects concealed underneath a person’s clothing. Typical uses for this technology include detection of items for commercial loss prevention, smuggling and screening at government buildings and airport security...
s which create a 3D image, backscatter X-ray scanners will typically only create a 2D image. For airport screening, images are taken from both sides of the human body.
Backscatter X-ray was first applied in a commercial low dose personnel scanning system by Dr. Steven W. Smith. Dr. Smith developed the Secure 1000 whole body scanner in 1992 and then sold the device and associated patents to Rapiscan Systems who now manufactures and distributes the device.
The following companies manufacture commercial X-ray devices that are used in security scanning applications with price ranging from $500,000 to $2,000,000:
- American Science and EngineeringAmerican Science and EngineeringAmerican Science and Engineering Inc, is a US manufacturer of X-ray equipment and related technologies, originating in 1958 as a developer for NASA, with an early focus on X-ray astronomy led by Riccardo Giacconi...
(device name: Smartcheck) - Rapiscan SystemsRapiscan SystemsRapiscan Systems is a global privately held company that specializes in walk-through metal detectors, and x-ray machines for airport luggage and cargo screening...
(a subsidiary of OSI Systems Inc.) (device name: Secure 1000) - Tek84 (formerly Spectrum San Diego Inc.) (device name: AIT84 Body Scanner & Castscope)
Large scale
Some backscatter X-ray scanners can scan much larger objects, such as trucks and containers. This scan is much faster than a physical search, and could potentially allow a larger percentage of shipping to be checked for smuggled items, weapons, drugs, or people.The "Z Backscatter Van", or ZBV, from AS&E is a mobile backscatter X-ray machine in a van which "from the outside looks like an ordinary delivery van, allowing it to blend in to urban and other landscapes". It is being promoted as a means of examining the contents of vehicles, containers, and dumpsters. Like many of the truck-based scanners, it has an 'arm' that deploys from the van to be able to scan other vehicles passing through.
Other companies in the industry are Smiths Detection and Rapiscan.
There are also gamma-ray based systems coming to market, like the MVACIS.
In May 2011, the Electronic Privacy Information Center filed suit against DHS under the Freedom of Information Act, claiming that DHS had withheld nearly 1000 pages of documents related to the Z backscatter vans and other mobile backscatter devices.
Privacy
The ACLU and the Electronic Privacy Information Center
Electronic Privacy Information Center
Electronic Privacy Information Center is a public interest research group in Washington, D.C. It was established in 1994 to focus public attention on emerging civil liberties issues and to protect privacy, the First Amendment, and constitutional values in the information age...
are opposed to this use of the technology, currently in use in the U.S. at 78 airports, four court houses, and two correctional facilities, with another 12 airports scheduled to receive them soon. The ACLU refers to backscatter x-rays as a "virtual strip search". In one Transportation Security Administration
Transportation Security Administration
The Transportation Security Administration is an agency of the U.S. Department of Homeland Security that exercises authority over the safety and security of the traveling public in the United States....
(TSA) trial, 79 percent of the public opted to try backscatter over the traditional pat-down in secondary screening.
It is "possible for backscatter X-raying to produce photo-quality images of what's going on beneath our clothes", thus, many software implementations of the scan have been designed to distort private areas. According to the TSA, further distortion is used in the Phoenix airport's trial system where photo-quality images are replaced by chalk outlines. The TSA has also commented that screening procedures such as having the screener viewing the image located far away from the person being screened could be a possibility.
In light of this, some journalists have expressed concern that this blurring may allow people to carry weapons or certain explosives aboard by attaching the object or substance to their genitals.
The British newspaper The Guardian
The Guardian
The Guardian, formerly known as The Manchester Guardian , is a British national daily newspaper in the Berliner format...
has revealed concern among British officials that the use of such scanners to scan children may be illegal under the Protection of Children Act 1978
Protection of Children Act 1978
The Protection of Children Act 1978 is an Act of the Parliament of the United Kingdom.The Protection of Children Bill was put before Parliament as a Private Member's Bill by Cyril Townsend in the 1977-1978 session of Parliament....
, which prohibits the creation and distribution of indecent images of children. This concern may delay the introduction of routine backscatter scanning in UK airports, which had been planned in response to the attempted Christmas Day 2009 attack on Northwest Airlines Flight 253
Northwest Airlines Flight 253
Northwest Airlines Flight 253 was an international passenger flight from Amsterdam Airport Schiphol in Haarlemmermeer, Netherlands, to Detroit Metropolitan Wayne County Airport in Romulus, Michigan, United States...
.
The Fiqh Council of North America
Fiqh Council of North America
The Fiqh Council of North America is an association of Muslims who interpret Islamic law on the North American continent.Its 18 members issue religious rulings, resolve disputes, and answer questions relating to the Islamic faith...
have also issued the following fatwa
Fatwa
A fatwā in the Islamic faith is a juristic ruling concerning Islamic law issued by an Islamic scholar. In Sunni Islam any fatwā is non-binding, whereas in Shia Islam it could be considered by an individual as binding, depending on his or her relation to the scholar. The person who issues a fatwā...
:
In August 2010, it was reported that U.S. Marshals (part of the Department of Justice), saved thousands of images from a low resolution MM wave scanner
Millimeter wave scanner
A millimeter wave scanner is a whole–body imaging device used for detecting objects concealed underneath a person’s clothing. Typical uses for this technology include detection of items for commercial loss prevention, smuggling and screening at government buildings and airport security...
: This machine does not show details of human anatomy, and is a different kind of machine than the one used in airports. TSA, part of the Department of Homeland Security, reiterated that its scanners do not save images and that the scanners do not have the capability to save images when they are installed in airports. In contrast, it is claimed that TSA officials admitted that the scanners are required to be capable of saving images for the purpose of evaluation, training and testing.
TSA states that independent polling indicates that the U.S. public generally supports the deployment and use of body scanners at airports.
Equal treatment of minorities
Current backscatter scanners installed by the TSA are unable to screen adequately for security threats inside turbans, hijab, burqas, casts, prosthetics and loose clothing. This technology limitation of current scanners often requires these persons to undergo additional screening by hand or other methods and can cause additional delay or feelings of harassment.The next generation of backscatter scanners are able to screen these types of clothing. The next generation of scanners can equalize the screening process for all persons so that religious majorities can travel through the imaging process as easily as other passengers.
Health effects
Unlike cell phone signals, or millimeter-wave scanners, the energy being emitted by a backscatter X-ray is a type of ionizing radiationIonizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
that damages chemical bonds. Ionizing radiation is considered carcinogenic even in very small doses
Linear no-threshold model
The linear no-threshold model is a method for predicting the long term, biological damage caused by ionizing radiation and is based on the assumption that the risk is directly proportional to the dose at all dose levels....
but at the doses used in airport scanners this effect is believed to be negligible for an individual. If 1 million people were exposed to 520 scans in one year, one study estimated that roughly four additional cancers would occur due to the scanner, in contrast to the 600 additional cancers that would occur from the higher levels of radiation during flight.
Since the scanners do not have a medical purpose, the United States Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
(FDA) does not need to subject them to the same safety evaluations as medical X-rays. However, the FDA has created a webpage comparing known estimates of the radiation from backscatter X-ray body scanners to that of other known sources. The web site states that:
To put the radiation dose received into perspective:
- Naturally occurring ionizing radiation is all around us. We are continuously exposed to this background radiation during ordinary living. In 42 minutes of ordinary living, a person receives more radiation from naturally occurring sources than from screening with any general-use x-ray security system.
- The national radiation safety standard (see below) sets a dose per screening limit for the general-use category. To meet the requirements of the general-use category a full-body x-ray security system must deliver less than the dose a person receives during four minutes of airline flight. TSA has set their dose limit to ensure a person receives less radiation from one scan with a TSA general-use x-ray security system than from two minutes of airline flight.
- A person would have to be screened more than a thousand times in one year to exceed the annual radiation dose limit for people screening that has been set by expert radiation safety organizations.
Four professors at the University of California, San Francisco
University of California, San Francisco
The University of California, San Francisco is one of the world's leading centers of health sciences research, patient care, and education. UCSF's medical, pharmacy, dentistry, nursing, and graduate schools are among the top health science professional schools in the world...
, among them members of NAS and an expert in cancer and imaging, in a April 2010 letter to the presidential science and technology advisor
John Holdren
John Paul Holdren is advisor to President Barack Obama for Science and Technology, Director of the White House Office of Science and Technology Policy, and Co-Chair of the President’s Council of Advisors on Science and Technology...
raised several concerns about the validity of the indirect comparisons the Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
used in evaluating the safety of backscatter x-ray machines. They argued that the effective dose is higher than claimed by the TSA and the body scanner manufacturers because the dose was calculated as if distributed throughout the whole body whereas the most of the radiation is absorbed in the skin and tissues immediately underneath. Other professors from the radiology department at UCSF disagree with the claims of the signing four professors.
The UCSF experts requested that additional data be made public detailing the specific data regarding sensitive areas such as the skin and certain organs, as well as data on the special (high risk) population. In October 2010, the FDA and TSA responded to these concerns. The letter cites reports which show that the specific dose to the skin is some 89,000 times lower than the annual limit to the skin established by the NCRP
National Council on Radiation Protection and Measurements
The National Council on Radiation Protection and Measurements is a U.S. organization. It has a congressional charter under Title 36 of the United States Code, but this does not imply it has any sort of oversight or supervision from Congress; it is not a government entity.This text appears on the...
. Regarding the UCSF concerns over the high risk population to sensitive organs, the letter states that such an individual "would have to receive more than 1000 screenings to begin to approach the annual limit".
John Sedat, the principal author of the UCSF letter, responded in November 2010 that the White House's claim that full-body scanners pose no health risks to air travelers is in "error," adding that the White House statement has "many misconceptions, and we will write a careful answer pointing out their errors."
In a December 2, 2010 letter to the House of Representatives, Dr. Steven Smith, inventor of the body scanner in 1991, has stated that the concerns of Dr. Brenner and UCSF regarding the skin dose of backscatter scanners is incorrect and the result of a confusion between dose and imaging penetration. Dr. Smith demonstrates this difference with two experiments using plastic (with a similar rate of absorption
Attenuation coefficient
The attenuation coefficient is a quantity that characterizes how easily a material or medium can be penetrated by a beam of light, sound, particles, or other energy or matter. A large attenuation coefficient means that the beam is quickly "attenuated" as it passes through the medium, and a small...
as body tissue), copper (the image subject), and an x-ray scanner. The dose penetration experiment shows that 5mm and 50mm plastic samples absorb 5% and 50% of the beam intensity respectively, whereas the imaging penetration experiment shows that 4.8mm and 10mm plastic samples reduce the image darkness by 23% and 50% respectively. Dr. Smith states that those who calculate high skin dosage have incorrectly used the shallow imaging penetration value of a few millimeters whereas the actual dosage is calculated by the deeper dose penetration.
The TSA has also made public various independent safety assessments of the Secure 1000 Backscatter X-ray Scanner.
Radiation safety authorities including the National Council on Radiation Protection and Measurements
National Council on Radiation Protection and Measurements
The National Council on Radiation Protection and Measurements is a U.S. organization. It has a congressional charter under Title 36 of the United States Code, but this does not imply it has any sort of oversight or supervision from Congress; it is not a government entity.This text appears on the...
, The Health Physics Society and the American College of Radiology
American College of Radiology
The American College of Radiology , founded in 1923, is a non-profit professional medical association composed of diagnostic radiologists, radiation oncologists, interventional radiologists, nuclear medicine physicians, and medical physicists. It is based in Reston, Virginia, with offices in...
, have stated that there is no specific evidence that full-body scans are unsafe. The Secure 1000 Backscatter X-ray scanner was developed in 1992 by Dr. Steve Smith. The scanner has been studied extensively for almost 20 years by the leading independent radiation safety authorities in the United States. Experimental and epidemiological data do not support the proposition, however, that there is a threshold dose of radiation below which there is no increased risk of cancer.
The UK Health Protection Agency has completed an analysis of the X-ray dose from backscatter scanners and has written that the dose is extremely low and "about the same as people receive from background radiation in an hour".
The Health Physics Society (HPS) reports that a person undergoing a backscatter scan receives approximately 0.05 μSv
Sievert
The sievert is the International System of Units SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in gray...
(or 0.005 mrems
Röntgen equivalent man
Named after Wilhelm Röntgen , the roentgen equivalent in man or rem is a unit of radiation dose equivalent...
) of radiation; American Science and Engineering Inc. reports 0.09 μSv (0.009 mrems). At the high altitudes typical of commercial flights, naturally occurring cosmic radiation is considerably higher than at ground level. The radiation dose for a six hour flight is 20 μSv (2 mrems) — 200 to 400 times larger than a backscatter scan. According to U.S. regulatory agencies, "1 mrem per year is a negligible dose of radiation, and 25 mrem per year from a single source is the upper limit of safe radiation exposure".
According to a draft standard on the United States FDA website, the allowable dose from a scan would be 0.1 μSv, and that report uses a model whereby a 0.01 μSv dose increases an individual's risk of death by cancer during his or her lifetime by . Since the dose limit is ten times higher than 0.01 μSv, their model would predict one additional cancer death per 200 million scans. Since the airports in the UK handled 218 million passengers in 2009, if all passengers in the UK were scanned at the maximum dosage, then each year this would produce on average one additional cancer death (since there would be 200 million scans per year that the scanners were in operation), though usually each death would not occur in the same year as the particular scan that caused it, since the cancer may take years to grow. In addition, additional people would be given cancer but would die from other causes.
There may not yet be evidence of hereditory effects of x-rays administered by backscatter scanners, but backscatter scanners use the same kind of x-ray photons as are produced in medical x-ray machines but expose the subject at a considerably lower dose, so it is possible that the results from medical radiology may be relevant, at least until a study is done of any effects specific to backscatter x-ray machines. Fathers exposed to medical diagnostic x-rays are more likely to have infants who contract leukemia, especially if exposure is closer to conception or includes two or more X-rays of the lower gastrointestinal (GI) tract or lower abdomen. In medical radiography the x-ray beam is adjusted to expose only the area of which an image is required, so that generally shielding is applied to the patient to avoid exposing the gonads, whereas in an airport backscatter scan, the testicles of men and boys will be deliberately subjected to the direct beam in order to check for weapons in the underpants, and some radiation will also reach the ovaries of female subjects. Double - strand breaks in DNA of human sperm has been studied at very high x-ray doses in which they found a linear dose-response relationship at high doses. They did not study the effect at doses as low as would be used in x-ray airport scanners.
Extrapolations of cancer risk from minuscule exposures to radiation across large populations, however, are not supported by analysis by the National Council on Radiation Protection (NCRP). On May 26, 2010 NCRP issued a press release to address such comments about full body scanners that are compliant with ANSI N43.17. In Commentary No.16 issued on May 26, 2010, it reads as follows:
As stated in NCRP Report No. 121 (1995), Principles and Application of Collective Dose in Radiation Protection, the summation of trivial average risks over very large populations or time periods into a single value produces a distorted image of risk, completely out of perspective with risks accepted every day, both voluntarily and involuntarily.
According to NCRP, the use of statistical extrapolations that predict 1 death for every 200 million persons scanned for example (as above) is an unrealistic over-estimation.
Other scientists at Columbia University have made the following statements in support of the safety of body scanners:
"A passenger would need to be scanned using a backscatter scanner, from both the front and the back, about 200,000 times to receive the amount of radiation equal to one typical CT scan," said Dr. Andrew J. Einstein, director of cardiac CT research at Columbia University Medical Center in New York City.
"Another way to look at this is that if you were scanned with a backscatter scanner every day of your life, you would still only receive a tenth of the dose of a typical CT scan," he said.
By comparison, the amount of radiation from a backscatter scanner is equivalent to about 10 minutes of natural background radiation in the United States, Einstein said. "I believe that the general public has nothing to worry about in terms of the radiation from airline scanning," he added.
For moms-to-be, no evidence supports an increased risk of miscarriage or fetal abnormalities from these scanners, Einstein added.
"A pregnant woman will receive much more radiation from cosmic rays she is exposed to while flying than from passing through a scanner in the airport," he said.
Furthermore, other scientists claim the health effects of backscatter are well understood whereas those from millimeter wave scanner
Millimeter wave scanner
A millimeter wave scanner is a whole–body imaging device used for detecting objects concealed underneath a person’s clothing. Typical uses for this technology include detection of items for commercial loss prevention, smuggling and screening at government buildings and airport security...
s are not:
"From a radiation standpoint there has been no evidence that there is really any untoward effect from the use of this device [backscatter scanner], so I would not be concerned about it from a radiation dose standpoint – the issues of personal privacy are a different thing," he said.
The health effects of the more common millimeter wave scannerMillimeter wave scannerA millimeter wave scanner is a whole–body imaging device used for detecting objects concealed underneath a person’s clothing. Typical uses for this technology include detection of items for commercial loss prevention, smuggling and screening at government buildings and airport security...
are largely unknown, and at least one expert believes a safety study is warranted.
"I am very interested in performing a National Council on Radiation Protection and Measurements study on the use of millimeter-wave security screening systems," said Thomas S. Tenforde, council president.
However, no long-term studies have been done on the health effects of millimeter wave scanners.
Experts evaluating backscatter x-ray machine technology have also argued that defects in the machines, damage from normal wear-and-tear, or software errors could focus an intense dose of radiation on just one spot of the body. For example, Dr. Peter Rez, a professor of physics at Arizona State University, has said, "The thing that worries me the most, is not what happens if the machine works as advertised, but what happens if it doesn't," adding that a potential malfunction of the machine could increase the radiation dose.
The designers and manufacturers of backscatter X-ray scanners claim that the scanners are designed to prevent the occurrence of these kinds of errors. The scanners' safety requirements include fail-safe controls and multiple overlapping interlocks. These features, combined with fault analysis, ensure that failure of any subsystem results in non-operation of the x-ray generator to prevent accidental exposures. In the United States, the TSA requires that certification to the ANSI N43.17 safety standard is performed by a third party and not by the manufacturer themselves.
The European Commission
European Commission
The European Commission is the executive body of the European Union. The body is responsible for proposing legislation, implementing decisions, upholding the Union's treaties and the general day-to-day running of the Union....
issued a report stating that backscatter x-ray scanners pose no known health risk, and that "assuming all other conditions equal", that backscatter x-ray scanners, which expose people to ionizing radiation, should not be used when millimeter-wave scanners that "have less effects on the human body" are available.
However, the European Commission report provides no data substantiating its claim that "all other conditions are equal". One area where backscatter X-ray scanners can provide better performance than MM wave scanners, for example, is in the inspection of the shoes, groin and armpit regions of the body.
In a study published in the Archives of Internal Medicine
Archives of Internal Medicine
The Archives of Internal Medicine is a peer-reviewed medical journal published twice a month by the American Medical Association. The Archives of Internal Medicine was established in 1908 and covers all aspects of internal medicine, including cardiovascular disease, geriatrics, infectious disease,...
on March 28, 2011 researchers at the University of California "calculated that fully implementing backscatter scanners would not significantly increase the lifetime risk of cancer for travelers." The researchers calculated that for every 100 million passengers who flew seven one-way flights, there would be one additional cancer.
In May 2011 several scientists, including Agard, Sedat, Shuman, and Stroud from UCSF, complained that TSA's testing of the scanners was inadequate, and that its safety research report was heavily redacted and based on a model of a scanner, not on an actual scanner. Peter Rez, of Arizona State, also worried about mechanical failures that could lead to overdoses.
Justifications for use
Since their health risks were understood, X-rays had previously not been used on humans for non-medical purposes. However, some justify the additional individual risk from exposure to backscatter radiation, by citing benefit to the community as a whole. For instance, if scans are carried out in the interest of public safety then the potential benefit of discovering a weapon on a person could be to the benefit of the community but not to the person being scanned. In other words, a person may be certain they are not carrying a weapon and may gain little by being scanned but the act of undergoing a scan may benefit other passengers.Safety regulations and standards
In the US, manufacturers of security related equipment can apply for protection under the SAFETY act, which limits their financial liability in product liability cases to the amount of their insurance coverage. The Rapiscan Secure 1000 was listed in 2006.In the US, an X-ray system can be considered to comply with requirements for general purpose security screening of humans if the device complies with American National Standards Institute (ANSI) Standard #N43.17.
In the most general sense, N43.17 states that a device can be used for general purpose security screening of humans if the dose to the subject is less than 25 μrems
Röntgen equivalent man
Named after Wilhelm Röntgen , the roentgen equivalent in man or rem is a unit of radiation dose equivalent...
(0.25 μSv
Sievert
The sievert is the International System of Units SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in gray...
) per examination and complies with other requirements of the standard. Twenty-five micro Rem is equal to the amount of background radiation every human is exposed to (from the air and soil) at sea level every 1.5 hours and is also equal to the radiation exposure from cosmic rays when travelling in an airplane at altitude for 2 minutes.
Many types of X-ray systems can be designed to comply with ANSI N43.17 including transmission X-ray, backscatter X-ray and gamma ray systems. Not all backscatter X-ray devices necessarily comply with ANSI N43.17; only the manufacturer or end user can confirm compliance of a particular product to the standard.
ANSI standards use a standard of measurement algorithm called "effective dose" that considers the different exposure of all parts of the body and then weights them differently. The interior of the human body is given more weight in this survey and the exterior including the skin organ are given less weight. The Rapiscan
Rapiscan Systems
Rapiscan Systems is a global privately held company that specializes in walk-through metal detectors, and x-ray machines for airport luggage and cargo screening...
backscatter machine produces an X-ray more absorbed by the skin than most other X-ray devices but is still regulated under the ANSI. The standard for "effective dose" damage done to the skin by X-rays is similar to the damage done by sunlight. http://www.youtube.com/watch?v=eS0UxXDNs4w
The European Union is currently considering whether it is acceptable for this technology to be deployed in European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...
airports. A report is pending from the Transport Committee of the European Parliament
European Parliament
The European Parliament is the directly elected parliamentary institution of the European Union . Together with the Council of the European Union and the Commission, it exercises the legislative function of the EU and it has been described as one of the most powerful legislatures in the world...
.
Technical countermeasures
Some people wish to prevent either the loss of privacy or the possibility of health problems or genetic damage that might be associated with being subjected to a backscatter X-ray scan. One company sells X-ray absorbing underwear which is said to have X-ray absorption equivalent to 0.5 mm of lead. Another product, Flying Pasties, "are designed to obscure the most private parts of the human body when entering full body airport scanners", but their description does not seem to claim any protection from the X-ray beam penetrating the body of the person being scanned.See also
- Visible Intermodal Prevention and Response teamVisible Intermodal Prevention and Response teamA Visible Intermodal Prevention and Response team, sometimes Visible Intermodal Protection and Response is a Transportation Security Administration program. Various government sources have differing descriptions of VIPR's exact mission...
- Explosives trace-detection portal machine (puffer machine)
- Future Attribute Screening TechnologyFuture Attribute Screening TechnologyFuture Attribute Screening Technology is a program created by the Department of Homeland Security. It was originally titled Project Hostile Intent...
- Millimeter wave scannerMillimeter wave scannerA millimeter wave scanner is a whole–body imaging device used for detecting objects concealed underneath a person’s clothing. Typical uses for this technology include detection of items for commercial loss prevention, smuggling and screening at government buildings and airport security...
- Full body scanner
External links
- Z-Backscatter Van — video of a backscatter x-ray, mounted on surveillance trucks.
- Full-body scans of fliers set off debate over privacy, health
- University of Florida Research — High Resolution Scatter X-ray Imaging
- Rapiscan Systems
- Backscatter X-ray technology and risks