The decision by Umar Farouk Abdulmutallab and his terrorist handlers to conceal high explosives in Abdulmutallab's underpants on a Detroit-bound flight on Christmas has led to renewed interest into whole body imaging technology, or full body scans, to detect contraband passengers may smuggle onboard an airplane.

Already, the British, French, Dutch, and Nigerian governments say they will embrace the technology, which allows operators to peer underneath a passenger's clothes and identify hidden threats on their body. The European Union, which overwhelmingly said no to the technology in 2008, is reconsidering its position post-Detroit, reports The Christian Science Monitor. And yesterday, Homeland Security Secretary Janet Napolitano said her department will accelerate the deployment of whole body imaging technology at U.S. airports. There are already about 40 machines deployed at certain airports nationwide, but Napolitano said the Transportation Security Administration (TSA) will fast track at least another 300 units into the field this year.

This increased push for whole body imaging, however, has led to fears that the technology unnecessarily violates passengers' privacy rights and even their health. So what's true and false about whole body imaging technology?Security Management  has scoured publicly available information to answer some of the most pressing questions.

How does whole body imaging technology work?

That depends, because there are two different ways to generate a full body image: millimeter wave technology and backscatter technology.

How do these technologies differ?

Millimeter wave technology beams the passenger with millimeter wave radio frequency (RF) energy from two antennas that spin around the passenger at very fast speeds from head to toe. The energy reflected off the body and other objects generates a three-dimensional image of the passenger's body and anything else carried on his person.

Backscatter technology, however, uses very weak X-rays to generate a two-sided image of a passenger and anything else on that person's body.

Do these technologies identify the same types of threats?

Yes. Manufacturers of each technology say their respective technologies can detect the same types of threats.  L-3 Communications' machines, which use millimeter wave technology,  boast that they can "reveal and pinpoint hidden weapons, explosives, drugs and other contraband."

RapiScan, which uses backscatter technology, states that its machines screen passengers "for a wide range of potential threats including liquids, contraband, ceramics, explosives, narcotics, concealed currency and weapons." American Science and Engineering (AS&E), another manufacturer of backscatter technology, says its system "displays both organic and inorganic materials, revealing objects such as guns and knives, liquid and plastic explosives, composite weapons, and other hidden threats and contraband."

On its Web page devoted to whole body imaging, the TSA makes no distinction between the types of threats each technology can detect.

Are these technologies safe?

The consensus seems to be yes. The American College of Radiology (ACR)recently released a statement vouching for the safety of each type of technology. "The ACR is not aware of any evidence that either of the scanning technologies that the TSA is considering would present significant biological effects for passengers screened."

But there is a difference between the two types of technology. Backscatter technology exposes passengers to ionizing radiation, much like medical X-rays, while millimeter wave technology does not, reports Reuters. Instead, millimeter wave technology "uses radio signals akin to cell phone RF energy," reports DotMed.com. "Since the millimeter waves are low-level radio waves, the radiation is non-ionizing and so it is considered completely safe."

Despite this, the X-ray dose used by backscatter machines is extremely low. Dr. James Thrall, chair of the ACR and chair of radiology at Massachusetts General Hospital in Boston, told ABCNews.com that a passenger "would have to take hundreds and hundreds of trips requiring screening to even reach what would be considered a negligible dose."

On their Websites, both RapiScan and AS&E address radiation fears explaining that a passenger will receive considerably higher radiation doses once they've been flying for an hour or two than they will undergoing screening with backscatter technology.

Nevertheless, L-3 Communications, which manufactures millimeter wave scanning technology, states that its machines screen people "without exposure to harmful electromagnetic radiation."

Are privacy concerns legitimate?

Yes and no. Both whole body imaging technologies display anatomically correct images of the person screened, which is why some civil libertarians liken this screening to "virtual strip searches." The ACLU yesterday released a new backgrounder on the technology yesterday, stating it "reveals not only our private body parts, but also intimate medical details like colostomy bags. Many people who wear adult diapers feel they will be humiliated."

The TSA as well as the manufactureres of the technology say they have taken many steps to protect the identity of the passenger being screened. AS&E's backscatter technology can be privacy-enhanced, according to the company. When the image is generated, it looks like a chalk outline of the passenger which also "outlines any potential threats on the person -- similar to when a child traces an outline of his/her hand" without "revealing images of the body." The machines that use millimeter wave technology produces an image that looks like a photo negative, but the faces of passengers are blurred, according to the TSA.

The agency also says it has  implemented privacy protections into the screening process when using this technology.

When a passenger is screened, the TSA officer that assists the passenger never sees the image. The TSA officer that views the image is in a remote, secured viewing room, ensuring she never sees the passenger's face. The two officers communicate via headset. Once the remotely located TSA officer looks over the image and verifies that the passenger has no contraband, she signals to the TSA officer assisting the passenger to let the passenger continue on through security.

As another safeguard, the ability of the machines to store, print, transmit, or save the image is disabled before the machines are delivered to airports. TSA officers are further barred from bringing cameras, cell phones, or photo-enabled devices into the viewing room as one more privacy protection. 

(Assistant Editor Joseph Straw also discussed whole body imaging in the Sept. 2008 feature "New Views on Airport Screening.")

♦ Photos of whole body images by TSA