About this Article
Written by: Farzana Ansari
Written on: July 11th, 2005
Tags: electrical engineering, security & defense
Thumbnail by: Adam Ciesielski/SXC
About the Author
In the summer of 2005, Farzana Ansari was a sophomore majoring in Biomedical Engineering at the University of Southern California. Her love of traveling compelled her to take a deeper look into the airport security systems she has encountered.
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Volume IX Issue II > Security Versus Privacy: The Engineering of X-Ray Vision
In the post-September 11 era, engineers have developed new technologies to meet growing safety and security concerns at the world's airports. The drawbacks of existing security measures - especially physical pat downs - have provided a foundation for "backscatter" X-ray technology. Information offered by the Transportation Security Administration and American Science and Engineering, Inc., demonstrate how backscatter X-ray devices combine basic physical concepts with established scanning technology to create a virtual strip search. The revealing images that are produced have raised concerns of privacy violations presented by this modern-day form of X-ray vision. The powerful potential of backscatter X-ray technology as a security system will ultimately depend on passengers' trust of TSA officials and airport scanners.


Adam Ciesielski/SXC
Figure​ 1: X-ray images show features below the skin.
X-ray vision: a phenomenon associated with the fantastic, the futuristic and, above all, the fictional. For many, the term alludes to Superman's rare ability to see through walls in search of enemies or through clothing to find hidden weapons (Fig. 1). As mythical as X-ray vision seems, this ability has already been incorporated into modern reality-and the superhero responsible is the engineer.
Technology has played a significant role in the reorganization and advancement of airport security systems since the terrorist attacks of September 11 and the threats that ensued. The days of sporadic pat-downs and occasional bag scans have long since passed. Today, passengers arrive at airports over three hours before their flights in anticipation of long lines for metal detectors and luggage checks. The environment of fear developed after the World Trade Center and Pentagon attacks suspended concerns about the issue of privacy violation versus necessary precautions. However, recent advancements in airport security have reinstated these concerns with the introduction of "backscatter" X-ray technology.
Backscatter X-ray machines perform virtual strip-searches: air travelers are scanned from head to toe to produce a 360-degree image that literally sees through their clothes. While metal detectors only reveal metallic items, the high-resolution backscatter X-ray images disclose plastics, ceramics, and chemicals as well. This exposure, however, also comes with a detailed view of the traveler's naked body, providing airport screeners with what some consider a too-realistic form of X-ray vision. The engineering of this controversial superpower combines fundamental physics concepts with innovative technology, fueling a renewed debate of privacy versus precaution at the airport.

Motivations for Better Technology

X-ray technology was integrated into medical CAT (Computerized Axial Tomography) Scans by Robert S. Ledley in 1975 and incorporated into airport security systems in the 1990s [1]. Today, X-ray scans are primarily performed on checked and carry-on luggage. The machines detect inorganic materials (plastics, ceramics, and metals) found inside a majority of containers, without exposing nearby operators and passengers to harmful amounts of radiation [2]. Since the 1990s, the Transportation Security Administration (TSA) has employed an X-ray device called the Explosive Detection System (EDS) in all airports, increasing distribution significantly since September 11 [3].
The accuracy of the EDS was debated even before the terrorist attacks on the World Trade Center and Pentagon [4]. The numerous security failures of September 11 and subsequent threats have spurred TSA to take action on pinpointing where shortcomings originate in the system. Studies have revealed that technological inadequacies of X-ray machines in scanning luggage have not been the cause of the inconsistencies. Rather, human error in screening passengers has proved to be a significant concern, as seen in TSA's October 2006 tests at Newark Liberty International Airport. Newhouse News Service reported that screeners "missed fake explosive devices taped beneath an agent's clothing and concealed under a leg bandage another tester wore." Furthermore, screeners "failed to use handheld metal-detector wands when required, [and] missed an explosive device during a pat down" [5].
While a lack of training may be causing these failures, another source is the issue of privacy violation provoked by physical pat downs. Frisking, especially in the upper torso area on women, introduces difficult questions of sexual harassment. The situation is uncomfortable for both passengers and screeners, and has triggered complaints [6]. In an effort to eliminate this dilemma, TSA wants to limit human involvement in passenger screening, providing the motivation for backscatter X-ray machines.