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Feature Articles

Airport X-ray Machines Go Mainstream with Move to PCI Architectures

by Winn Hardin, Contributing Editor - AIA

Following the terrorist attack on the World Trade Center on September 11th, all forms of airport security have gained public attention, from the need for more US Air Marshals to mandatory baggage inspection for explosive devices. The US Congress proposes that between 2003 and 2006, US airports match European regulations requiring 100 percent baggage inspection. Today, international terminals already face a looming deadline to meet the European regulation.

Luckily for US air passengers and airport authorities alike, the US Congress has promised millions of dollars to help achieve these goals. In fact, a Federal Aviation Administration (FAA) project, called Argus, was scheduled to conclude testing of a new category of explosive detection systems (EDS) for luggage by the end of 2001. The program plans to deploy low cost (<$300k) x-ray scanning EDS systems in small airports nationwide starting in the summer of 2002.

The widely deployable Argus systems represent a windfall contract to x-ray scanning companies in the airport security industry. Prior to September 11th, analysts estimated that cumulative EDS equipment revenues would top $1 billion between 2001 and 2006. Today, that number could be spent in the US by 2004. To meet the contract, however, x-ray inspection systems composed of transmission, backscatter, computed tomography (CT) and diffraction technologies need to find ways to reduce the cost per unit while maintaining high-reliability, high-throughput scanning systems.

Baggage inspection looks to the shelf
Joe Sgro, CEO of frame grabber and image processing board manufacturer Alacron Inc. (Nashua, NH), has witnessed the recent upsurge in airport security and the opportunities it affords traditional machine vision companies. His company has worked with new inspection technologies, such as millimeter wave imaging conducted at the US Pacific Northwest National Laboratories (Richland, WA), in addition to commercial x-ray baggage inspection systems in both the US and UK.

"All of our customers used to be VME and are now moving to PCI," Sgro observed, "mostly for cost, plus an open NT source environment using off the shelf equipment." According to Sgro, the US will deploy approximately 2000 x-ray baggage inspection units in 2002 in response to September 11th and federal programs such as Argus. Between now and then, the baggage inspection systems are going through a furious development schedule to meet new federal specifications of high reliability (actual false alarm rates and minimum detection levels are classified) at varying speeds (depending on airport size) and a lower cost per unit.

Out of the four main technologies, three are actually considered viable for airport baggage inspection: transmission, backscatter and CT. The fourth, diffraction x-ray imaging, keys on the crystalline nature of the explosive under test. It is highly reliable, but very slow and expensive, explained Francois Mesqui, Ph.D., Chief Technology Office at InVision Technologies Inc. (Newark, CA), one of two major manufacturers of CT systems for security applications in the US. Out of the remaining three, Alacron's Sgro groups backscatter and transmission into one category and computed tomography into a second category, although the x-ray security manufacturers use different combinations and variations on these methods to improve their system's performance in a variety of ways.

"The InVision and L3 [Communications, New York, NY] CT technology is the most accurate," Sgro said, " but the most difficult to do in terms of throughput, real-time and everything else. You can lower the cost of the CT systems, but there's an inherent amount of intensive calculations [for these systems.] The people with [transmission and backscatter] use artificial coloration and image enhancement for high-speed throughput and to aid in training. So that's the upper and lower markets. If someone can come up with a transmission scheme that makes FAA certification it will obviously have an advantage in the market. The CT people have the advantage in terms of technology, but disadvantage in terms of cost. Historically in the US, whenever there's an impossible problem, someone solves it. Either CT will get cheaper or transmission will meet [FAA] requirements."

High-throughput systems and false alarm rates
PerkinElmer Detection Instruments (Woburn, MA) and American Science & Engineering (Billerica, MA) are two of the most well known transmission and backscatter x-ray inspection system manufacturers. PerkinElmer's x-ray instruments were actually an acquisition of a company called Vivid Technologies that was spun off of a medical x-ray equipment manufacturer, similar to InVision Technologies.

PerkinElmer uses a dual energy system to determine the Z-effect or average atomic weight of materials along the optical axis between an x-ray source and linear array of silicon detectors. By measuring the changes in Compton scattering and photoelectric effect of x-ray/atom interactions at 75 and 150 keV along with spatial information, PerkinElmer's VIS-108 mainframe detects and displays explosives in baggage at throughputs of 1800 bags per hour. PerkinElmer Detection Instrument's vice president of product and business development, Michael Ellenbogen, said that his company redesigned the VIS-108 to move away from a VME backplane powered by image processing boards to a single board computer approach with standard PCI bus that depend on a proprietary boards with pairs of Analog Devices (Norwood, MA) Sharc digital signal processors.

By adding the backscatter measurements to the high-energy transmission x-rays, AS&E representatives claim to better differentiate lower atomic weight organic materials systems, such as drugs and explosives, in their cargo container inspection while transmission x-rays reveal spatial details. CT systems on the other hand, key on density measurements of specific objects. "Remember, we're not looking for guns, so we can't use shapes," explained InVision's Mesqui. "You can mold explosives into almost any shape. What we recognize is differences in density from the transmission x-ray to start the CT scan for finer detail."

Slower, but more accurate
When a third dimension is added to the x-ray system, the calculation requirements increase by at least an order of magnitude, slowing system's throughput. Slow throughput means an airport's baggage handling system needs more inspection units to handle the same number of passengers compared to a x-ray transmission-based system and at price per units of up to $1 million for CT systems compared to tens of thousands for transmission inspection systems, the need for federally funded research to improve these systems becomes blindingly apparent.

"The processing requirements for these two systems are around a gigaflop per second for CT and hundreds of megaflops for transmission systems, but that's going to converge as people try to meet the standards," said Alacron's Sgro. Some convergence is already in evidence. PerkinElmer has a three fixed-head x-ray transmission system that hopes to provide 3D scans similar to CT systems with two to three-times the CT throughput. InVision's approach uses transmission first to detect specific regions of interest and then performs CT on those regions to speed luggage on its way to the plane or human inspectors. So far, InVision makes the FAA certification on false alarms and detection levels, but is still priced over the federally dictated $300,000 pricetag for the Argus project; PerkinElmer has yet to achieve the FAA false alarm rates although Ellenbogen said he is confident they will in time for the Argus program deadlines.

Most of the pieces seem to be in place to meet the nation's needs for faster, cheaper x-ray baggage inspection equipment, according to Alacron's Sgro. Now it is just a matter of bringing the pieces together. Board manufactures such as Alacron, who cannot disclose its US manufacturing partner in the x-ray baggage inspection industry, and Kaiser (San Jose, CA) in the case of PerkinElmer are helping OEMs meet the extremely short technology insertion schedules devised after September 11th. They are winning the support of the OEMs in some cases by opening their technology roadmaps to the OEMs and ensuring long-term support for processing boards, such as in the case of Kaiser and PerkinElmer. Another piece, memory, is also meeting system needs thanks to dual- and quad data rate (DDR, QDR) on-chip front buses; and because these systems do not inspect people, there is plenty of power budget for the detectors at high throughputs. Medical CT manufacturers have already dipped below the FAA mandated $300,000 price tag -at much slower throughputs than those proposed for luggage inspection, however. In the end, the key element may lie in the algorithm that can combine enough different measurements fast enough to tell whether grandma is carrying a bar of soap, or 8 oz. of Semtex plastique.





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