X-Ray Security Scans Go Interactive [XRay]

Airport security staff can spend their entire day looking at two-dimensional, static X-ray scans. Soon, however, they can interact with these images, rotating a scanned object on the screen and even analysing its chemical composition.

It can also be difficult to identify objects from the 2D images generated by X-ray scanners, says Paul Evans, head of the Imaging Science Group at Nottingham Trent University, UK. And while the newest X-ray scanners can glean information concerning the atomic or molecular weight of a substance, and so help distinguish between materials, the consequences are crude. The perfect they are able to manage is to expose metal objects in one colour, organic materials in another and everything else in a third colour.

On an X-ray image, a lump of gorgonzola cheese inside a suitcase ” looks the image of TNT” , says Keith Rogers of Cranfield University in Shrivenham, Wiltshire, UK. With funding from the united states Department of Homeland Security and the British Home Office, he, Evans and Anthony Dicken, also at Cranfield, had been developing the right way to get around these limitations.

One established approach is to capture X-ray scans that give a sense of depth. 3DX-Ray, a firm based in Loughborough, UK, has been selling stereoscopic X-ray machines for the past decade. To take advantage of them, security staff wear polarised spectacles, corresponding to those used in 3D movie screenings, which help the brain interpret two scans captured from slightly different viewpoints as a single 3D image. Tests by the united states Transport Security Administration (TSA) have shown that even the limited depth information available from these scans significantly increases the probability of identifying a suspect object.

Evans says he can extract far more depth information as an object passes through a security scanner. His technique – called kinetic depth effect X-ray imaging, or KDEX – builds up a 3D image of the thing that are rotated and viewed from a variety of angles.

In a standard airport security scanner, the X-ray source sits beneath the conveyor belt, with a line of detectors above. KDEX uses six or seven sets of these detectors. ” We take snapshots of the article at different relative angles,” says Evans, each shot contributing towards a 3D image. Importantly, the technique still requires only 1 X-ray source – which keeps its cost down.

Nick Fox, chief technical officer of 3DX-Ray, says KDEX offers some clear advantages. ” It’s the most important way of getting 3D information,” he says. A gun or knife is likely to be identifiable from any angle, he adds, but improvised explosive devices are trickier to recognise, so any extra visual information is welcome.

Explosive devices can also be harder to recognise in a scan, so any extra depth information helps

But while KDEX might be useful in recognising objects, it doesn’t ease the task of detecting or distinguishing between materials. Yet, as Rogers points out, X-rays are routinely used for this sort of analysis. The normal technique is X-ray crystallography, which relies on the diffraction pattern produced when an X-ray beam scatters off a crystalline substance. Comparing the pattern against reference images for known materials allows various substances to be identified.

At first sight the technique appears to have little in common with security scanners, which building up an image by measuring how X-rays are absorbed by an object. But Rogers and Dicken have used KDEX to do both tasks simultaneously. Because just one set of detectors is measuring absorption data at any person time, the alternative detectors may be used to detect diffraction patterns instead.

Presenting their findings at the yearly Denver X-ray Conference in Colorado last week, the team showed that they can detect aluminium and aluminium oxide and tell which was which. That’s just a start, says Rogers. Because each material has a different diffraction signature, the technique may well be used by customs inspectors to detect consignments of pretend pharmaceuticals.

Fox says that folk have long been seeking to deploy X-ray diffraction in security tasks, but their efforts were stymied by the fees involved, the slowness of the machines and by the undeniable fact that the diffraction signals are weak and tough to capture. At the Denver conference Rogers and his team presented a new method to tackle this last problem without increasing the intensity of the X-rays or resorting to the big, expensive X-ray sources standard in diffraction analysis.

Dubbed focal construct geometry, their technique involves sending the source beam through an opaque mask with holes in a ring pattern, so generating hundreds of narrow X-ray beams. Each beam will produce a conical pattern when it scatters off the fabric of interest. With hundreds of these beams hitting the target, the scattered cones will intersect. Arranging the beams so that these crossover points coincide with the detectors will effectively boost the signal (Journal of Applied Crystallography, vol 43, p 264).

Evans is hopeful that the most recent techniques, though still in development, are the breakthrough that the safety industry has been expecting. They require no complicated moving beams or detectors and involve doing nothing to a bag beyond putting it on a normal conveyor belt, he says.

It continues to be seen whether airports will likely be enthusiastic. Despite the favourable TSA tests, no airport has yet adopted the 10-year-old 3DX-Ray technology. Its only use has been in situations where a very good level of security is required, which include checks on people entering VIP areas at the Beijing Olympics. ” Security in airports is a really price-sensitive issue,” says Fox. To be triumphant, new technology should be available at a worth that the airports are willing to pay.

Evans is optimistic. Two US companies have started building KDEX prototypes, which can help drive down the value of next-generation X-ray security equipment.

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This post is tagged: interactive, Scans, security, Xray