X-ray Imaging for Security Screening Applications

Pioneering research at NTU on 3D X-ray imaging signalled a breakthrough in multiple-view imaging which has had significant and worldwide impact on the security industry and public safety. It is a prime tool in tackling terrorist activity, particularly explosives concealed in luggage. NTU's divergent beam technique is central to many advanced technology systems used by international security manufacturers.

The prime impact of the University's divergent beam X-ray work over the last 25 years has been to counter the threat of terrorist activity, particularly in the form of concealed explosive devices in baggage being placed on board aircraft.

Commercialisation and product development

A portfolio of advanced real-time X-ray screening systems has been developed with applications in both the security and industrial inspection markets.

Due to the success of NTU's programme of research, the DHS issued a broad agency announcement to US industry to build prototype scanners based on NTU's technique. Professor Paul Evans was part of the broad agency announcement process and was contacted directly by nine different US security manufacturers to advise on KDEX design and implementation.

NTU led the formation of the spinout company Halo X-ray Technologies Ltd in partnership with Cranfield University, in 2012 to exploit its work in X-ray diffraction imaging. One patent was granted to the company in 2013 and there are a further four patents pending.

Worldwide industrial impact

NTU's divergent beam technique has become the de facto standard for obtaining multiple views from a stationary X-ray source. It is routinely incorporated into advanced technology systems (those featuring enhanced detection capabilities) by international security manufacturers to produce compact and cost-effective machines.

Worldwide influence

The University's researchers have provided feedback and carried out research for the US Department of Homeland Security and the UK Home Office Centre for Applied Science and Technology (CAST) as part of their Innovative Research Calls IRC2007 and IRC2010 research contracts. This has helped to inform and support scientific thinking in the UK and US governments concerning the use of diffracted X-rays for the identification of explosive substances and contraband drugs.

The following personal invitations are further evidence of impact.

• The Government Chief Scientific Adviser (GCSA), Government Office for Science personally invited Professor Evans onto a national panel of experts in 2010. The panel incorporates a select number of leading academics.
• An invitation to speak at the Gordon Research Conference on Detecting illicit substances: Explosives and drugs, Switzerland, May 26-31, 2013.

Award-winning research

The impact of Professor Paul Evans' research was recognised as part of NTU’s Queen’s Anniversary Prize 2015 Award. This is the highest national honour for a UK university.

Professor Paul Evans has conducted research on 3D security X-ray imaging for over 25 years. In 1993 he was working on a unique divergent beam X-ray technique as part of a collaborative team led by Professor Max Robinson at NTU and at the Home Office by Professor Dick Lacey, Chief Scientist Chemical, Biological, Radiological, Nuclear and Explosive (CBRNE).

A major problem for aviation security was the total lack of depth information in simple X-ray scans. The screener searched routinely for threats such as weapons and improvised explosive devices amongst everyday objects. Serious misinterpretations of objects caused increased false alarms and reduced throughput.

Drawing on Robinson's earlier work, Evans conceived a breakthrough that enabled high-quality stereoscopic images to be produced using folded detectors. This insight enabled him to design the world's first X-ray scanner incorporating a stereoscopic folded array. It comprised dual energy detectors enabling organic and metallic objects to be encoded with different colours.

A single X-ray source enabled a compact and cost-effective solution. Critically, the technology offered the same throughput as standard single-view machines. In 1996, a company was formed to exploit original research by the University led by Robinson on stereoscopic X-ray imaging.

To remove the requirement for stereo glasses, Evans devised a new multiple-view technique to produce dynamic depth. In 2000, assisted by his PhD student Hock Woon Hon, Evans demonstrated a small-scale version to the Home Office. The technique exploited kinetic depth effect (KDE), which enables the observer to work out the shapes of objects with remarkable accuracy from their shadows during a rotation. This was the first demonstration of KDE using divergent beams. A full-scale scanner was built in collaboration with Lacey at the Home Office.

The US Department of Homeland Security funded a six-year rolling research programme to evaluate the performance of kinetic depth X-ray imaging for luggage screening. This work culminated in a broad agency announcement to US industry to build a prototype KDE scanner.

To reduce the cost of the detector arrays required for KDEX, Evans conceived a new type of castellated dual energy detector. Assisted by PhD student Jer Wang Chan, in 2004 he demonstrated that the total number of detector elements composing an array could be reduced by 50% without affecting the quality of the imagery. The work was funded by the EPSRC and carried out in collaboration with the Home Office Scientific Development Branch. It formed the basis of a range of products now commercially available through 3D X-RAY Ltd.

Professor Evans leads a collaboration with Professor Rogers at Cranfield to combine the two primary but discrete fields that evolved and developed disparately from the discovery of X-rays, i.e. radiology and crystallography, with scatter-enhanced KDEX. To develop true high-speed materials identification capability, a new patented tomographic approach employing hollow X-ray beams increases by orders of magnitude the intensity of the material signatures. The work is funded under CONTEST, the UK's counter terrorism strategy.

• A letter from the CTO of 3DX-RAY, which is the main trading subsidiary of Image Scan Holdings plc. "There are examples of divergent beam techniques in the product ranges of all the major manufacturers of advanced technology (AT) X-ray screening systems. This global impact is not surprising as the NTU technique enables the real-time capture of 3D imagery, which was only previously possible with large and prohibitively expensive multiple sources and extended radiological shielding."
• Evans demonstrated Surround View at its product launch during an interview broadcast by the BBC TV World Service from the Transport Security Expo Olympia in London, November 2012.

• Dicken, A., Rogers, K., Evans, P., Chan, J.W., Rogers, J. and Godber, S., 2011. Combined X-ray diffraction and kinetic depth effect imaging. Optics Express, 19. 6,414
• Evans, P., Rogers, K., Chan, J., Rogers, J. and Dicken, A., 2010. High intensity X-ray diffraction in transmission mode employing an analog of Poisson's spot. Applied Physics Letters, 97
• Rogers, K., Evans, P., Rogers, J., Chan, J W. and Dicken, A., 2010. Focal construct geometry - a novel approach to the acquisition of diffraction data. Journal of Applied Crystallography, 43. 264
• Chan, J.W., Evans, J.P.O., Yen, S.Y. and Monteith, A. (Home Office), 2004. Wire transfer function analysis for castellated dual-energy X-ray detectors. Applied Optics, 43. 6413
• Evans, J.P.O. and Hon, H.W., 2002. Dynamic stereoscopic X-ray imaging. NDT & E International, 35. 337
• Evans, J.P.O., Robinson, M. and Godber, S.X., 1996. A new stereoscopic X-ray imaging technique using a single X-ray source: Theoretical analysis. NDT & E International, 29. 27