This PDF file contains the front matter associated with SPIE Proceedings Volume 11738, including the Title Page, Copyright information, and Table of Contents.

Gratings-based phase contrast x-ray imaging offers enhanced material information in an x-ray imaging measurement, a key consideration for improving performance in explosives detection. Application of phase contrast imaging to explosives detection requires addressing several key technical issues: identifying a patterning element (grating) that offers an appropriate tradeoff between sensitivity and robust operation at high energies, developing techniques that allow for quantitative interpretation of new signatures under a broad range of attenuation conditions, and designing a system that allows for rapid measurement while providing sufficient signal-to-noise. We present results illustrating the value of phase contrast x-ray signatures for explosives detection, and demonstrate the ability to obtain quantitative metrics in the presence of intervening materials. Finally, we demonstrate preliminary results from a gratings-based phase contrast system in a scanning configuration.

Gratings-based phase contrast X-ray imaging provides additional materials signatures in textured media based on the deflection of the X-ray beam. Using this technique with a hard (~160 kVp) X-ray spectrum has shown potential for improved materials discrimination in applications such as explosives detection. Typical phase contrast measurements rely on relatively broad bremsstrahlung spectra, resulting in measurement responses averaged across wide energy ranges. Here, we present results for gratings-based phase contrast measurements using a spectroscopic imaging detector. This allows for direct observation of phase-contrast material cross sections as a function of energy, without the need for a mono-energetic X-ray source. Further, the measurements provide a direct understanding of spectral variations and a technical basis for application of hard X-ray gratings-based phase contrast measurements in the presence of attenuating materials.

Medicine counterfeiting is a health and economic problem that the pharmaceutical field has to deal with. X-ray diffraction, known to be very specific in characterizing the structure of molecules, can be an interesting technique for detecting counterfeit drugs without having to take them out of their packaging. In this context, we have developed a relatively compact system which combines the use of an integrated X-ray source and a compact high-performance CdZnTe imager. This system has been tested on several drugs and has shown its ability to easily detect counterfeit pharmaceuticals in their packaging in less than a few minutes.

Detecting illegal drugs in mailed packages without opening the package is a challenge. X-ray diffraction tomography offers the potential capability of uniquely identifying illegal drugs within a package based on their atomic structure. To understand the separability of different drug classes, we generated a library of X-ray diffraction drug signatures and explored them using dimensionality reduction techniques. In addition, we used a compact, multi-modality fan beam Xray imaging system (combining transmission and X-ray diffraction) to distinguish oxycodone from non-prescription medicine when concealed within different types of containment.

Aviation security, mail inspection, medical diagnostics and many other industries all face the same challenge: to accurately identify the presence of a target material concealed within a cluttered surrounding environment. X-ray systems that combine transmission and diffraction measurements promise excellent detection performance with low false alarm rates; however, conventional approaches to combining these measurements typically under-utilize the available information and result in higher overall system resource costs. Here, we consider a fully integrated approach to hybrid X-ray transmission and diffraction systems and discuss simulation- and experimental-based investigations of the design and performance (both imaging and detection) of such systems. Based on this analysis, we describe a hybrid system capable of scanning boxes and/or luggage and report its ability to distinguish materials of interest to aviation security and pharmaceutical inspection.

Here we introduce a new reconstruction technique for two-dimensional Bragg Scattering Tomography (BST), based on the Radon transform models of (Webber, James W., and Eric L. Miller. "Bragg scattering tomography." arXiv preprint arXiv:2004.10961, 2020). Our method uses a combination of ideas from multibang control and microlocal analysis to construct an objective function which can regularize the BST artefacts, e.g., the boundary artefacts due to sharp cutoff in sinogram space, as observed in (Webber, James W., and Eric Todd Quinto. "Microlocal analysis of generalized Radon transforms from scattering tomography." arXiv preprint arXiv:2007.00208, 2020), and errors due to attenuation and Compton noise. We then go on to test our algorithm in a variety of Monte Carlo (MC) simulated examples of practical interest in airport baggage screening and threat detection.

Dual-energy computed tomography (DECT) is widely used to identify explosives or otherwise characterize substances relevant to transportation security screening. However, DECT data taken with energy-integrating x-ray detectors are susceptible to the effects of beam hardening, which can introduce cupping and streaking artifacts into reconstructed images, thereby complicating image analysis. While photon-counting detectors can circumvent this issue by retaining the full spectrum of attenuation information for a probed material, the effects associated with charge sharing among pixels and pulse pile-up can introduce other errors if left uncorrected. Techniques were devised for using basis material decomposition (BMD) as a calibration to correct for the non-linear response of photon-counting detectors. The attenuation spectra from copper, aluminum, and polyethylene phantoms were used as basis functions that could reproduce the attenuations of other measured materials. Material properties relevant to detection, such as linear attenuation coefficient (LAC), electron density (ρe), and effective atomic number (Ze), can then be accurately calculated from energy-resolved CT data. In addition, the calibrated data could produce reconstructed images that were relatively free of the beam hardening artifacts associated with traditional DECT.

Speckle-based X-ray phase contrast imaging (XPCI) is a relatively simple implementation of phase contrast imaging. At low energies, the technique has been demonstrated with masks made from steel wool and sandpaper. However, these materials are too transparent for higher energy applications. The simple geometry and easy identification of, or fabrication of, materials for relevant speckle masks make speckle-based XPCI a compelling technique for widespread use. We have analyzed the trade space for higher energy speckle-based XPCI systems based on portable X-ray tube sources. We have demonstrated several fabrication techniques compatible with a range of materials. Together these enable variation in feature size, material density, and randomness in the mask. This ability to tune the mask parameters allows optimization of the mask for the application space and system design.

We describe a novel fast, automatic and low-cost approach to screening bags for mass casualty threats at sports events, visitor attractions, transport hubs and other publicly accessible locations. This uses simple dual energy X-ray imaging combined with additional microwave radar and optical sensors designed to distinguish benign bags from those containing large explosives or weapon threats. An algorithm based on machine-learning techniques provides automatic detection without the need for an operator to view any image. A prototype has been developed and shown to be able to screen in excess of 1000 bags/hour with high detection and low false alarm rates. Algorithm testing using data from real-life bags taken from a major London visitor attraction and threat bags containing representative firearm and simulated IED threats gave a detection rate of 90% with a corresponding false alarm rate of 2.5% and 95% at 7% false alarms.

This paper describes a method to acquire actual image data of any material, which could be an explosive or parametric simulant, extract the X-ray features of the object, modify the images in a variety of controlled ways, and record new images. All of the augmented images can then be run through the emulator of the baggage screening system to explore the detection algorithm’s performance. This is similar to the method that was demonstrated over a decade ago, where the Transportation Security Laboratory developed a series of explosive simulants which spanned the X-ray feature space of mass density and effective atomic number, thus demonstrating the capability to effectively map out the performance of explosives detection systems in that feature space. In this paper, the concept has been expanded to include synthetic data, which is far more efficient than creating fully synthetic data and greatly diminishes the need to collect data using real explosives.

The conflicting goals of enhancing passenger security and improving the passenger travel experience have created challenging screening requirements and increased the difficulty of resolving alarms, reliably and quickly. The current implementation of standalone airport screening devices needs to progress and support the interoperability of those devices. This ability will allow for increased passenger safety, reduced cost, and scalability to support the growing number of air travelers. The vision of the interoperable airport requires aviation screening systems to communicate and work seamlessly with each other. Each stage in the screening process must be able to communicate, from one source to another, in a secure fashion. The first step in achieving this is to have a standard data format and communication interface between the screening devices. The standard format will facilitate the integration of screening devices, allowing for a logical, efficient, seamless, and interoperable screening workflow. An airport security interoperability data format and communications standard such as Digital Imaging and Communications in Security (DICOS) [1] standard is required to achieve this interoperable security screening workflow. The Transportation Security Administration (TSA) has sponsored open architecture frameworks that will implement several innovative technology solutions. Open standards and architectures will allow for novel technology solutions as new threats are identified, and existing threats evolve. The highlights of the DICOS standard, to meet the requirements of the open architecture, will be explored in this paper.