Jeffrey R. Schubert

X-ray backscatter imaging

In contrast to transmission X-ray imaging systems where inspected objects must pass between source and detector, Compton backscatter imaging allows both the illuminating source as well as the X-ray detector to be on the same side of the target object, enabling the inspection to occur rapidly and in a wide variety of space-constrained situations. A Compton backscatter image is similar to a photograph of the contents of a closed container, taken through the container walls, and highlights low atomic number materials such as explosives, drugs, and alcohol, which appear as especially bright objects by virtue of their scattering characteristics. Techniques for producing X-ray images based on Compton scattering will be discussed, along with examples of how these systems are used for both novel security applications and for the detection of contraband materials at ports and borders. Differences between transmission and backscatter images will also be highlighted. In addition, tradeoffs between Compton backscatter image quality and scan speed, effective penetration, and X-ray source specifications will be discussed.

Sparse view Compton scatter tomography with energy resolved data: experimental and simulation results

X-ray inspection systems play a critical role in many non-destructive testing and security applications, with systems typically measuring attenuation during transmission along straight-line paths connecting sources and detectors. Computed tomography (CT) systems can provide higher-quality images than single- or dual-view systems, but the need to measure many projections through the scene increases system complexity and cost. We seek to maximize the image quality of sparse-view (few-view) systems by combining attenuation data with measurements of Compton-scattered photons, that deflect after scattering and arrive at detectors via broken ray paths that provide additional sampling of the scene. The work below presents experimental validation of a singlescatter forward model for Compton-scatter data measured with energy-resolving detectors, and demonstrates a reconstruction algorithm that combines both attenuation and scatter measurements. The results suggest that including Compton-scattered data in the reconstruction process can improve image quality for few-view systems.

Rapid inspection of general aviation aircraft for security threats and contraband

In the US, inbound international general aviation flights need to be inspected daily. The objects of interest include explosives, weapons, currency, and contraband. An imaging system capable of seeing through the skin of the aircraft to identify suspicious items would considerably speed up the inspection process. For inspection of shipping containers, cars, trucks, and other vehicles, AS&E has fielded many hundreds of X-ray backscatter systems composed mostly of the Z Backscatter® Van and the Z Portal® system. Due to their complicated shapes, large variation in profiles and sizes, and particular operational settings, aircraft require a specialized type of scanner which has been developed by AS&E. Initial feasibility experiments have demonstrated that the X-ray backscatter method is very effective for detecting objects of interest inside aircraft of different types and sizes. Analysis of images illustrating the imaging tradeoffs is presented. In designing a product for this task the challenges are not limited to X-ray imaging. Due to operational issues, special considerations are needed for collision avoidance, zero-turn-radius, shape-following scanning, adaptive detection area, and video overlay. This paper details the requirements and tradeoffs involved in the system design, along with an overview of the prototype and its performance.