Frank Sukowski

Laboratory X-ray microscopy with a nano-focus X-ray source

In this paper we describe the optimization of transmission X-ray targets by Monte-Carlo simulation for a laboratory X-ray microscopy setup. We identified two optimal target layer thicknesses (0.1 μm and 0.7 μm) for a high-resolution target and a high-flux target. Measurements show a decrease in focal spot size by one third or an increase in X-ray flux by a factor of three compared to those of a standard micro-focus target. Focal spot sizes down to 154 nm and 260 nm are achievable with the optimized targets. Simulation results for the X-ray flux match well to the experimental results, whereas the results for the focal spot sizes still show discrepancies attributed to the simplified simulation setup.

Strategies for efficient scanning and reconstruction methods on very large objects with high-energy x-ray computed tomography

X-ray computed tomography (CT) is an established tool for industrial non-destructive testing purposes. Yet conventional CT devices pose limitations regarding specimen dimensions and material thicknesses. Here we introduce a novel CT system capable of inspecting very large objects (VLO) like automobiles or sea freight containers in 3-D and discuss strategies for efficient scanning and reconstruction methods. The system utilizes a 9 MeV linear accelerator to achieve high penetration lengths in both dense and high-Z materials. The line detector array has an overall length of 4 meters. The presented system allows for reconstruction volumes of 3.2 meters in diameter and 5 meters in height. First we outline the general capabilities of high energy CT imaging and compare it with state of the art 450 kV X-ray systems. The imaging performance is shown based on experimental results. The second part addresses the problem of considerably higher scanning times when using line detectors compared to area detectors. Reducing the number of projections considerably causes image artifacts with standard reconstruction methods like filtered back projection (FBP). Alternative methods which can provide significantly better results are algebraic reconstruction techniques (ART). One of these is compressed sensing (CS) based ART which we discuss regarding its suitability in respect to FBP. We could prove the feasibility of inspecting VLOs like complete automobiles based on experimental data. CS allows for achieving sufficient image quality in terms of spatial and contrast resolution while reducing the number of projections significantly resulting in faster scanning times.

Modelling of scintillator based flat-panel detectors with Monte-Carlo simulations

Scintillator based flat panel detectors are state of the art in the field of industrial X-ray imaging applications. Choosing the proper system and setup parameters for the vast range of different applications can be a time consuming task, especially when developing new detector systems. Since the system behaviour cannot always be foreseen easily, Monte-Carlo (MC) simulations are keys to gain further knowledge of system components and their behaviour for different imaging conditions. In this work we used two Monte-Carlo based models to examine an indirect converting flat panel detector, specifically the Hamamatsu C9312SK. We focused on the signal generation in the scintillation layer and its influence on the spatial resolution of the whole system. The models differ significantly in their level of complexity. The first model gives a global description of the detector based on different parameters characterizing the spatial resolution. With relatively small effort a simulation model can be developed which equates the real detector regarding signal transfer. The second model allows a more detailed insight of the system. It is based on the well established cascade theory, i.e. describing the detector as a cascade of elemental gain and scattering stages, which represent the built in components and their signal transfer behaviour. In comparison to the first model the influence of single components especially the important light spread behaviour in the scintillator can be analysed in a more differentiated way. Although the implementation of the second model is more time consuming both models have in common that a relatively small amount of system manufacturer parameters are needed. The results of both models were in good agreement with the measured parameters of the real system.

3-D scanning of sea freight containers using MeV X-rays

The ECSIT project analyses how innovative inspection technologies can lead to an enhanced container security and how these technologies can be embedded into a holistic concept. It has the goal to analyze the possibility and feasibility for 100% scanning of all containers which are shipped to US ports and to develop a concept for integrating necessary infrastructure. A key element of the entire concept is the scanning technology itself. MeV X-ray technology using a linear accelerator as radiation source provides the feasibility to visualize the content of a container without opening it. If a 2-D radiography is ambiguous, a 3-D evaluation of the respective location could be conducted. MeV X-ray computed tomography (CT) is such a method to provide 3-D information of the content of a container. In the context of ECSIT, Fraunhofer EZRT has developed the concept of such a continuative high energy X-ray scanning stage and evaluated its application to sea freight containers. In this paper different approaches for measuring a 3-D tomographic volume data set of objects which are very heavy and thus difficult to move in arbitrary directions will be discussed. Three different geometrical principles for data acquisition were evaluated: laminography, limited angle CT, and a gantry CT. The volume data sets were reconstructed by using a standard filtered back projection and different algebraic reconstruction techniques (ART). Real 3-D volume data of large objects measured with the set-up described above are presented. As test objects a real container packed with various typical goods like furniture or consumer electronics as well as simulated threats like a bomb mock-up was used.

Simulation study of a highly efficient, high resolution X-ray sensor based on self-organizing aluminum oxide

State of the art X-ray imaging sensors comprise a trade-off between the achievable efficiency and the spatial resolution. To overcome such limitations, the use of structured and scintillator filled aluminum oxide (AlOx) matrices has been investigated. We used Monte-Carlo (MC) X-ray simulations to determine the X-ray imaging quality of these AlOx matrices. Important factors which influence the behavior of the matrices are: filling factor (surface ratio between channels and `closed` AlOx), channel diameter, aspect ratio, filling material etc. Therefore we modeled the porous AlOx matrix in several different ways with the MC X-ray simulation tool ROSI [1] and evaluated its properties to investigate the achievable performance at different X-ray spectra, with different filling materials (i.e. scintillators) and varying channel height and pixel readout. In this paper we focus on the quantum efficiency, the spatial resolution and image homogeneity.

Creating a reference database of cargo inspection X-ray images using high energy CT of cargo mock-ups

Customs continue to use a wide range of technology in protecting against terrorism and the movement of illicit trade and prohibited imports. The throughput of scanned vehicles and cargo increases and just keeps on growing. Therefore, the need of automated algorithms to help screening officers in inspection, examination or surveillance of vehicles and containers is crucial. In this context, the successful collaboration between manufacturers and customs offices is of key importance. Facing this topic, within the seventh framework program of the European Commission, the project ACXIS “Automated Comparison of X-ray Images for cargo Scanning” arose. The main objective of this project is to develop a manufacturer independent reference database for X-ray images of illicit and licit cargo. Historic images of real detections, images of illegal cargo mock-ups as well as images of legitimate cargo will be integrated into the reference database. For this, procedures and algorithms to uniform X-ray images of different cargo scanners was developed, as well as an automated identification method of potentially illicit cargo. Finally, these developments were incorporated in creating a training simulator and a toolbox for inspection officers enhanced X-ray screening competence.

Recent progress in 3-D imaging of sea freight containers

The inspection of very large objects like sea freight containers with X-ray Computed Tomography (CT) is an emerging technology. A complete 3-D CT scan of a see-freight container takes several hours. Of course, this is too slow to apply it to a large number of containers. However, the benefits of a 3-D CT for sealed freight are obvious: detection of potential threats or illicit cargo without being confronted with legal complications or high time consumption and risks for the security personnel during a manual inspection. Recently distinct progress was made in the field of reconstruction of projections with only a relatively low number of angular positions. Instead of today’s 500 to 1000 rotational steps, as needed for conventional CT reconstruction techniques, this new class of algorithms provides the potential to reduce the number of projection angles approximately by a factor of 10. The main drawback of these advanced iterative methods is the high consumption for numerical processing. But as computationa...

Developing a Compton spectrometer for determination of X-ray tube spectra

In medical applications and non-destructive testing, knowledge of emitted X-ray spectra of X-ray tubes can be of great importance, e.g. for quality control issues or material decomposition techniques. Conventional methods of measuring spectra with a photon counting detector positioned in the primary beam often show unsatisfactory results, especially when applying high flux in conjunction with high X-ray eYXB3-01138-A461nergies (above 100 keV). The two main problems arising are pulse pile up, i.e. the impossibility to differentiate between multiple photons in one readout interval, and the reduced detector efficiency at high X-ray energies because of limited sensor thickness. These effects lead to significant errors in the determination of X-ray tube spectra. To overcome these limitations we built a Compton spectrometer based on the Compton spectroscopy approach by Yaffe et al.

Monte Carlo Simulations in NDT

X-ray techniques are commonly used in the fields of non-destructive testing (NDT) of industrial parts, material characterization, security and examination of various other specimens. The most used techniques for obtaining images are radioscopy for 2D and computed tomography (CT) for 3D imaging. Apart from these two imaging techniques, where X-ray radiation penetratesmatter, other methods like refraction or fluorescence analysis can also be used to obtain information about objects and materials. The vast diversity of possible specimen and examination tasks makes the development of universal X-ray devices impossible. It rather is necessary to develop and optimize X-ray machines for a specific task or at least for a limited range of tasks. The most important parameters that can be derived from object geometry and material composition are the X-ray energy or spectrum, the dimensions, the examination geometries and the size of the detector. The task itself demands a certain image quality which depends also on the X-ray spectrum, the examination geometry and furthermore on the size of the X-ray source’s focal spot and the resolution of the detector. Monte-Carlo (MC) simulations are a powerful tool to optimize an X-ray machine and its key components. The most important components are the radiation source, e.g. an X-ray tube and the detector. MC particle physics simulation codes like EGS (Nelson et al., 1985) or GEANT (Agostinelli et al., 2003) can describe all interactions of particles with matter in an X-ray environment verywell. Almost all effects can be derived from these particle physics processes. The MC codes are event based. Every single primary particle is generated and tracked along with all secondary particles until the energy of all particles drops below a certain threshold. The primaries are generated one after another, since no interactions between particles take place. When simulating X-ray sources, in most cases X-ray tubes, the primary particles are electrons. The electron beam is parameterized by the electrons’ kinetic energy and the intensity profile along the cross-section of the beam. When hitting the target, X-rays are generated by interaction of electrons with the medium. The relevant magnitudes for imaging are the X-ray energy spectrum and the effective optical focal spot size (Morneburg, 1995). The most used imaging systems in the field of NDT are flat panel detectors. There are two basic types of detectors: Direct converting semiconductor detectors and indirect converting scintillation detectors. The type of particle interactions in the respective sensor layer determines the detection efficiency and effective spatial resolution. Interaction of X-rays in direct converting detectors produces electron-hole-pairs in the semiconductor materials. The free charge carriers drift to electrodes,where the current can bemeasured.MC simulations can Monte Carlo Simulations in NDT

Measurement of shafts in the production process based on x-rays

Production metrology faces challenges connected to the production industry where consumers of products expect a standard of high quality at inexpensive costs. One approach for the next generation of production metrology devices aims at ensuring the quality of the process technologies in every single process step, therefore measuring in-process. One example of todays production metrology devices is the measurement of shafts in the production. Shafts are vital for every mechanical device that translates rotational energies and the tolerances based on diameter or roundness are in the range of microns. Those shaft measurement devices are either based on tactile measurements or on visible light which cannot be utilized as an in-process device. A novel idea is to use X-rays instead of tactile or visible light methods to be able to acquire robust measurement data despite of distorting debris like water, oil or dust. One focus is set on algorithms that allow robust measurements of diameter and roundness despite of distorting debris like water, oil or dust. The measurement uncertainty of the new method has been investigated and results will be introduced.