Alexander Flisch

Gyratory Compaction Analysis with Computer Tomography

ABSTRACT In this study, the change and differences in homogeneity and isotropy in asphalt concrete specimens during gyratory compaction is investigated. The study was carried out by using both standard air-void content determination (AV) and X-ray Computer Tomography (CT), focusing on experimental aspects. It is intended to serve as a basis for laboratories and producers to optimize compaction procedures and devices.

Comparison of Laboratory Compaction Methods using X-ray Computer Tomography

ABSTRACT Changes and differences in homogeneity of asphalt concrete specimens during Marshall and Rolling-Wheel compaction are investigated by means of standard air-void content determination (AV) and X-ray Computer Tomography (CT). Following an earlier study on Gyratory compaction with the same objective and material, this study, again, focuses on experimental aspects serving as a basis for laboratories and producers to optimize compaction procedures and devices. The results demonstrate that X-ray CT is a powerful tool leading to a better understanding of compaction mechanisms. In this way, X-ray CT may be considered very suitable for developing improved laboratory compaction methods and procedures.

New insights into the lifestyle of Allosaurus (Dinosauria: Theropoda) based on another specimen with multiple pathologies

Adult large-bodied theropods are often found with numerous pathologies. A large, almost complete, probably adult Allosaurus specimen from the Howe Stephens Quarry, Morrison Formation (Late Kimmeridgian–Early Tithonian), Wyoming, exhibits multiple pathologies. Pathologic bones include the left dentary, two cervical vertebrae, one cervical and several dorsal ribs, the left scapula, the left humerus, the right ischium, and two left pedal phalanges. These pathologies can be classified as follows: the fifth cervical vertebra, the scapula, several ribs and the ischium are probably traumatic, and a callus on the shaft of the left pedal phalanx II-2 is probably traumatic-infectious. Traumatically fractured elements exposed to frequent movement (e.g., the scapula and the ribs) show a tendency to develop pseudarthroses instead of a callus. The pathologies in the lower jaw and a reduced extensor tubercle of the left pedal phalanx II-2 are most likely traumatic or developmental in origin. The pathologies on the fourth cervical are most likely developmental in origin or idiopathic, that on the left humerus could be traumatic, developmental, infectious or idiopathic, whereas the left pedal phalanx IV-1 is classified as idiopathic. With exception of the ischium, all as traumatic/traumatic-infectious classified pathologic elements show unambiguous evidences of healing, indicating that the respective pathologies did not cause the death of this individual. Alignment of the scapula and rib pathologies from the left side suggests that all may have been caused by a single traumatic event. The ischial fracture may have been fatal. The occurrence of multiple lesions interpreted as traumatic pathologies again underlines that large-bodied theropods experienced frequent injuries during life, indicating an active predatory lifestyle, and their survival perhaps supports a gregarious behavior for Allosaurus. Alternatively, the frequent survival of traumatic events could be also related to the presence of non-endothermic metabolic rates that allow survival based on sporadic food consumption or scavenging behavior. Signs of pathologies consistent with infections are scarce and locally restricted, indicating a successful prevention of the spread of pathogens, as it is the case in extant reptiles (including birds).

Quantitative Untersuchung der Streubeiträge in Hochenergie-Röntgencomputertomografie

Kurzfassung Computertomografie (CT) ist eine bewährte Methode in den Bereichen Fehleranalyse und Qualitätskontrolle. Die Energie der hierbei benutzten Röntgenstrahlung bestimmt die Eindringtiefe der Strahlung und schränkt damit die Grösse und das Material des zu untersuchenden Objektes ein. Für grosse, dichte und schwere Objekte sind Photonenenergien von mehr als einem Megaelektronenvolt (MeV) nötig, um nutzbare Transmissionswerte zu erreichen. Ein wichtiger Faktor für die Qualität hochenergetischer Röntgentomografien ist der Anteil der Streustrahlung auf den CT-Bildern. Röntgenstrahlung kann sowohl im zu untersuchenden Objekt, als auch vom Messinstrument und -umfeld streuen und führt zu einem verfälschten Transmissionsbild. Neben Streueffekten kommt für MeV-Photonen zusätzlich der physikalische Prozess der Paarbildung ins Spiel. Die Auswirkung der einzelnen Streuprozesse auf das Transmissionsbild soll hier untersucht werden. Dafür wird mit Hilfe von Monte-Carlo-Simulationen der Einfluss der verschiedenen Streubeiträge untersucht. Im Gegensatz zu früheren Studien, wird hier nicht nur ein Satz von einfachen geometrischen Objekten aus unterschiedlichen Materialien untersucht, sondern es werden auch vereinfachte Modelle der Komponenten eines CT-Scanners benutzt, um den Beitrag der Streuung verschiedener Systemkomponenten abzuschätzen.

The Use of Industrial Computed Tomography in the Study of Archaeological Finds

The successful use of Computed Tomography (CT) as an efficient and powerful non-destructive tool for the study of archaeological artefacts has been reported by several authors (Rossi et al. 1999a, b; Rossi and Casali 2001; Applbaum and Applbaum 2005). The 3D reconstruction of the objects enables the archaeologists to carry out archaeological analyses; information about manufacturing and assembly techniques, as well as information useful for dating artefacts or determining the appropriate maintenance and restoration procedures can be obtained with this technique (Casali 2006). Most of the studies of archaeological artefacts reported in the literature are carried out using medical CT (Mazansky 1993; Anderson 1995; Allen 2007), whereas investigations performed with industrial CT systems are rather limited. The present study illustrates the results obtained with a high resolution CT system for industrial applications developed in our laboratories. The advantage of our system as compared to medical CT is the higher penetration capability that allows the investigation of high density objects. The system provides isotropic spatial resolution and fast data acquisition due to the cone-beam geometry employed. In this study, we have focused on demonstrating the potential of this procedure for extracting and analysing an item from a cluster. To this aim, we have investigated a ceramic vase with a diameter of 20 cm, filled with ancient coins.

Correction of scattered radiation for cone-beam computed tomography at high X-ray energies

Cone-beam computed tomography (CT) using X-ray tubes of high energy (450 keV) faces the problem of strong artifacts and a significant contrast degradation in reconstructed images. System components of cone-beam CT scanners operating at high X-ray energies have to be optimized to reduce the amount of scattered photons hitting the detector. In addition it is mandatory to apply scatter correction algorithms. A prototype of a cone-beam CT system equipped with a 450 kV industrial X-ray tube has been developed within the framework of a European research project. The influences of scattered radiation generated by the object have been extensively evaluated using Monte Carlo (MC) simulations. Furthermore scattering reduction and correction methods have been developed. A key task was the implementation of a new hybrid method for the fast and accurate calculation of the scattering intensity distribution in X-ray projections for industrial cone-beam CT.

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.

Monte Carlo optimization of an industrial tomography system

Computed tomography (CT) is becoming a very useful non-destructive testing technique, in the industrial field, since it permits the detection of small inner defects in a reliable and accurate way. In order to get very good performance, in terms of image contrast and spatial resolution, the configuration of the tomography system has to be optimized carefully. Monte Carlo simulations can be a very helpful method, for choosing different conditions and selecting the best configuration of a CT system. In this paper we present a preliminary optimization of an industrial CT apparatus, obtained by means of Monte Carlo simulations. The system is composed of an X-ray tube, filtering and collimation devices, and a detector made of a scintillator coupled to a CCD camera. We focus our attention on large aluminum objects and investigate the contribution of the scattered radiation. Some options have been simulated, for reducing the scattering photons, thus improving the overall image quality