Design, development and characterization of a novel neutron and X-ray combined computed tomography system

Visualizing the three dimensional structure of objects (e.g. nuclear fuel, nuclear materials, explosives and bio materials) and phenomena (e.g. particle tracking) can be very important in nondestructive testing applications. Computed tomography systems are indispensable tools for these types of applications because they provide a versatile non-destructive technique for analysis. A novel neutron and X-ray combined computed tomography (NXCT) system has been designed and developed at the Missouri University of Science & Technology. The neutron and X-ray combined computed tomography system holds much promise for non-destructive material detection and analysis where multiple materials having similar atomic number and differing thermal cross section or vice versa may be present within an object, exclusive neutron or X-ray analysis may exhibit shortcomings in distinguishing interfaces. However, fusing neutron image and X-ray image offers the strengths of both and may provide a superior method of analysis. In addition, a feasible design of a sample positioning system which allows the user to remotely and automatically manipulate the objects makes the NXCT system viable for commercial applications. Moreover, characterization of the newly developed digital imaging system is imperative to the performance evaluation, as well as for describing the associated parameters. The performance of a combined neutron/X-ray digital imaging system was evaluated in terms of modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE). This dissertation is a complete overview of the design of the NXCT system, operation, algorithms, performance evaluation and results --Abstract, page iii

Medical computed tomography (CT) able to image the past: an investigation of diagnostic accuracy and image quality

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg, South Africa, May 2018.The use of X-ray imaging in palaeoanthropology has a long history. Both plain X- rays as well as computed tomography have successfully imaged fossils that have been cleaned and prepared from any encasing materials. There has, however, been very little work done using radiological techniques to image fossils still enclosed in surrounding matrix. Most imaging modalities have been applied post preparation of the fossils. This body of work explores the use of medical computed tomography (XCT) in the pre-preparatory phase of fossil discovery in the South African context. Scanning of breccia blocks from the site of Malapa on XCT concluded that the resultant images were of sufficient quality to enable accurate fossil identification and characterization when measured against the standard of manual preparation. Breccia blocks from Malapa were scanned at high and lower energies using micro CT (μXCT) and XCT respectively. Images were analysed for image quality, artifact and certainty of diagnosis. Results show that lower energy images are deemed superior to higher energy images for this particular application. This finding, taken together with the limitations associated with the use of μXCT for the imaging of the large breccia from Malapa, shows that XCT is the better modality for this specific application. Pre-preparatory XCT scanning can focus both preparation and interpretation of findings. The importance of pre-preparatory XCT imaging is demonstrated by the fact that preparatory techniques and protocols need to be modified from traditional methods in order to minimize the risk of contamination of possible biomolecules. Revision is needed of the peri and post excavation treatment of fossil bones to better preserve the potential of genetic heritage of the past and this research demonstrates the role that XCT can play. None of the research covered by this body of work has been done before on fossil- bearing matrices. This research should significantly change the way fossil discovery, recovery and preparation is done in the South African context and has potential for application in other palaeontological situations.LG201

Combined fast neutron - gamma ray computed tomography and radiography

The combination of real-time fast-neutron and γ-ray assessment for the purpose of tomography and radiography has been investigated using a number of complementary experimental techniques. The research described in this thesis comprises an extensive Monte Carlo simulation study and three experimental approaches, each of which is supported by computer simulations themselves. In the Monte Carlo study, computed by means of MCNP6, actinide materials such as plutonium metal, plutonium oxide, uranium metal, U3O8 and UC2, have been shielded with combinations of lead and high-density polyethylene, then investigated actively with a simulated beam of both fast neutrons and γ rays produced by an americium-beryllium source, and detected by an array of liquid scintillation detectors. This Monte Carlo study demonstrates that, in terms of relative image contrast, the combination of γ and neutron tomography yields to a better discrimination amongst plutonium metal, lead and polyethylene, as well as amongst uranium-based compounds, such as uranium metal and uranium carbide, with the same shielding materials. Less convincing contrast is instead obtained when plutonium oxide and U3O8 are concealed with the same shielding arrangement of lead and polyethylene. The study also shows that a combination of both fast neutron and γ radiation, in several cases, led to a better spatial resolution (order of a few mm) of that achieved using fast neutrons or γ rays in isolation. A similar approach was performed to investigate a variety of materials often associated with conventional explosives and a lithium-based polymer (LiPo). By means of neutron tomography, LiPo and water, hydrogen peroxide, acetone, RDX, TNT, NC have been discerned from one another; whilst the γ tomography approach helps to discern, for instance, RDX from acetone. Experimentally, this technique has been computed, albeit in terms of radiography rather than tomography, using a californium neutron source and single scintillation detector coupled to a real-time, pulse-shape discrimination system. A lithium ion laptop battery was scanned and compared with an X-ray radiograph of the battery itself. These experimental results show that the combined neutron-γ imaging spatial information is comparable to what obtained with the X-ray. In addition, the results show that higher level of image contrast is present in the proximity of the cell batteries, suggesting the potential to identify the spatial lithium polymer distribution within the cell batteries. Furthermore, an alternative approach to investigate a single material type subject to changes in dimension, hypothetically due to corrosion, has been explored. This was conducted assessing both the fast neutron and γ ray flux backscattered by irradiated steel slabs, as a function of their thickness. Such research, carried out with the objective to detect flaws in pipeline sections, not only showed the potential to estimate different thicknesses of steel in isolation, but also showed the potential to measure thicknesses of slabs covered by a layer of materials commonly used for pipelines insulation, such as polyethylene and concrete. Finally, a Monte Carlo study has been completed for an arrangement in which a particle accelerator has been used as the neutron source, with which to explore the potential benefits of combining high-resolution γ-ray spectroscopy, neutron tomography and γ-ray tomography in the same approach. The outcome of this study showed the possibility to identify and localise the distribution of different isotopes of metals, such as 56Fe and 63Cu in a sample. The research presented associated with this aspect of the thesis has potential applications in nuclear safeguards, homeland security, contraband detection and in fields where relatively quick and non-destructive inspections are needed

Aiding the conservation of two wooden Buddhist sculptures with 3D imaging and spectroscopic techniques

The conservation of Buddhist sculptures that were transferred to Europe at some point during their lifetime raises numerous questions: while these objects historically served a religious, devotional purpose, many of them currently belong to museums or private collections, where they are detached from their original context and often adapted to western taste. A scientific study was carried out to address questions from Museo d'Arte Orientale of Turin curators in terms of whether these artifacts might be forgeries or replicas, and how they may have transformed over time. Several analytical techniques were used for materials identification and to study the production technique, ultimately aiming to discriminate the original materials from those added within later interventions

Investigation of Delayed Ettringite Formation Damage Process Using Simultaneous Neutron and X-ray Tomography

Delayed ettringite formation (DEF) is a significant deterioration process in concrete which involves the growth of ettringite [Ca6Al2(SO4)3(OH)12 ·26H2O] crystals leading to cracking and reduction of compressive strength. Conditions leading to DEF are well known and include among others cement chemistry, presence of humidity, heat curing of concrete structures, and the presence of cracks. The mechanisms and kinetics by which deterioration occur is still not well understood despite numerous investigations. Understanding the mechanism and kinetics of concrete deterioration due to DEF is important in order to prevent such costly deterioration and to improve concrete durability. In this research, concrete specimens were prepared with type III Portland cement and under different conditions that were designed to either promote or inhibit DEF. These consisted of a control set, a set subjected to a heat cycle and a third set made with elevated potassium content of 1.72% and also thermally cycled. They were tested periodically up to 380 days by conventional methods such as expansion and weight change measurements and compressive strength testing. Scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDAX) confirmed the presence and the morphology of ettringite in voids at different ages. Simultaneous neutron and X-ray tomography, a new nondestructive microscopic method was used to scan the specimens at regular intervals in order to assess the feasibility of the method in monitoring the progress and characterizing DEF induced damages. The linear regression analysis of the correlation of expansion with weight change data revealed that expansion and deterioration process occurred in three distinct successive stages. In the first stage, the ettringite fills the pores with little or no expansion; in the second, the expansion appears to be creep due to expansive stresses in the filled pores and in the third stage, crack propagation leads to significant expansion and loss of compressive strength. The results of the linear regression also revealed that the mechanism of DEF is the replacement of pre-existing calcium hydroxide crystals. Through non-linear curve fitting, the kinetic of deterioration was modeled using the Kolmogorov-Avrami-Johnson-Miehl model. The simultaneous neutron and X-ray tomography allowed visualization of the interior of the specimen due to enhance phase segmentation. MATLAB routines were developed to allow for correction for beam hardening and to enhance phase segmentation. The study showed that with improved resolution, proper sample sizing, the method can be effectively used to characterize concrete damage due to expansive phases

A multi-technique hierarchical X-ray phase-based approach for the characterization and quantification of the effects of novel radiotherapies

Cancer is the first or second leading cause of premature deaths worldwide with an overall rapidly growing burden. Standard cancer therapies include surgery, chemotherapy and radiotherapy (RT) and often a combination of the three is applied to improve the probability of tumour control. Standard therapy protocols have been established for many types of cancers and new approaches are under study especially for treating radio-resistant tumours associated to an overall poor prognosis, as for brain and lung cancers. Follow up techniques able to monitor and investigate the effects of therapies are important for surveying the efficacy of conventionally applied treatments and are key for accessing the curing capabilities and the onset of acute and late adverse effects of new therapies. In this framework, this doctoral Thesis proposes the X-ray Phase Contrast Im-aging - Computed Tomography (XPCI-CT) technique as an imaging-based tool to study and quantify the effects of novel RTs, namely Microbeam and Minibeam Radiation therapy (MRT and MB), and to compare them to the standard Broad Beam (BB) induced effects on brain and lungs. MRT and MB are novel radiotherapies that deliver an array of spatially fractionated X-ray beamlets issued from a synchrotron radiation source, with widths of tens or hundreds of micrometres, respectively. MRT and MB exploit the so-called dose-volume effect: hundreds of Grays are well tolerated by healthy tissues and show a preferential effect on tumour cells and vasculature when delivered in a micrometric sized micro-plane, while induce lethal effects if applied over larger uniform irradiation fields. Such highly collimated X-ray beams need a high-resolution and a full-organ approach that can visualize, with high sensitivity, the effects of the treatment along and outside the beamlets path. XPCI-CT is here suggested and proven as a powerful imaging technique able to determine and quantify the effects of the radiation on normal and tumour-bearing tissues. Moreover, it is shown as an effective technique to complement, with 3D information, the histology findings in the follow-up of the RT treatments. Using a multi-scale and multi-technique X-ray-based approach, I have visualized and analysed the effects of RT delivery on healthy and glioblastoma multiforme (GBM)-bearing rat brains as well as on healthy rat lungs. Ex-vivo XPCI-CT datasets acquired with isotropic voxel sizes in the range 3.253 – 0.653 μm3 could distinguish, with high sensitivity, the idiopathic effects of MRT, MB and BB therapies. Histology, immunohistochemistry, Small- and Wide-Angle X-ray Scattering and X-ray Fluorescence experiments were also carried out to accurately interpret and complement the XPCI-CT findings as well as to obtain a detailed structural and chemical characterization of the detected pathological features. Overall, this multi-technique approach could detect: i) a different radio-sensitivity for the MRT-treated brain areas; ii) Ca and Fe deposits, hydroxyapatite crystals formation; iii) extended and isolated fibrotic contents. Full-organ XPCI-CT datasets allowed for the quantification of tumour and mi-crocalcifications’ volumes in treated brains and the amount of scarring tissue in irradiated lungs. Herein, the role of XPCI-CT as a 3D virtual histology technique for the follow-up of ex-vivo RT effects has been assessed as a complementary method for an accurate volumetric investigation of normal and pathological states in brains and lungs, in a small animal model. Moreover, the technique is proposed as a guidance and auxiliary tool for conventional histology, which is the gold standard for pathological evaluations, owing to its 3D capabilities and the possibility of virtually navigating within samples. This puts a landmark for XPCI-CT inclusion in the pre-clinical studies pipeline and for advancing towards in-vivo XPCI-CT imaging of treated organs.Weltweit gilt Krebs als häufigste bzw. zweithäufigste Ursache eines zu früh erfolgenden Todes, wobei die Zahlen rasch ansteigen. Standardmäßige Krebstherapien umfassen chirurgische Eingriffe, Chemotherapie und Strahlentherapie (radiotherapy, RT); oft kommt eine Kombination daraus zur Anwendung, um die Wahrscheinlichkeit der Tumorkontrolle zu erhöhen. Es wurden Standardtherapieprotokolle für zahlreiche Krebsarten eingerichtet und es wird vor allem in der Behandlung von strahlenresistenten Tumoren mit allgemein schlechter Prognose wie bei Hirn- und Lungentumoren an neuen Ansätzen geforscht. Nachverfolgungstechniken, welche die Auswirkungen von Therapien überwachen und ermitteln, sind zur Überwachung der Wirksamkeit herkömmlich angewandter Behandlungen wichtig und auch maßgeblich am Zugang zu den Fähigkeiten zur Heilung sowie zum Auftreten akuter und verzögerter Nebenwirkungen neuer Therapien beteiligt. In diesem Rahmenwerk unterbreitet diese Doktorarbeit die Technik der Röntgen-Phasenkontrast-Bildgebung über Computertomographie (X-ray Phase Contrast Imaging - Computed Tomography, XPCI‑CT) als bildverarbeitungs-basiertes Tool zur Untersuchung und Quantifizierung der Auswirkungen neuartiger Strahlentherapien, nämlich der Mikrobeam- und Minibeam-Strahlentherapie (MRT und MB), sowie zum Vergleich derselben mit den herkömmlichen durch Breitstrahlen (Broad Beam, BB) erzielten Auswirkungen auf Gehirn und Lunge. MRT und MB sind neuartige Strahlentherapien, die ein Array räumlich aufgeteilter Röntgenstrahlenbeamlets aus einer synchrotronen Strahlenquelle mit einer Breite von Zehnteln bzw. Hundersteln Mikrometern abgeben. MRT und MB nutzen den sogenannten Dosis-Volumen-Effekt: Hunderte Gray werden von gesundem Gewebe gut vertragen und wirken bei der Abgabe in einer Mikroebene im Mikrometerbereich vorrangig auf Tumorzellen und Blutgefäße, während sie bei einer Anwendung über größere gleichförmige Strahlungsfelder letale Auswirkungen aufweisen. Solche hoch kollimierten Röntgenstrahlen erfordern eine hohe Auflösung und einen Zugang zum gesamten Organ, bei dem die Auswirkungen der Behandlung entlang und außerhalb der Beamletpfade mit hoher Empfindlichkeit visualisiert werden können. Hier empfiehlt und bewährt sich die XPCI‑CT als leistungsstarke Bildverarbeitungstechnik, welche die Auswirkungen der Strahlung auf normale und tumortragende Gewebe feststellen und quantifizieren kann. Außerdem hat sich gezeigt, dass sie durch 3‑D-Informationen eine effektive Technik zur Ergänzung der histologischen Erkenntnisse in der Nachverfolgung der Strahlenbehandlung ist. Anhand eines mehrstufigen und multitechnischen röntgenbasierten Ansatzes habe ich die Auswirkungen der Strahlentherapie auf gesunde und von Glioblastomen (GBM) befallene Rattenhirne sowie auf gesunde Rattenlungen visualisiert und analysiert. Mit isotropen Voxelgrößen im Bereich von 3,53 bis 0,653 μm3 erfasste Ex-vivo-XPCI-CT-Datensätze konnten die idiopathischen Auswirkungen der MRT-, MB- und BB‑Behandlung mit hoher Empfindlichkeit unterscheiden. Es wurden auch Experimente zu Histologie, Immunhistochemie, Röntgenklein- und ‑weitwinkelstreuung und Röntgenfluoreszenz durchgeführt, um die XPCI‑CT-Erkenntnisse präzise zu interpretieren und zu ergänzen sowie eine detaillierte strukturelle und chemische Charakterisierung der nachgewiesenen pathologischen Merkmale zu erhalten. Im Allgemeinen wurde durch diesen multitechnischen Ansatz Folgendes ermittelt: i) eine un-terschiedliche Strahlenempfindlichkeit der mit MRT behandelten Gehirnbereiche; ii) Ca- und Fe-Ablagerungen und die Bildung von Hydroxylapatitkristallen; iii) ein ausgedehnter und isolierter Fibrosegehalt. XPCI‑CT-Datensätze des gesamten Organs ermöglichten die Quantifizierung der Volume von Tumoren und Mikroverkalkungen in den behandelten Gehirnen und der Menge des Narbengewebes in bestrahlten Lungen. Dabei wurde die Rolle der XPCI‑CT als virtuelle 3‑D-Histologietechnik für die Nachverfolgung von Ex-vivo-RT‑Auswirkungen als ergänzende Methode für eine präzise volumetrische Untersuchung des normalen und pathologischen Zustands von Gehirnen und Lungen im Kleintiermodell untersucht. Darüber hinaus wird die Technik aufgrund ihrer 3‑D-Fähigkeiten und der Möglichkeit zur virtuellen Navigation in den Proben als Leitfaden und Hilfstool für die herkömmliche Histologie vorgeschlagen, die der Goldstandard für die pathologische Evaluierung ist. Dies markiert einen Meilenstein für die Übernahme der XPCI‑CT in die Pipeline präklinischer Studien und für den Übergang zur In-vivo-XPCI‑CT von behandelten Organen