Partially Coherent Lab Based X-ray Micro Computed Tomography

X-ray micro computed tomography (CT) is a useful tool for imaging 3-D internal structures. It has many applications in geophysics, biology and materials science. Currently, micro-CT’s capability are limited due to validity of assumptions used in modelling the machines’ physical properties, such as penumbral blurring due to non-point source, and X-ray refraction. Therefore many CT research in algorithms and models are being carried out to overcome these limitations. This thesis presents methods to improve image resolution and noise, and to enable material property estimation of the micro-CT machine developed and in use at the ANU CTLab. This thesis is divided into five chapters as outlined below. The broad background topics of X-ray modelling and CT reconstruction are explored in Chapter 1, as required by later chapters. It describes each X-ray CT component, including the machines used at the ANU CTLab. The mathematical and statistical tools, and electromagnetic physical models are provided and used to characterise the scalar X-ray wave. This scalar wave equation is used to derive the projection operator through matter and free space, and basic reconstruction and phase retrieval algorithms. It quantifies the four types of X-ray interaction with matter for X-ray energy between 1 and 1000 keV, and presents common assumptions used for the modelling of lab based X-ray micro-CT. Chapter 2 is on X-ray source deblurring. The penumbral source blurring for X-ray micro-CT systems are limiting its resolution. This chapter starts with a geometrical framework to model the penumbral source blurring. I have simulated the effect of source blurring, assuming the geometry of the high-cone angle CT system, used at the ANU CTLab. Also, I have developed the Multislice Richardson-Lucy method that overcomes the computational complexity of the conjugate gradient method, while produces less artefacts compared to the standard Richardson-Lucy method. Its performance is demonstrated for both simulated and real experimental data. X-ray refraction, phase contrast and phase retrieval (PR) are investigated in Chapter 3. For weakly attenuating samples, intensity variation due to phase contrast is a significant fraction of the total signal. If phase contrast is incorrectly modelled, the reconstruction would not correctly account the phase contrast, therefore it would contribute to undesirable artefacts in the reconstruction volume. Here I present a novel Linear Iterative multi-energy PR algorithm. It enables material property estimation for the near field submicron X-ray CT system and reduces the noise and artefacts. This PR algorithm expands the validity range in comparison to the single material and data constrained modelling methods. I have also extended this novel PR algorithm to assume a polychromatic incident spectrum for a non-weakly absorbing object. Chapter 4 outlines the space filling X-ray source trajectory and reconstruction, on which I contributed in a minor capacity. This space filling trajectory reconstruction have improved the detector utilisation and reduced nonuniform resolution over the state-of-the-art 3-D Katsevich’s helical reconstruction, this patented work was done in collaboration with FEI Company. Chapter 5 concludes my PhD research work and provides future directions revealed by the present research

Realistic rendering and reconstruction of astronomical objects and an augmented reality application for astronomy

These days, there is an ever increasing need for realistic models, renderings and visualization of astronomical objects to be used in planetarium and as a tool in modern astrophysical research. One of the major goals of this dissertation is to develop novel algorithms for recovering and rendering 3D models of a specific set of astronomical objects. We first present a method to render the color and shape of the solar disc in different climate conditions as well as for different height to temperature atmospheric profiles. We then present a method to render and reconstruct the 3D distribution of reflection nebulae. The rendering model takes into account scattering and absorption to generate physically realistic visualization of reflection nebulae. Further, we propose a reconstruction method for another type of astronomical objects, planetary nebulae. We also present a novel augmented reality application called the augmented astronomical telescope, tailored for educational astronomy. The real-time application augments the view through a telescope by projecting additional information such as images, text and video related to the currently observed object during observation. All methods previously proposed for rendering and reconstructing astronomical objects can be used to create novel content for the presented augmented reality application.Realistische Modelle, Visualisierungen und Renderings von astronomischen Objekten gewinnen heuzutage in Planetarium Shows oder als Werkzeug für die Astrophysikalische Forschung immer mehr an Bedeutung. Eines der Hauptziele dieser Dissertation ist es, neue Algorithmen zum Rendering und zur Rekonstruktion von Astronomischen Objekten zu entwickeln. Wir beschreiben zuerst ein Verfahren zum Rendering von Farbe und Form der Sonnenscheibe für verschiedene Klimate und gegebenen Höhe zu Temperatur Profilen. Im weiterem wird eine Methode zum Rendering und zur Rekonstruktion von 3D Modellen von Reflexionsnebeln präsentiert. Das Renderingmodell berücksichtigt Streuung und Absorption, um physikalisch realistische Visualisierungen von Reflexionsnebeln zu erzeugen. Weiter, wird ein Rekonstruktionsalgorithmus für eine andere Art astronomischer Objekte, Planetarische Nebel, vorgeschlagen. Wir stellen eine neuartige Erweiterte Realität Anwendung vor, welche für die astronomische Bildung zugeschnitten ist. Die Anwedung erweitert die Sicht durch das Okular des Teleskopes und projiziert zusätzliche Informationen wie Bilder, Text und Video online, während des Betrachtens. Alle vorher erwähnten Verfahren zum Rendering und zur Rekonstruktion von Astronomischen Objekten können verwendet werden, um Inhalte für die vorgestellte Erweiterte Realität Anwendung zu entwerfen

Realistic rendering and reconstruction of astronomical objects and an augmented reality application for astronomy

These days, there is an ever increasing need for realistic models, renderings and visualization of astronomical objects to be used in planetarium and as a tool in modern astrophysical research. One of the major goals of this dissertation is to develop novel algorithms for recovering and rendering 3D models of a specific set of astronomical objects. We first present a method to render the color and shape of the solar disc in different climate conditions as well as for different height to temperature atmospheric profiles. We then present a method to render and reconstruct the 3D distribution of reflection nebulae. The rendering model takes into account scattering and absorption to generate physically realistic visualization of reflection nebulae. Further, we propose a reconstruction method for another type of astronomical objects, planetary nebulae. We also present a novel augmented reality application called the augmented astronomical telescope, tailored for educational astronomy. The real-time application augments the view through a telescope by projecting additional information such as images, text and video related to the currently observed object during observation. All methods previously proposed for rendering and reconstructing astronomical objects can be used to create novel content for the presented augmented reality application.Realistische Modelle, Visualisierungen und Renderings von astronomischen Objekten gewinnen heuzutage in Planetarium Shows oder als Werkzeug für die Astrophysikalische Forschung immer mehr an Bedeutung. Eines der Hauptziele dieser Dissertation ist es, neue Algorithmen zum Rendering und zur Rekonstruktion von Astronomischen Objekten zu entwickeln. Wir beschreiben zuerst ein Verfahren zum Rendering von Farbe und Form der Sonnenscheibe für verschiedene Klimate und gegebenen Höhe zu Temperatur Profilen. Im weiterem wird eine Methode zum Rendering und zur Rekonstruktion von 3D Modellen von Reflexionsnebeln präsentiert. Das Renderingmodell berücksichtigt Streuung und Absorption, um physikalisch realistische Visualisierungen von Reflexionsnebeln zu erzeugen. Weiter, wird ein Rekonstruktionsalgorithmus für eine andere Art astronomischer Objekte, Planetarische Nebel, vorgeschlagen. Wir stellen eine neuartige Erweiterte Realität Anwendung vor, welche für die astronomische Bildung zugeschnitten ist. Die Anwedung erweitert die Sicht durch das Okular des Teleskopes und projiziert zusätzliche Informationen wie Bilder, Text und Video online, während des Betrachtens. Alle vorher erwähnten Verfahren zum Rendering und zur Rekonstruktion von Astronomischen Objekten können verwendet werden, um Inhalte für die vorgestellte Erweiterte Realität Anwendung zu entwerfen

Image Restoration

This book represents a sample of recent contributions of researchers all around the world in the field of image restoration. The book consists of 15 chapters organized in three main sections (Theory, Applications, Interdisciplinarity). Topics cover some different aspects of the theory of image restoration, but this book is also an occasion to highlight some new topics of research related to the emergence of some original imaging devices. From this arise some real challenging problems related to image reconstruction/restoration that open the way to some new fundamental scientific questions closely related with the world we interact with

Development and Characterization of a Fast Neutron Imaging Telescope (FNIT) for 1--20 MeV Neutrons From the Sun and Nuclear Material

We discuss the development and complete characterization of a double scatter telescope for 1--20 MeV neutrons intended for applications in solar physics and nuclear security. In high-energy solar physics, detecting the presence of low energy accelerated ions in the low corona is recognized as an important goal. The surest indication of the acceleration of these particles is the detection of low energy (\u3c10 MeV) neutrons. These measurements can only be made in the inner heliosphere due to the finite neutron lifetime and flux divergence as they leave the Sun. Additionally, the field of nuclear security has interest in an instrument that can detect, measure, and locate sources of (\u3c10 MeV) neutrons from nuclear material. Materials of interest, namely uranium and transuranics, emit neutrons via spontaneous or induced fission. Unlike other neutral emission from nuclear material, (e.g. gamma rays), copious and penetrating neutron emission is unique to fissionable material. The FNIT instrument was carefully tailored for both applications with a low energy threshold. A double scatter instrument allows for background rejection techniques to obtain increased sensitivity. A small, modular prototype instrument was constructed at UNH with laboratory calibration completed to tune the pulse height and shape, threshold, and time-of-flight for neutron measurements. Quasi-monoenergetic neutron beams calibrated the prototype over the full energy range and fission neutrons were used to test the response and performance of the instrument. Simulations characterized the instrument energy response and were used to generate response matrices for data inversion. We used zeroth-order Tikhonov regularization de-convolution algorithms to obtain the true neutron source spectrum for a given regularization (smoothing) parameter, lambda. Independent of the binning strategy, lambda is of order 10-6. We find that lambda +/- sigma results in a 2% error in total neutron counts; an error within +/-5-sigma results in a variation of ≤ 30% in total neutron counts. Double scatter imaging, adopted from gamma-ray telescopes, demonstrate source location identification can be obtained. We apply laboratory and simulation information to obtain performance estimates of future instruments near the Sun and in the field