Partially Coherent Lab Based X-ray Micro Computed Tomography

dc.contributor.authorLi, Heyang (Thomas)en_AU
dc.date.accessioned2017-04-30T23:35:53Z
dc.date.available2017-04-30T23:35:53Z
dc.date.issued2016
dc.description.abstractX-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.en_AU
dc.identifier.otherb43751702
dc.identifier.urihttp://hdl.handle.net/1885/116224
dc.language.isoenen_AU
dc.subjectmicro computed tomographyen_AU
dc.subjectpenumbral blurringen_AU
dc.subjectnon-point sourceen_AU
dc.subjectX-ray refractionen_AU
dc.subjectCT researchen_AU
dc.subjectANU CTLaben_AU
dc.subjectX-ray modellingen_AU
dc.subjectCT reconstructionen_AU
dc.subjectsource deblurringen_AU
dc.subjecthigh-cone angle CTen_AU
dc.subjectphase contrasten_AU
dc.subjectphase retrievalen_AU
dc.subjectlinear iterative multi-energy methoden_AU
dc.subjectspace filling trajectoryen_AU
dc.titlePartially Coherent Lab Based X-ray Micro Computed Tomographyen_AU
dc.typeThesis (PhD)en_AU
dcterms.valid2017en_AU
local.contributor.affiliationDepartment of Applied Mathematics, College of Physical & Mathematical Sciences, The Australian National Universityen_AU
local.contributor.authoremailheyang.li.nz@gmail.comen_AU
local.contributor.supervisorSheppard, Adrian
local.contributor.supervisorcontactadrian.sheppard@anu.edu.auen_AU
local.description.notesThe author deposited 1/05/17en_AU
local.identifier.doi10.25911/5d74e230f2ca8
local.mintdoimint
local.type.degreeDoctor of Philosophy (PhD)en_AU

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