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Title: Annular beam X-ray imaging
Author: Godber, S. X.
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2014
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This thesis presents an investigation of depth‐resolved absorption imaging by scanning objects through an annular beam of X‐rays. The resultant ring shaped projections record depth dependent parallax. The study focuses on two different scanning methods. First, a single axis scan has been employed to record curvilinear stereoscopic images. Second, a two axis raster scanning approach enables focal plane images to be produced via tomosynthesis. These novel absorption contrast methods have been carefully designed to complement X-ray diffraction considerations. Prior work employing an annular beam concerned the collection of X­ray diffraction data for structural analysis/phase identification. This method, termed Focal Construct Geometry (FCG), provided orders of magnitude increase in the intensity of the diffracted X-rays within the beam’s dark interior to enable rapid processing. However, this work relied upon a priori sample position. The research presented in this thesis establishes a complementary absorption imaging modality, which is designed to support and inform the analysis of the diffraction data by providing quantitative spatial information. This approach is essential for the autonomous interrogation of unknown objects at unknown positions within an inspection volume e.g. aviation security baggage screening. Two novel approaches have been developed and investigated. The first, termed Annular Beam Scanning (ABS), treats each annular field as a pair of semi‐annular projections as defined by an axis perpendicular to the scan direction. The resultant curvilinear stereoscopic image pairs contain depth dependent parallax along this scan direction. Algorithms to extract three‐dimensional information from the curvilinear images have been derived and validated. It has been shown that range information is proportional to the opening half‐angle ϕ of the annular beam but inversely proportional to the angular position σ of each matched element pair on the semi‐annular sensors. The second approach reassembles pixel data from a matrix of annular projections to form Multidirectional Perspective Views (MPV). These views encode object range as circular parallax. The application of Digital Tomosynthesis (DTS) employing a Shift‐and‐Add process enables focal plane images to be recorded. Unlike conventional DTS the minimum resolvable axial increment is independent of focal plane position within the inspected volume. While both approaches provide three‐dimensional data, MPV/DTS is the optimal method for combination with FCG diffraction datasets. The final part of this thesis describes results combining DTS with simulated diffraction image spaces to autonomously determine 2θ diffraction angles. This research programme has established a new annular beam imaging modality, which contributes significantly to the body of knowledge in the field of analytical 3D X‐ray imaging.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available