A Study of Monochromatic X-ray Area Beam for Application in Diffraction Enhanced Imaging

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Title: A Study of Monochromatic X-ray Area Beam for Application in Diffraction Enhanced Imaging
Author: Kim, Chang Hyeuk
Advisors: Mohamed A. Bourham, Committee Chair
Man-Sung Yim, Committee Member
J. Michael Doster, Committee Member
David S. Lalush, Committee Member
Abstract: Synchrotron-based Diffraction Enhanced Imaging (DEI) system has shown improved contrast images on low attenuation material. In a previous DEI study great potential to detect earlier stage breast cancer was reported. However, to apply DEI technique at the clinical level, a synchrotron source is not feasible for clinically-approved systems due to the size of the accelerator, and hence a compact x-ray source that can replace synchrotron is desirable. Development of an x-ray source compatible to synchrotron radiation is an essential part for a clinical DEI system. Some important features for the design of an x-ray source, based on synchrotron radiation, are the photon flux and beam collimation. The NCSU research group suggested a wide-beam x-ray source, which consists of concentric circular filaments producing electron flux onto a cylindrically-shaped oxygen-free copper stationary target with a thin layer of Molybdenum for x-ray production. This source design emphasizes large field of view, which can eliminate the line by line scanning process experienced in a DEI experimental setup. In this study, the proof of principle model of a wide beam x-ray source was used to study for control electron trajectory of the concentric filaments design, calculations of the produced x-ray flux, simulation of the DEI imaging, and estimation of the operation time with target's active cooling system. The DEI images from the electron distribution were computationally generated by adopting a monochromator and an analyzer with a computationally generated dual cylindrical object. The image simulation showed that the wide-beam x-ray source based DEI images are highly dependent on the electron distribution at the target. Uniform electron distribution by electron trajectory optimization is carried out through independent powering of the filaments inside the focusing cup. For higher electron beam current the x-ray flux satisfies obtaining a successful DEI image scan, but such high current increases the heat loading on the target. The target cooling with a contact cold finger does not provide sufficient thermal management, and hence not enough scanning time. The impinging jet nozzle cooling option was investigated to maximize convective heat transfer, and has shown feasible thermal management and adequate operation time for DEI imaging.
Date: 2008-08-21
Degree: PhD
Discipline: Nuclear Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/4276

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