Date of Award

1-1-2022

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Physics

Content Description

1 online resource (vi, 114 pages) : illustrations (some color)

Dissertation/Thesis Chair

Carolyn A. MacDonald

Committee Members

Hassan Abbas, Ariel Caticha, Alexander Khmaladze

Keywords

Radiography, Diagnostic imaging, Gamma rays

Subject Categories

Radiology

Abstract

Imaging can be performed with a variety of techniques. For example, gamma radiation is used in nuclear medicine and radiation therapy A challenge in using gamma rays is the risk of high radiation exposure, which requires extensive custom shielding. The transmission of gamma rays through 3D printed shielding was measured to evaluate the required thickness of the shielding.Conventional radiography depends on x-ray attenuation. Another imaging technique, X-ray phase imaging, is known to improve the contrast of images relative to conventional imaging for low density materials. Phase differences imparted by soft tissue are roughly 1000 times larger than attenuation differences. Further, because phase imaging depends on the real part of the index of refraction of tissues, true phase images might be employed for tissue typing. Complementary information can be obtained simultaneously from small angle scattering off of tissue microstructure, which can provide an additional “dark field” signal. While quantitative phase can provide some tissue typing information, additional structure can be revealed by incorporating the dark field images. Dark field images have received attention for the potential application in lung disease, differentiation of kidney stones and identification of masses and microcalcifications in mammography. The acquisition of phase and dark field images typically requires highly coherent illumination, such as synchrotrons, low power micro focus sources or multiple precisely machined and aligned gratings, which may limit the clinical applicability of these techniques. Our method employs a single, low-cost wire mesh that does not need precise alignment and relaxes the coherence requirement on the source. Further coherence requirement reduction is provided with focusing polycapillary optics. The system has been employed to produce high contrast absorption images with simultaneous differential phase contrast images and dark field images. Resolution was enhanced with a mesh-shifting algorithm and source and camera deconvolution. However, the coarseness of the mesh reduces the strength of the phase and dark field signal compared with grating-based techniques, so it is important to design a system to optimize signal to noise ratio. We performed optimization experiments by adjusting distances between the source, mesh, phantom and detector, and varying the x-ray energy. We also studied the beam hardening artifacts on mesh-based system. Mesh-based phase imaging is a promising technique for including phase and dark field imaging into a clinical setup. It is an important to develop mesh-based computed tomography and tomosynthesis, to build up three-dimensional information, as this is the current best practice in mammography. We developed the mesh-based phase and dark field imaging computed tomography system. Furthermore, coherent scatter imaging with the polycapillary optics was done to study the possibility of incorporating it to the mesh-based phase imaging setup which could provide the simultaneous attenuation, phase, dark field and coherent scatter information.

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