X-ray scatter tomography using coded apertures Public Deposited

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  • March 20, 2019
Creator
  • MacCabe, Kenneth
    • Affiliation: College of Arts and Sciences, Department of Physics and Astronomy
Abstract
  • This work proposes and studies a new field of x-ray tomography which combines the principles of scatter imaging and coded apertures, termed coded aperture x-ray scatter imaging (CAXSI). Conventional x-ray tomography reconstructs an object's electron density distribution by measuring a set of line integrals known as the x-ray transform, based physically on the attenuation of incident rays. More recently, scatter imaging has emerged as an alternative to attenuation imaging by measuring radiation from coherent and incoherent scattering. The information-rich scatter signal may be used to infer density as well as molecular structure throughout a volume. Some scatter modalities use collimators at the source and detector, resulting in long scan times due to the low efficiency of scattering mechanisms combined with a high degree of spatial filtering. CAXSI comes to the rescue by employing coded apertures. Coded apertures transmit a larger fraction of the scattered rays than collimators while also imposing structure to the scatter signal. In a coded aperture system each detector is sensitive to multiple ray paths, producing multiplexed measurements. The coding problem is then to design an aperture which enables de-multiplexing to reconstruct the desired physical properties and spatial distribution of the target. In this work, a number of CAXSI systems are proposed, analyzed, and demonstrated. One-dimensional pencil beams, two-dimensional fan beams, and three-dimensional cone beams are considered for the illumination. Pencil beam and fan beam CAXSI systems are demonstrated experimentally. The utility of energy-integrating (scintillation) detectors and energy-sensitive (photon counting) detectors are evaluated theoretically, and new coded aperture designs are presented for each beam geometry. Physical models are developed for each coded aperture system, from which resolution metrics are derived. Systems employing different combinations of beam geometry, coded apertures, and detectors are analyzed by constructing linear measurement operators and comparing their singular value decompositions. Since x-ray measurements are typically dominated by photon shot noise, iterative algorithms based on Poisson statistics are used to perform the reconstructions. This dissertation includes previously published and unpublished co-authored material.
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  • In Copyright
Advisor
  • Zhou, Otto
Degree
  • Doctor of Philosophy
Graduation year
  • 2014
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