Coded Aperture X-ray Tomographic Imaging with Energy Sensitive Detectors
Coherent scatter imaging techniques have experienced a renaissance in the past two decades from an evolution of detector technology and computational imaging techniques. X-ray diffraction requires a precise knowledge of object location and is time consuming; transforming diffractometry into a practical imaging technique involves spatially resolving the sample in 3-dimensions and speeding up the measurement process. The introduction of a coded aperture in a conventional X-ray diffraction system provides 3D localization of the scatterer as well as drastic reductions in the acquisition time due to the ability to perform multiplexed measurements. This theses document contains two strategies involving coded apertures to address the aforementioned challenges of X-ray coherent scatter measurements.
The first technique places the coded aperture between source and object to structure the incident illumination. A single pixel detector captures temporally modulated coherent scatter data from an object as it travels through the illumination. From these measurements, 2D spatial and 1D spectral information is recovered at each point within a planar slice of an object. Compared to previous techniques, this approach is able to reduce the overall scan time of objects by 1-2 orders of magnitude.
The second measurement technique demonstrates snapshot coherent scatter tomography. A planar slice of an object is illuminated by a fan beam and the scatter data is modulated by a coded aperture between object and detector. The spatially modulated data is captured with a linear array of energy sensitive detectors, and the recovered data shows that the system can image objects that are 13 mm in range and 2 mm in cross range with a fractional momentum transfer resolution of 15\%. The technique also allows a 100x speedup when compared to pencil beam systems using the same components.
Continuing with the theme of snapshot tomography with energy sensitive detectors, I study the impact of detectors properties such as detection area, choice of energies and energy resolution for pencil and fan beam coded aperture coherent scatter systems. I simulate various detector geometries and determine that energy resolution has the largest impact for pencil beam geometries while detector area has the largest impact for fan beam geometries. These results can be used to build detectors which can potentially help implement pencil and/or fan beam coded aperture coherent scatter systems in applications involving medicine and security.
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