Browsing by Author "Liu, Xiaokang"
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Item Demonstration and optimization of X-ray StaticCodeCT(University of Delaware, 2022) Liu, XiaokangSince Sir Godfrey Hounsfield invented the first CT scanner in 1967, the practice of X-ray computed tomography (CT) has exploded. X-ray CT has become widely employed in medical diagnosis in the last half-century. As more information about X-ray radiation becomes available, so does concern about the potential for radiation exposure to cause cancer. To alleviate some of this problem, state-of-the-art techniques have focused on hardware design constraints and reconstruction algorithm development. To block the radiation, coded aperture X-ray imaging, for example, inserts coded aperture masks in front of the X-ray source at each view angle. The image is then reconstructed by solving a l1-based optimization problem, due to the inverse problem's ill-posedness. Unfortunately, with this approach, the best reconstructions are obtained when distinct masks are employed in each view angle, which makes it impractical in real-world applications. In this thesis, a single-static coded aperture is used in StaticCodeCT, a newly developed low-dose tomography design. It utilizes data with high correlation in the projection range and algorithms developed to accurately approximate the detector's missing measurements across the spatial and axial dimensions. Using iterative image reconstruction or so called the FDK algorithm, the object from a complete set of cone-beam synthesized projections is successfully recovered. The effect of StaticCodeCT system was investigated before by simulating the coded aperture mask on CT data from experiments. A preliminary cone-beam X-ray CT system with a coded aperture holder is used in this study to offer test bench reconstructions. We looked at the quality of the reconstruction by using coded apertures made with two different techniques: metal additive manufacturing and cold-cast manufacturing with plastic mold. Additionally, based on the measurement estimation methodology, we offer an optimization strategy for designing the coded aperture pattern. The observed results suggest that real-world deployment of StaticCodeCT systems is possible.Item Experimental demonstration and optimization of X-ray StaticCodeCT(Applied Optics, 2021-10-18) Cuadros, Angela P.; Liu, Xiaokang; Parsons, Paul E.; Ma, Xu; Arce, Gonzalo R.As the use of X-ray computed tomography (CT) grows in medical diagnosis, so does the concern for the harm a radiation dose can cause and the biological risks it represents. StaticCodeCT is a new low-dose imaging architecture that uses a single-static coded aperture (CA) in a CT gantry. It exploits the highly correlated data in the projection domain to estimate the unobserved measurements on the detector. We previously analyzed the StaticCodeCT system by emulating the effect of the coded mask on experimental CT data. In contrast, this manuscript presents test-bed reconstructions using an experimental cone-beam X-ray CT system with a CA holder. We analyzed the reconstruction quality using three different techniques to manufacture the CAs: metal additive manufacturing, cold casting, and ceramic additive manufacturing. Furthermore, we propose an optimization method to design the CA pattern based on the algorithm developed for the measurement estimation. The obtained results point to the possibility of the real deployment of StaticCodeCT systems in practice.Item X-ray Compton backscattering imaging via structured light(Optics Express, 2022-04-20) Salazar, Edgar; Liu, Xiaokang; Arce, GonzaloCompton backscattering imaging (CBI) is a technique that uses ionizing radiation to detect the presence of low atomic number materials on a given target. Unlike transmission x-ray imaging, the source and sensor are located on the same side, such that the photons of interest are scattered back after the radiation impinges on the body. Rather than scanning the target pixel by pixel with a pencil-beam, this paper proposes the use of cone-beam coded illumination to create the compressive x-ray Compton backscattering imager (CXBI). The concept was developed and tested using Montecarlo simulations through the Geant4 application for tomography emissions (GATE), with conditions close to the ones encountered in experiments, and posteriorly, a test-bed implementation was mounted in the laboratory. The CXBI was evaluated under several conditions and with different materials as target. Reconstructions were run using denoising-prior-based inverse problem algorithms. Finally, a preliminary dose analysis was done to evaluate the viability of CXBI for human scanning.