Browsing by Author "Meaney, Alexander"

X-ray computed tomography (CT) is widely used in medical imaging and materials science. In this imaging modality, cross-sectional images of a physical object are formed by taking numerous X-ray projections from different angles and then applying a reconstruction algorithm to the measured data. The cross-sectional slices can be used to form a three-dimensional model of the interior structure of the object. CT is a prime example of an inverse problem, in which the aim is to recover an unknown cause from a known effect. CT technology continues to develop, motivated by the desire for increased image quality and spatial resolution in reconstructions. In medical CT, reducing patient dose is a major goal. The branch of CT known as X-ray microtomography (micro-CT) produces reconstructions with spatial resolutions in the micrometer range. Micro-CT has been practiced at the University of Helsinki since 2008. The research projects are often interdisciplinary, combining physics with fields such as biosciences, paleontology, geology, geophysics, metallurgy and food technology. This thesis documents the design and construction of a new X-ray imaging system for computed tomography. The system is a cone beam micro-CT scanner intended for teaching and research in inverse problems and X-ray physics. The scanner consists of a molybdenum target X-ray tube, a sample manipulator, and a flat panel detector, and it is built inside a radiation shielding cabinet. Measurements were made for calibrating the measurement geometry and for testing reconstruction quality. Two-dimensional reconstructions of various samples were computed using the plane which passes through the X-ray point source and is perpendicular to the axis of rotation. This central plane of the cone beam reduces to fan beam geometry. All reconstructions were computed using the filtered backprojection (FBP) algorithm, which is the industry standard. Tomographic reconstructions of high quality were obtained from the measurements. The results show that the imaging system is well suited for CT and the study of reconstruction algorithms.