نتایج جستجو برای: focus fan beam collimator
تعداد نتایج: 468240 فیلتر نتایج به سال:
This thesis addresses the problem of reconstructing static objects in 2D and 3D transmission computed tomography (CT). After reviewing the classical CT reconstruction theory, we discuss and thoroughly evaluate various novel reconstruction methods, two of which are original. Our first original approach is for 2D CT reconstruction from full-scan fan-beam data, i.e., for 2D imaging in the geometry...
In this paper, we consider tomographic reconstruction for axially symmetric objects from a single radiograph formed by fan-beam X-rays. All contemporary methods are based on the assumption that the density is piecewise constant or linear. From a practical viewpoint, this is quite a restrictive approximation. The method we propose is based on high-order total variation regularization. Its main a...
Existing algorithms for exact helical cone beam (HCB) tomographic reconstruction are computationally infeasible for clinical applications. Their computational cost is dominated by 3-D backprojection, which is generally an operation. We present a fast hierarchical 3-D backprojection algorithm, generalizing fast 2-D parallel beam and fan beam algorithms, which reduces the overall complexity of th...
New fan-beam DXA systems can detect vertebral fractures with fast, low-dose lateral scans of the vertebra from T4 to L4 in as little as 10 seconds. Vertebral fractures are the most common fracture in osteoporosis and an indication for treatment irrespective of Bone Mineral Density [1-3]. However, without a diagnostic test such as that available on fan-beam DXA systems, as many as 75% of vertebr...
We propose two algorithms for the reconstruction of a 2D object from its continuous projections. The first algorithm operates on parallel projection data, while the second uses the more practical model of fan-beam projections. Both algorithms are based on the discrete Radon transform, which extends the continuous Radon transform to discrete data. The discrete Radon transform and its inverse can...
Electron beam welding has shown a remarkable job in the space industry for welding of components. It is performed under a vacuum environment that eliminates foreign matter such as hydrogen, oxygen, and other gases. Joining of similar and dissimilar materials is the main advantage of electron beam welding with high depth to width ratio as well as sharp focus at the point where parts are to be we...
Purpose: Compton spectroscopy is a widely accepted tool for measuring the primary X-ray spectra of a diagnostic computed tomography (CT) system. The aim of this work is to spectroscopically detect CT X-ray photons subjected to 90-degree Compton scattering for accurate modelling of CT beam-shaping filtration, which necessary for computation of radiation exposure and for other research applicatio...
We explore the influence of local strain on the electronic structure of graphene. We show that strain can be easily tailored to generate electron beam collimation, 1D channels, surface states, and confinement. These can be seen as basic elements for all-graphene electronics which, by suitable engineering of local strain profiles, could be integrated on a single graphene sheet. In addition this ...
The volume reflection phenomenon was detected while investigating 400 GeV proton interactions with bent silicon crystals in the external beam H8 of the CERN Super Proton Synchrotron. Such a process was observed for a wide interval of crystal orientations relative to the beam axis, and its efficiency exceeds 95%, thereby surpassing any previously observed value. These observations suggest new pe...
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