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ABSTRACT: A multiple-slit collimator (MSC) design was introduced for scatter reduction in cone-beam computed tomography (CBCT). Unlike most other collimators, the open and closed septa of the proposed MSC are placed in an equi-angular interval on a circular track of the central sagittal plane. Therefore, one gantry rotation provides only the half of necessary dataset and two gantry rotations are needed to obtain full information. During the first gantry rotation, the MSC position relative to the source is fixed. For the second rotation, the MSC is rotated by the equi-angle interval. We assume signals under the closed septa are totally attributed to scatter radiation. Then, scatter contributions under open septa are determined by interpolating them.Monte Carlo (MC) simulations for two virtual phantoms (one with a simple geometry and the other with two heterogeneities simulating the bone and the lung) were performed to evaluate the effectiveness of the system. Using the method developed, we could obtain images with significant scatter reduction. Contrast ratio (CR) improvement factors were 1.165 in a 2D projection view, and 1.210 and 1.223 at the central and peripheral slice of the reconstructed CBCT image of the simple geometry phantom.This preliminary study demonstrated that the proposed MSC, together with the imaging process technique, had a great potential to reduce scatter contribution in CBCT. Further studies will be performed to investigate the effect of various factors, such as reducing the detector size, increasing the number of history of MC simulation, and including many structures with different densities.
Journal of Applied Clinical Medical Physics 01/2010; 11(4):3269. · 0.96 Impact Factor
Journal- Korean Physical Society 07/2008; 53:863. · 0.51 Impact Factor
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ABSTRACT: Anti-scatter grids show various performances depending on the complicated design parameters. However, it takes long time and cost to fabricate grids and perform experiments to evaluate the performance of grids. Therefore, to replace actual measurements, we performed Monte Carlo simulation study and obtained Tp (transmission of primary radiation) and Tt (transmission of total radiation) values which represent grid performance. Beam quality check was done to validate our simulation results. Although the simulation lowers the cost, it is still time consuming work. To solve those problems, empirical formulae for Tp and Tt were derived by analyzing the results of the simulation. Design parameters for grids were setup in order to derive the empirical formulae. The derived empirical formulae helped us estimate Tp and Tt values of an arbitrary grid without a complicated experiment or a tedious simulation, and easily obtain contrast improvement factor (CIF) and Bucky factor (BF) which are commonly used to evaluate the performance of a grid. The design parameters of a grid for the minimum patient's dose can be proposed with maintaining the image quality within the designable range using the derived empirical formulae.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE; 01/2008