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首页> 外文会议>Physics of Medical Imaging pt.3; Progress in Biomedical Optics and Imaging; vol.7 no.28 >Elliptical Extrapolation of Truncated 2D CT Projections Using Helgason-Ludwig Consistency Conditions
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Elliptical Extrapolation of Truncated 2D CT Projections Using Helgason-Ludwig Consistency Conditions

机译：使用Helgason-Ludwig一致性条件的截断二维CT投影的椭圆外推

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摘要

Image reconstruction from truncated tomographic data is an important practical problem in CT in order to reduce the X-ray dose and to improve the resolution. The main problem with the Radon Transform is that in 2D the inversion formula globally depends upon line integrals of the object function. The standard Filtered Backprojection algorithm (FBP) does not allow any type of truncation. A typical strategy is to extrapolate the truncated projections with a smooth 1D function in order to reduce the discontinuity artefacts. The low-frequency artifact reduction however, severely depends upon the width of the extrapolation, which is unknown in practice. In this paper we develop a modified ConTraSPECT-type method for specific use on truncated 2D CT-data, when only a local area (ROI) is to be imaged. The algorithm describes the shape and structure of the region surrounding the ROI by a specific object with only few parameters, in this paper a uniform ellipse. The parameters of this ellipse are optimized by minimizing the Helgason-Ludwig consistency conditions for the sinogram completed with Radon data of the ellipse. Simulations show that the MSE of the reconstructions is reduced significantly, depending on the type of truncation.
机译：从断层断层摄影数据重建图像是CT中一个重要的实际问题，以减少X射线剂量并提高分辨率。 Radon变换的主要问题是在2D中，反演公式总体上取决于对象函数的线积分。标准的过滤反投影算法（FBP）不允许任何类型的截断。一种典型的策略是用平滑的一维函数外推截断的投影，以减少不连续性伪影。然而，低频伪像的减少严重取决于外推的宽度，这在实践中是未知的。在本文中，我们开发了一种改进的ConTraSPECT类型的方法，专门用于仅对局部区域（ROI）成像的2D截断CT数据。该算法通过仅具有少量参数的特定对象（在本文中是均匀的椭圆）来描述ROI周围区域的形状和结构。通过最小化用椭圆的Radon数据完成的正弦图的Helgason-Ludwig一致性条件，可以优化此椭圆的参数。仿真表明，根据截断的类型，重构的MSE显着降低。

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