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Comparison Between Projection Weighting and Rebinning Approaches in Analytical Image Reconstruction in Off-Center Flat Panel Cone-Beam CT Imaging

机译:偏心平板锥束CT成像分析图像重建中投影加权和重组方法的比较

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In cone-beam CT (CBCT) imaging, a half-fan (HF) mode acquisition can be used to obtain a larger field-of-view (FOV) without physically increasing the detector size. However, this leads to an asymmetric sinogram with a truncated set of projection that needs to be considered during image reconstruction., especially when using analytical methods such as the filtered backprojection (FBP) and its 3D approximation, the Feldkamp-Davis-Kress (FDK) algorithm. Various approaches have been suggested in literature, which can be roughly categorized as weighting based and projection rebinning approaches. In this paper, a comparison between the two approaches are made using the XCAT phantom, based on the geometry of the Varian On-Board Imager (OBI) as the CBCT acquisition device that is usually used for image guided radiotherapy (IGRT) during treatment delivery. It is found that analytical reconstruction alone will produce a percent normalized root mean squared error (NRMSE) of 36.81% in the reconstructed image, whereas using the weighting based and rebinning approaches reduces this error to 22.86% and 4.68% respectively. Apart from that, the weighting based approach is also found to be on average biased and produces an overall lower intensity in the reconstructed image whereas the rebinning approach does not have this problem, as well as having a smaller standard deviation of the intensity deviations from the original phantom image as the ground truth.
机译:在锥束CT(CBCT)成像中,可以使用半扇(HF)模式采集来获得更大的视场(FOV),而无需实际增加检测器的尺寸。但是,这会导致在投影图像重建期间需要考虑到投影被截断的不对称正弦图,特别是在使用诸如滤波反投影(FBP)及其3D近似分析方法,Feldkamp-Davis-Kress(FDK)等分析方法时)算法。文献中已经提出了各种方法,这些方法可以粗略地分类为基于加权的方法和投影重组方法。在本文中,基于Varian车载成像器(OBI)作为CBCT采集设备的几何结构,使用XCAT幻象对两种方法进行了比较,该CBCT采集设备通常在治疗过程中用于图像引导放射治疗(IGRT) 。发现仅解析重建将在重建图像中产生36.81%的归一化均方根误差(NRMSE)百分比,而使用基于权重和重新组合的方法分别将该误差降低到22.86%和4.68%。除此之外,还发现基于加权的方法平均偏向,并在重建图像中产生总体较低的强度,而重新合并方法则不存在此问题,并且强度偏离标准值的标准偏差较小。原始的幻像作为地面真理。

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