Exact reconstruction of volumetric images in reverse helical cone-beam CT
Exact reconstruction of volumetric images in reverse helical cone-beam CT
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DOI：
10.1118/1.2936219
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发表时间：
2008-07-01
期刊：
影响因子：
3.8
通讯作者：
Pan, Xiaochuan
中科院分区：
文献类型：
--
作者：
Cho, Seungryong;Xia, Dan;Pan, Xiaochuan
螺旋扫描配置已广泛用于诊断锥束计算机断层扫描 (CBCT)，用于获取足以在扩展体积上进行精确图像重建的数据。在图像引导放射治疗 (IGRT) 和 CBCT 的其他应用中，由于硬件限制，在成像系统上机械地实现多圈螺旋轨迹即使不是不可能，也可能很困难。然而，这些应用中的成像系统通常允许实现反向螺旋轨迹，其中旋转方向在连续两圈之间改变。由于反向螺旋轨迹满足 Tuy 条件，因此当成像对象的投影未被截断时，它会产生足以在反向螺旋体积内进行精确图像重建的数据。最近开发的基于弦的算法，例如反投影过滤（BPF）算法，可以很容易地应用于重建反向螺旋轨迹的弦上的图像，因此它们可以重建被弦覆盖的体积内的图像。相反，基于弦的算法无法重建未与弦相交的区域内的图像。在反向螺旋体积中，如下所示，存在无弦区域，因此在其中不能使用基于弦的算法来重建图像。在这项工作中，基于 Pack-Noo 公式，推导了一种平移不变滤波反投影 (FBP) 算法，用于反向螺旋体积（包括无弦区域）内的精确图像重建。还进行了数值研究来演示反向螺旋体积中的无弦区域，并验证用于无弦区域内图像重建的 FBP 算法。数值研究的结果证实，FBP 算法可以准确地重建整个反向螺旋体积内的图像，包括无弦区域。扩展 FBP 算法来重建一般轨迹的图像相对简单，包括具有可变螺距、倾斜轴和/或转弯之间的附加段的反向螺旋轨迹。 (C) 2008 年美国医学物理学家协会。
Helical scanning configuration has been used widely in diagnostic cone-beam computed tomography (CBCT) for acquiring data sufficient for exact image reconstruction over an extended volume. In image-guided radiation therapy (IGRT) and other applications of CBCT, it can be difficult, if not impossible, to implement mechanically a multiple-turn helical trajectory on the imaging systems due to hardware constraints. However, imaging systems in these applications often allow for the implementation of a reverse helical trajectory in which the rotation direction changes between two consecutive turns. Because the reverse helical trajectory satisfies Tuy's condition, when projections of the imaged object are nontruncated, it yields data sufficient for exact image reconstruction within the reverse helix volume. The recently developed chord-based algorithms such as the backprojection filtration (BPF) algorithm can readily be applied to reconstructing images on chords of a reverse helical trajectory, and they can thus reconstruct an image within a volume covered by the chords. Conversely, the chord-based algorithms cannot reconstruct images within regions that are not intersected by chords. In a reverse helix volume, as shown below, chordless regions exist in which no images can thus be reconstructed by use of the chord-based algorithms. In this work, based upon Pack-Noo's formula, a shift-invariant filtered backprojection (FBP) algorithm is derived for exact image reconstruction within the reverse helix volume, including the chordless region. Numerical studies have also been conducted to demonstrate the chordless region in a reverse helix volume and to validate the FBP algorithm for image reconstruction within the chordless region. Results of the numerical studies confirm that the FBP algorithm can exactly reconstruct an image within the entire reverse helix volume, including the chordless region. It is relatively straightforward to extend the FBP algorithm to reconstruct images for general trajectories, including reverse helical trajectories with variable pitch, tilted axis, and/or additional segments between turns. (C) 2008 American Association of Physicists in Medicine.