Advanced single-slice rebinning in cone-beam spiral CT: theoretical considerations and medical applications
Advanced single-slice rebinning in cone-beam spiral CT: theoretical considerations and medical applications
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锥束螺旋 CT 中的高级单层重组：理论考虑和医学应用
DOI：
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发表时间：
2000
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通讯作者：
W. Kalender
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文献类型：
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作者：
M. Kachelriess;S. Schaller;W. Kalender
为了在计算机断层扫描 (CT) 中以改进的 z 分辨率实现更高的体积覆盖范围，需要具有大量探测器行的系统。然而，与当今的四切片扫描仪相比，处理更多数量的探测器行需要考虑光束的锥形几何形状。在过去的十年中，已经提出了许多所谓的锥束重建算法。没有一种能够满足医用螺旋锥束CT对高图像质量、低患者剂量和低重建时间的所有要求。因此，我们提出了一种近似锥束算法，该算法使用倾斜的虚拟重建平面来最佳地拟合 180 度螺旋段，即先进的单切片重组（ASSR）算法。我们的算法是 Noo 等人提出的单切片重组算法的修改版。 [物理。医学。生物。 44, 561-570 (1999)]因为我们使用倾斜重建切片而不是横轴切片来近似螺旋路径。进行了理论考虑以及与金标准 180 度 LI（单层螺旋 CT）相比的模拟体模数据的重建。对所有模拟扫描仪的图像伪影、z 分辨率以及噪声水平进行了评估。即使对于大量探测器行，重建图像中的伪影水平仍然与 180 度 LI 的水平相当。 Defrise 体模的多平面重构显示，在锥角较大时通常会出现典型的锥束伪影。图像噪声以及各个切片灵敏度分布的形状相当于单切片螺旋重建，z 分辨率略有下降。 ASSR 有潜力成为医用螺旋锥束 CT 的实用工具。其计算复杂度相当于标准单层 CT 的数量级，并且允许使用可用的 2D 反投影硬件。
To achieve higher volume coverage at improved z-resolution in computed tomography (CT), systems with a large number of detector rows are demanded. However, handling an increased number of detector rows, as compared to today's four-slice scanners, requires to accounting for the cone geometry of the beams. Many so-called cone-beam reconstruction algorithms have been proposed during the last decade. None met all the requirements of the medical spiral cone-beam CT in regard to the need for high image quality, low patient dose and low reconstruction times. We therefore propose an approximate cone-beam algorithm which uses virtual reconstruction planes tilted to optimally fit 180 degrees spiral segments, i.e., the advanced single-slice rebinning (ASSR) algorithm. Our algorithm is a modification of the single-slice rebinning algorithm proposed by Noo et al. [Phys. Med. Biol. 44, 561-570 (1999)] since we use tilted reconstruction slices instead of transaxial slices to approximate the spiral path. Theoretical considerations as well as the reconstruction of simulated phantom data in comparison to the gold standard 180 degrees LI (single-slice spiral CT) were carried out. Image artifacts, z-resolution as well as noise levels were evaluated for all simulated scanners. Even for a high number of detector rows the artifact level in the reconstructed images remains comparable to that of 180 degrees LI. Multiplanar reformations of the Defrise phantom show none of the typical cone-beam artifacts usually appearing when going to larger cone angles. Image noise as well as the shape of the respective slice sensitivity profiles are equivalent to the single-slice spiral reconstruction, z-resolution is slightly decreased. The ASSR has the potential to become a practical tool for medical spiral cone-beam CT. Its computational complexity lies in the order of standard single-slice CT and it allows to use available 2D backprojection hardware.