A local shift-variant Fourier model and experimental validation of circular cone-beam computed tomography artifacts
A local shift-variant Fourier model and experimental validation of circular cone-beam computed tomography artifacts
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DOI：
10.1118/1.3062875
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发表时间：
2009-02-01
期刊：
影响因子：
3.8
通讯作者：
Jaffray, David
中科院分区：
文献类型：
--
作者：
Bartolac, Steven;Clackdoyle, Rolf;Jaffray, David
大视场锥束计算机断层扫描（CBCT）是实现使用圆形源和探测器轨迹。众所周知，这些圆形轨迹收集的数据不足以进行准确的图像重建。虽然存在各种对缺失信息的描述，但这种数据缺失在重建图像中的表现通常是不直观的。一个模型预测，缺失的信息对应于缺失频率分量的移位变锥。这种描述意味着伪影依赖于成像几何形状，以及成像对象的频率内容。特别是，能量分布在与丢失的锥体重合的频带上的大比例物体将受到最大的损害。通过在物体空间的不同位置成像小的局部物体（丙烯酸球，堆叠磁盘）并观察重建的频谱，这些预测得到了实验验证。对丢失的圆锥体的内角的测量与理论非常吻合，表明在旋转轴上的点是一个右圆锥体，在其他地方是一个斜圆锥体。在前一种情况下，相对于垂直轴的最大内角对应于CBCT系统的（半）锥角（通常类似于IGRT的5度-7.5度）。正如预期的那样，物体的恢复也强烈依赖于物体的频谱相对于丢失的锥体的分布。通过去除局部频率成分，观察到的伪影也可重现，进一步支持理论模型。与之前的结果相比，具有不同内部结构（蜂窝聚氨酯，固体丙烯酸）的较大物体也进行了成像和解释。最后，使用临床CBCT扫描仪获得的小动物数据被观察到锥体缺失的证据。本研究深入探讨了数据收集不完整对大视场CBCT成像对象外观的影响。
Large field of view cone-beam computed tomography (CBCT) is being achieved using circular source and detector trajectories. These circular trajectories are known to collect insufficient data for accurate image reconstruction. Although various descriptions of the missing information exist, the manifestation of this lack of data in reconstructed images is generally nonintuitive. One model predicts that the missing information corresponds to a shift-variant cone of missing frequency components. This description implies that artifacts depend on the imaging geometry, as well as the frequency content of the imaged object. In particular, objects with a large proportion of energy distributed over frequency bands that coincide with the missing cone will be most compromised. These predictions were experimentally verified by imaging small, localized objects (acrylic spheres, stacked disks) at varying positions in the object space and observing the frequency spectrums of the reconstructions. Measurements of the internal angle of the missing cone agreed well with theory, indicating a right circular cone for points on the rotation axis, and an oblique, circular cone elsewhere. In the former case, the largest internal angle with respect to the vertical axis corresponds to the (half) cone angle of the CBCT system (typically similar to 5 degrees-7.5 degrees in IGRT). Object recovery was also found to be strongly dependent on the distribution of the object's frequency spectrum relative to the missing cone, as expected. The observed artifacts were also reproducible via removal of local frequency components, further supporting the theoretical model. Larger objects with differing internal structures (cellular polyurethane, solid acrylic) were also imaged and interpreted with respect to the previous results. Finally, small animal data obtained using a clinical CBCT scanner were observed for evidence of the missing cone. This study provides insight into the influence of incomplete data collection on the appearance of objects imaged in large field of view CBCT.