Algorithm for X-ray Scatter, Beam-Hardening, and Beam Profile Correction in Diagnostic (Kilovoltage) and Treatment (Megavoltage) Cone Beam CT
Algorithm for X-ray Scatter, Beam-Hardening, and Beam Profile Correction in Diagnostic (Kilovoltage) and Treatment (Megavoltage) Cone Beam CT
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DOI：
10.1109/tmi.2008.928922
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发表时间：
2008-12-01
影响因子：
10.6
通讯作者：
Bani-Hashemi, Ali R.
中科院分区：
文献类型：
--
作者：
Maltz, Jonathan S.;Gangadharan, Bijumon;Bani-Hashemi, Ali R.
锥形束x射线计算机断层扫描（CT）数据集的定量重建需要精确的散射、波束硬化、波束剖面和探测器响应建模。通常，商业成像系统使用快速经验校正，旨在减少由于图像形成过程建模不完整而导致的可见伪影。相比之下，蒙特卡罗（MC）方法更准确，但速度相对较慢。散射核叠加（SKS）方法在精度和计算实用性之间取得了平衡。我们展示了如何使用单个SKS算法来校正千伏（kV）能量（诊断）和兆伏（MV）能量（治疗）x射线图像。利用kV和MV成像系统的MC模型，我们将在非晶硅平板探测器上记录的强度映射到水当量厚度（WETs）。散点图是利用局部WET值索引的散点核从获得的投影图像中导出的，然后使用散点幅度边界方案进行迭代细化，该方案允许算法适应kV成像中遇到的非常高的散点与原初比。该算法在千伏和兆伏特能量下将辐射厚度恢复到真实值的9%以内。均匀幻象的CT重建中的不均匀性在较宽的光束能量和幻象几何形状范围内平均降低76%。
Quantitative reconstruction of cone beam X-ray computed tomography (CT) datasets requires accurate modeling of scatter, beam-hardening, beam profile, and detector response. Typically, commercial imaging systems use fast empirical corrections that are designed to reduce visible artifacts due to incomplete modeling of the image formation process. In contrast, Monte Carlo (MC) methods are much more accurate but are relatively slow. Scatter kernel superposition (SKS) methods offer a balance between accuracy and computational practicality. We show how a single SKS algorithm can be employed to correct both kilovoltage (kV) energy (diagnostic) and megavoltage (MV) energy (treatment) X-ray images. Using MC models of kV and MV imaging systems, we map intensities recorded on an amorphous silicon flat panel detector to water-equivalent thicknesses (WETs). Scatter-grams are derived from acquired projection images using scatter kernels indexed by the local WET values and are then iteratively refined using a scatter magnitude bounding scheme that allows the algorithm to accommodate the very high scatter-to-primary ratios encountered in kV imaging. The algorithm recovers radiological thicknesses to within 9% of the true value at both kV and megavolt energies. Nonuniformity in CT reconstructions of homogeneous phantoms is reduced by an average of 76% over a wide range of beam energies and phantom geometries.