Maltz Jonathan S, Gangadharan Bijumon, Bose Supratik, Hristov Dimitre H, Faddegon Bruce A, Paidi Ajay, Bani-Hashemi Ali R
Oncology Care Systems Group, Siemens Medical Solutions (USA), Inc., Concord, CA 94520, USA.
IEEE Trans Med Imaging. 2008 Dec;27(12):1791-810. doi: 10.1109/TMI.2008.928922.
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). Scattergrams 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.
锥束X射线计算机断层扫描（CT）数据集的定量重建需要对散射、束硬化、束轮廓和探测器响应进行精确建模。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产生的可见伪影。相比之下，蒙特卡罗（MC）方法要精确得多，但相对较慢。散射核叠加（SKS）方法在准确性和计算实用性之间取得了平衡。我们展示了如何使用单一的SKS算法来校正千伏（kV）能量（诊断）和兆伏（MV）能量（治疗）的X射线图像。使用kV和MV成像系统的MC模型，我们将非晶硅平板探测器上记录的强度映射到水等效厚度（WET）。散射图是从采集的投影图像中使用由局部WET值索引的散射核得出的，然后使用散射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射与原发射线比。该算法在kV和兆伏能量下将放射学厚度恢复到真实值的9%以内。在广泛的束能量和体模几何形状范围内，均匀体模的CT重建中的不均匀性平均降低了76%。
