3D Non-Rigid Alignment of Low-Dose Scans Allows to Correct for Saturation in Lower Extremity Cone-Beam CT.
3D Non-Rigid Alignment of Low-Dose Scans Allows to Correct for Saturation in Lower Extremity Cone-Beam CT.
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DOI：
10.1109/access.2021.3079368
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Choi JH
中科院分区：
文献类型：
--
作者：
Maier J;Maier A;Eskofier B;Fahrig R;Choi JH
当使用自动曝光控制（AEC）系统对高度变化的形状和材料组成的物体成像时，锥束计算机断层扫描中的检测器饱和就会发生。当成像对象的膝盖时，高光束能量确保内部结构的可见性，但会导致在密度较低的边缘区域过度曝光。在这项工作中，我们建议使用额外的低剂量扫描来纠正AEC扫描的饱和伪影。在AEC扫描的投影图像中使用基于直方图的阈值来识别过度曝光的像素。在体积重建之前，AEC扫描的无饱和像素与低剂量扫描的皮肤边界像素相结合。为了补偿患者在两次扫描之间的运动，提出了基于基准标记位置的前后投影过程中投影图像的三维非刚性对齐。在数值模拟中，投影组合将结构相似指数从0.883提高到0.999。进一步的评估是对两个体内受试者的膝关节进行的，一个没有，一个在AEC和低剂量扫描之间运动。使用波束衰减器获得无饱和参考图像。该方法可以定性地恢复周围组织结构信息。应用三维非刚性对齐，可以使用具有扫描主体间运动的投影图像进行投影图像组合。由于额外的低剂量扫描而增加的辐射暴露是可以忽略不计的。提出的方法允许简单而有效的校正饱和伪影。
Detector saturation in cone-beam computed tomography occurs when an object of highly varying shape and material composition is imaged using an automatic exposure control (AEC) system. When imaging a subject’s knees, high beam energy ensures the visibility of internal structures but leads to overexposure in less dense border regions. In this work, we propose to use an additional low-dose scan to correct the saturation artifacts of AEC scans. Overexposed pixels are identified in the projection images of the AEC scan using histogram-based thresholding. The saturation-free pixels from the AEC scan are combined with the skin border pixels of the low-dose scan prior to volumetric reconstruction. To compensate for patient motion between the two scans, a 3D non-rigid alignment of the projection images in a backward-forward-projection process based on fiducial marker positions is proposed. On numerical simulations, the projection combination improved the structural similarity index measure from 0.883 to 0.999. Further evaluations were performed on two in vivo subject knee acquisitions, one without and one with motion between the AEC and low-dose scans. Saturation-free reference images were acquired using a beam attenuator. The proposed method could qualitatively restore the information of peripheral tissue structures. Applying the 3D non-rigid alignment made it possible to use the projection images with inter-scan subject motion for projection image combination. The increase in radiation exposure due to the additional low-dose scan was found to be negligibly low. The presented methods allow simple but effective correction of saturation artifacts.
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