Fiducial marker-based correction for involuntary motion in weight-bearing C-arm CT scanning of knees. II. Experiment
Fiducial marker-based correction for involuntary motion in weight-bearing C-arm CT scanning of knees. II. Experiment
复制标题
DOI：
10.1118/1.4873675
复制
发表时间：
2014-06-01
期刊：
影响因子：
3.8
通讯作者：
Fahrig, Rebecca
中科院分区：
文献类型：
--
作者：
Choi, Jang-Hwan;Maier, Andreas;Fahrig, Rebecca
目的：C 型臂 CT 系统已被证明能够凭借其高度灵活的采集轨迹在负载条件下扫描单个尸体腿部。在本研究的第一部分中，使用基于 4D XCAT 的数值模拟，作者预测处于负重位置的受试者下半身的不自主运动会严重降低图像质量，并且作者提出了三种运动补偿方法，通过这些方法可以校正重建以提供诊断图像质量。在这里，作者证明平板血管造影系统适合在负重条件下对受试者的双腿进行体内扫描，并利用体内数据进一步评估三种运动校正算法。 方法：使用 PDS-2 体模对水平扫描轨迹的 C 形臂 CT 系统的几何形状进行校准。作者获取了两名健康志愿者仰卧在桌子上、站立和蹲在几个膝盖弯曲角度时的图像。为了识别下半身的不自主运动，在膝盖周围安装了 9 个直径 1 毫米的钽基准标记。 3D 中的静态平均标记位置（运动补偿的参考）是通过使用校准的投影矩阵在多个投影中对检测到的标记进行反投影并识别反投影光线的 3D 交点来估计的。使用三种不同的方法（之前详细描述过）来校正运动：(1) 2D 投影移位，(2) 2D 可变形投影扭曲，以及 (3) 3D 刚体扭曲。对于定量图像质量分析，使用仰卧数据作为基本事实来比较三种方法的 SSIM 指数。结果：基于 2D 欧氏距离的受试者运动度量范围为 0.85 毫米（+/- 0.49 毫米）到 3.82 毫米（+/- 2.91 毫米）（对应于 2.76 到 12.41 像素），导致 3D 重建中出现严重的运动伪影。在五个数据集（SCAN5）中运动最大的数据中，2D、2D 变形和 3D 变形的移动将中心切片的 SSIM 提高了 20.22%、16.83% 和 25.77%；偏心切片的改善分别为 18.94%、29.14% 和 36.08%。 结论：作者表明，C 臂 CT 控制可以针对非标准水平轨迹实施，这使我们能够扫描并成功重建处于负重位置的志愿者的双腿。正如使用理论模型预测的那样，所提出的运动校正方法通过减少重建中的运动伪影来提高图像质量； 3D 变形比 2D 方法表现更好，尤其是在偏心切片中。 (C) 2014 年美国医学物理学家协会。
Purpose: A C-arm CT system has been shown to be capable of scanning a single cadaver leg under loaded conditions by virtue of its highly flexible acquisition trajectories. In Part I of this study, using the 4D XCAT-based numerical simulation, the authors predicted that the involuntary motion in the lower body of subjects in weight-bearing positions would seriously degrade image quality and the authors suggested three motion compensation methods by which the reconstructions could be corrected to provide diagnostic image quality. Here, the authors demonstrate that a flat-panel angiography system is appropriate for scanning both legs of subjects in vivo under weight-bearing conditions and further evaluate the three motion-correction algorithms using in vivo data.Methods: The geometry of a C-arm CT system for a horizontal scan trajectory was calibrated using the PDS-2 phantom. The authors acquired images of two healthy volunteers while lying supine on a table, standing, and squatting at several knee flexion angles. In order to identify the involuntary motion of the lower body, nine 1-mm-diameter tantalum fiducial markers were attached around the knee. The static mean marker position in 3D, a reference for motion compensation, was estimated by back-projecting detected markers in multiple projections using calibrated projection matrices and identifying the intersection points in 3D of the back-projected rays. Motion was corrected using three different methods (described in detail previously): (1) 2D projection shifting, (2) 2D deformable projection warping, and (3) 3D rigid body warping. For quantitative image quality analysis, SSIM indices for the three methods were compared using the supine data as a ground truth.Results: A 2D Euclidean distance-based metric of subjects' motion ranged from 0.85 mm (+/- 0.49 mm) to 3.82 mm (+/- 2.91 mm) (corresponding to 2.76 to 12.41 pixels) resulting in severe motion artifacts in 3D reconstructions. Shifting in 2D, 2D warping, and 3D warping improved the SSIM in the central slice by 20.22%, 16.83%, and 25.77% in the data with the largest motion among the five datasets (SCAN5); improvement in off-center slices was 18.94%, 29.14%, and 36.08%, respectively.Conclusions: The authors showed that C-arm CT control can be implemented for nonstandard horizontal trajectories which enabled us to scan and successfully reconstruct both legs of volunteers in weight-bearing positions. As predicted using theoretical models, the proposed motion correction methods improved image quality by reducing motion artifacts in reconstructions; 3D warping performed better than the 2D methods, especially in off-center slices. (C) 2014 American Association of Physicists in Medicine.