Department of Medical Informatics, University Medical Center Hamburg-Eppendorf, Germany.
Int J Comput Assist Radiol Surg. 2010 Nov;5(6):595-605. doi: 10.1007/s11548-010-0418-7. Epub 2010 Apr 30.
Motivated by radiotherapy of lung cancer non- linear registration is applied to estimate 3D motion fields for local lung motion analysis in thoracic 4D CT images. Reliability of analysis results depends on the registration accuracy. Therefore, our study consists of two parts: optimization and evaluation of a non-linear registration scheme for motion field estimation, followed by a registration-based analysis of lung motion patterns.
The study is based on 4D CT data of 17 patients. Different distance measures and force terms for thoracic CT registration are implemented and compared: sum of squared differences versus a force term related to Thirion's demons registration; masked versus unmasked force computation. The most accurate approach is applied to local lung motion analysis.
Masked Thirion forces outperform the other force terms. The mean target registration error is 1.3 ± 0.2 mm, which is in the order of voxel size. Based on resulting motion fields and inter-patient normalization of inner lung coordinates and breathing depths a non-linear dependency between inner lung position and corresponding strength of motion is identified. The dependency is observed for all patients without or with only small tumors.
Quantitative evaluation of the estimated motion fields indicates high spatial registration accuracy. It allows for reliable registration-based local lung motion analysis. The large amount of information encoded in the motion fields makes it possible to draw detailed conclusions, e.g., to identify the dependency of inner lung localization and motion. Our examinations illustrate the potential of registration-based motion analysis.
受肺癌放射治疗的启发，将非线性配准应用于胸 4DCT 图像中局部肺运动分析以估计 3D 运动场。分析结果的可靠性取决于配准精度。因此，我们的研究包括两个部分：运动场估计的非线性配准方案的优化和评估，以及基于配准的肺运动模式分析。
该研究基于 17 名患者的 4DCT 数据。实现并比较了用于胸部 CT 配准的不同距离度量和力项：平方和差异与 Thirion 恶魔注册相关的力项；掩蔽与未掩蔽力计算。将最准确的方法应用于局部肺运动分析。
掩蔽 Thirion 力优于其他力项。平均目标配准误差为 1.3±0.2mm，处于体素大小的顺序。基于所得运动场以及内肺坐标和呼吸深度的患者间归一化，确定了内肺位置与相应运动强度之间的非线性依赖性。在没有或仅有小肿瘤的所有患者中都观察到这种依赖性。
对估计的运动场的定量评估表明具有较高的空间配准精度。它允许进行可靠的基于配准的局部肺运动分析。运动场中编码的大量信息使得可以得出详细的结论，例如，识别内肺定位和运动的依赖性。我们的检查说明了基于配准的运动分析的潜力。
