Medical Radiation Sciences, University of Sydney, NSW 2141, Australia.
Med Phys. 2013 Apr;40(4):041903. doi: 10.1118/1.4794481.
To establish a practical and accurate motion tracking method for the development of rigid motion correction methods in helical x-ray computed tomography (CT).
A commercially available optical motion tracking system provided 6 degrees of freedom pose measurements at 60 Hz. A 4 × 4 calibration matrix was determined to convert raw pose data acquired in tracker coordinates to a fixed CT coordinate system with origin at the isocenter of the scanner. Two calibration methods, absolute orientation (AO), and a new method based on image registration (IR), were compared by means of landmark analysis and correlation coefficient in phantom images coregistered using the derived motion transformations.
Transformations calculated using the IR-derived calibration matrix were found to be more accurate, with positional errors less than 0.5 mm (mean RMS), and highly correlated image voxel intensities. The AO-derived calibration matrix yielded larger mean RMS positional errors (≈ 1.0 mm), and poorer correlation coefficients.
The authors have demonstrated the feasibility of accurate motion tracking for retrospective motion correction in helical CT. Their new IR-based calibration method based on image registration and function minimization was simpler to perform and delivered more accurate calibration matrices. This technique is a useful tool for future work on rigid motion correction in helical CT and potentially also other imaging modalities.
建立一种实用且精确的运动跟踪方法，以开发螺旋 X 射线计算机断层扫描（CT）中的刚性运动校正方法。
使用市售的光学运动跟踪系统以 60 Hz 的频率提供 6 自由度位姿测量。确定了一个 4×4 的校准矩阵，将在跟踪器坐标系中获取的原始位姿数据转换为以扫描仪等中心为原点的固定 CT 坐标系。通过对使用所得到的运动变换进行配准的体模图像中的标志点分析和相关系数，比较了绝对取向（AO）和基于图像配准（IR）的新方法两种校准方法。
使用 IR 推导的校准矩阵计算出的变换被发现更准确，位置误差小于 0.5 毫米（均方根 RMS），并且图像体素强度高度相关。AO 推导的校准矩阵产生的 RMS 位置误差较大（约 1.0 毫米），并且相关系数较差。
作者已经证明了在螺旋 CT 中进行回顾性运动校正的精确运动跟踪的可行性。他们基于图像配准和函数最小化的新的基于 IR 的校准方法更简单，并且提供了更精确的校准矩阵。这项技术是在螺旋 CT 中进行刚性运动校正以及潜在地其他成像方式的未来工作的有用工具。
