Jansen M J A, Kuijf H J, Veldhuis W B, Wessels F J, van Leeuwen M S, Pluim J P W
Center for Image Sciences, University Medical Center Utrecht, Utrecht, Netherlands.
Phys Med Biol. 2017 Sep 12;62(19):7556-7568. doi: 10.1088/1361-6560/aa8848.
Motion correction of 4D dynamic contrast enhanced MRI (DCE-MRI) series is required for diagnostic evaluation of liver lesions. The registration, however, is a challenging task, owing to rapid changes in image appearance. In this study, two different registration approaches are compared; a conventional pairwise method applying mutual information as metric and a groupwise method applying a principal component analysis based metric, introduced by Huizinga et al (2016). The pairwise method transforms the individual 3D images one by one to a reference image, whereas the groupwise registration method computes the metric on all the images simultaneously, exploiting the temporal information, and transforms all 3D images to a common space. The performance of the two registration methods was evaluated using 70 clinical 4D DCE-MRI series with the focus on the liver. The evaluation was based on the smoothness of the time intensity curves in lesions, lesion volume change after deformation and the smoothness of spatial deformation. Furthermore, the visual quality of subtraction images (pre-contrast image subtracted from the post contrast images) before and after registration was rated by two observers. Both registration methods improved the alignment of the DCE-MRI images in comparison to the non-corrected series. Furthermore, the groupwise method achieved better temporal alignment with smoother spatial deformations than the pairwise method. The quality of the subtraction images was graded satisfactory in 32% of the cases without registration and in 77% and 80% of the cases after pairwise and groupwise registration, respectively. In conclusion, the groupwise registration method outperforms the pairwise registration method and achieves clinically satisfying results. Registration leads to improved subtraction images.
4D动态对比增强磁共振成像（DCE-MRI）系列的运动校正对于肝脏病变的诊断评估是必需的。然而，由于图像外观的快速变化，配准是一项具有挑战性的任务。在本研究中，比较了两种不同的配准方法；一种是应用互信息作为度量的传统成对方法，另一种是应用由Huizinga等人（2016年）提出的基于主成分分析的度量的组内方法。成对方法将各个3D图像逐一变换到参考图像，而组内配准方法利用时间信息同时在所有图像上计算度量，并将所有3D图像变换到一个公共空间。使用70个临床4D DCE-MRI系列评估了两种配准方法的性能，重点是肝脏。评估基于病变中时间强度曲线的平滑度、变形后病变体积的变化以及空间变形的平滑度。此外，由两名观察者对配准前后的减法图像（从对比后图像中减去对比前图像）的视觉质量进行评分。与未校正的系列相比，两种配准方法都改善了DCE-MRI图像的对齐。此外，与成对方法相比，组内方法实现了更好的时间对齐，空间变形更平滑。在未配准的情况下，32%的病例中减法图像质量被评为满意，而成对配准和组内配准后分别有77%和80%的病例被评为满意。总之，组内配准方法优于成对配准方法，并取得了临床满意的结果。配准导致减法图像得到改善。
