Nonrigid registration methods for measuring regional left atrial motion using retrospective gated CT images

房颤（AF）患者的心房纤维化会降低心房收缩力，增加心房壁硬度。局部心房变形可用应变和应变率测量。MRI特征跟踪（FT）和超声心动图斑点跟踪用于测量心房应变，并且在文献中发现这两种方式的应变测量表明局部纤维化。然而，回声衍生的应变测量通常使用2D成像进行，这无法捕获完整的心房运动并损害应变测量。MR图像通常具有与左房壁厚度相同数量级的平面内空间分辨率，这可能会降低成像和跟踪左房心内膜边界的可信度。在这个项目中，我们建议使用高分辨率对比度增强的回顾性门控CT图像来测量心房壁的三维变形。我们计划优化时间稀疏自由形式变形（TSFFD）和体素变形（Voxel Morph）方法来跟踪门控CT图像中的左心房运动。为了为LA解剖创建注册错误，我们将在初始心脏阶段创建LA分割和表面网格，并将这些变形到后续阶段。随后阶段的分割和网格为变形的输出提供了“接地真相”。全局指标（平均表面距离、骰子得分系数和豪斯多夫距离）和局部指标（PV点与质心之间的点对点误差）将用于量化配准精度。5倍交叉验证将用于微调配准方法参数，以避免对数据的过拟合并实现泛化性能。我们将使用通用心房坐标系统计算区域LA应变（面积和纤维应变），并比较有和无房颤的心力衰竭患者之间的应变。

Atrial fibrosis in patients suffering from atrial fibrillation (AF) is known to decrease atrial contractility and increase atrial wall stiffness. Regional atrial deformation can be measured using strain and strain rate. MRI feature tracking (FT) and echocardiography speckle tracking are used to measure atrial strain, and both modalities' strain measurements have been found to indicate local fibrosis in the literature. However, echo-derived strain measurements are often performed using 2D imaging, which fails to capture full atrial motion and compromises the strain measurements. MR images typically have in-plane spatial resolution of the same order as left atrial wall thickness, which may reduce confidence in imaging and tracking the left atrial endocardial border. In this project we propose to use high resolution contrast-enhanced retrospective gated CT images to measure atrial wall deformation in 3D. We plan to optimise the Temporal Sparse Free Form Deformation (TSFFD) and Voxel Morph methods to track left atrial (LA) motion in gated CT images. In order to create registration errors for the LA anatomy, we will create LA segmentations and surface meshes at the initial cardiac phase, and deform these to the proceeding phases. Segmentations and meshes at subsequent phases provide a 'ground truth' to the deformed outputs. Global metrics (average surface distance, dice score coefficient and Hausdorff distance) and local metrics (point-to-point errors between PV ostia centre of mass) will be used to quantify the registration accuracy. 5-fold cross validation will be used to fine-tune the registration method parameters to avoid overfitting to data and achieve generalised performance. We will calculate regional LA strains (area and fibre strains) using the Universal Atrial Coordinate system, and compare strains between heart failure patients with and without AF.