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

已知患有心房颤动（AF）的患者的心房纤维化降低心房收缩力并增加心房壁硬度。局部心房变形可以使用应变和应变率来测量。MRI特征跟踪（FT）和超声心动图斑点跟踪用于测量心房应变，文献中发现这两种方式的应变测量均指示局部纤维化。然而，回波衍生的应变测量通常使用2D成像来执行，这无法捕获完整的心房运动并损害应变测量。MR图像通常具有与左心房壁厚度相同数量级的平面内空间分辨率，这可能降低成像和跟踪左心房内膜边界的置信度。在本项目中，我们建议使用高分辨率对比增强回顾性门控CT图像来测量3D心房壁变形。我们计划优化时间稀疏自由变形（TSFFD）和体素形态方法，以跟踪门控CT图像中的左心房（LA）运动。为了创建左心房解剖结构的配准误差，我们将在初始心脏相位创建左心房分割和表面网格，并将其变形为后续相位。后续阶段的分段和网格为变形输出提供了“地面实况”。将使用全局指标（平均表面距离、骰子得分系数和Hausdorff距离）和局部指标（肺静脉口质心之间的点对点误差）来量化配准准确度。5-将使用折叠交叉验证来微调配准方法参数，以避免对数据的过拟合并实现通用性能。我们将使用通用心房坐标系计算局部LA应变（面积和纤维应变），并比较有AF和无AF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.