In this paper we propose a method for locally adjusted optical flow-based registration of multimodal images, which uses the segmentation of object of interest and its representation by the signed-distance function (OF$ ^{dist} $ method). We deal with non-rigid registration of the image series acquired by the Modiffied Look-Locker Inversion Recovery (MOLLI) magnetic resonance imaging sequence, which is used for a pixel-wise estimation of $ T_1 $ relaxation time. The spatial registration of the images within the series is necessary to compensate the patient's imperfect breath-holding. The evolution of intensities and a large variation of image contrast within the MOLLI image series, together with the myocardium of left ventricle (the object of interest) typically not being the most distinct object in the scene, makes the registration challenging. The paper describes all components of the proposed OF$ ^{dist} $ method and their implementation. The method is then compared to the performance of a standard mutual information maximization-based registration method, applied either to the original image (MIM) or to the signed-distance function (MIM$ ^{dist} $). Several experiments with synthetic and real MOLLI images are carried out. On synthetic image with a single object, MIM performed the best, while OF$ ^{dist} $ and MIM$ ^{dist} $ provided better results on synthetic images with more than one object and on real images. When applied to signed-distance function of two objects of interest, MIM$ ^{dist} $ provided a larger registration error, but more homogeneously distributed, compared to OF$ ^{dist} $. For the real MOLLI image series with left ventricle pre-segmented using a level-set method, the proposed OF$ ^{dist} $ registration performed the best, as is demonstrated visually and by measuring the increase of mutual information in the object of interest and its neighborhood.

中文翻译：

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基于符号距离函数的图像强度变化的图像序列的非刚性配准

在本文中，我们提出了一种基于局部调整的基于光流的多模态图像配准方法，该方法使用感兴趣对象的分割及其通过符号距离函数的表示（OF $ ^ {dist} $方法）。我们处理由Modiffied Look-Locker反转恢复（MOLLI）磁共振成像序列获取的图像序列的非刚性配准，该序列用于按像素估算$ T_1 $弛豫时间。系列内图像的空间配准对于补偿患者不完美的屏气是必要的。MOLLI图像系列中强度的演变和图像对比度的较大变化，以及通常不是场景中最明显的对象的左心室心肌（感兴趣的对象），使得配准极具挑战性。本文介绍了提议的OF $ ^ {dist} $方法的所有组件及其实现。然后将该方法与应用于原始图像（MIM）或有符号距离函数（MIM $ ^ {dist} $）的基于标准互信息最大化的注册方法的性能进行比较。使用合成的和真实的MOLLI图像进行了一些实验。在具有单个对象的合成图像上，MIM表现最佳，而OF $ ^ {dist} $和MIM $ ^ {dist} $在具有多个对象的合成图像和真实图像上提供更好的结果。与OF $ ^ {dist} $相比，当将MIM $ ^ {dist} $应用于两个感兴趣对象的符号距离函数时，提供了更大的配准误差，但分布更均匀。对于使用水平集方法预先分割了左心室的真实MOLLI图像系列，