Zhang Zhijun, Ashraf Muhammad, Sahn David J, Song Xubo
Department of Biomedical Engineering, Oregon Health and Science University (OHSU), 3181 Southwest Sam Jackson Park Road, Portland, Oregon 97239.
Department of Pediatric Cardiology, Oregon Health and Science University, 3181 Southwest Sam Jackson Park Road, Portland, Oregon 97239.
Med Phys. 2014 May;41(5):052902. doi: 10.1118/1.4867864.
Quantitative analysis of cardiac motion is important for evaluation of heart function. Three dimensional (3D) echocardiography is among the most frequently used imaging modalities for motion estimation because it is convenient, real-time, low-cost, and nonionizing. However, motion estimation from 3D echocardiographic sequences is still a challenging problem due to low image quality and image corruption by noise and artifacts.
The authors have developed a temporally diffeomorphic motion estimation approach in which the velocity field instead of the displacement field was optimized. The optimal velocity field optimizes a novel similarity function, which we call the intensity consistency error, defined as multiple consecutive frames evolving to each time point. The optimization problem is solved by using the steepest descent method.
Experiments with simulated datasets, images of anex vivo rabbit phantom, images of in vivo open-chest pig hearts, and healthy human images were used to validate the authors' method. Simulated and real cardiac sequences tests showed that results in the authors' method are more accurate than other competing temporal diffeomorphic methods. Tests with sonomicrometry showed that the tracked crystal positions have good agreement with ground truth and the authors' method has higher accuracy than the temporal diffeomorphic free-form deformation (TDFFD) method. Validation with an open-access human cardiac dataset showed that the authors' method has smaller feature tracking errors than both TDFFD and frame-to-frame methods.
The authors proposed a diffeomorphic motion estimation method with temporal smoothness by constraining the velocity field to have maximum local intensity consistency within multiple consecutive frames. The estimated motion using the authors' method has good temporal consistency and is more accurate than other temporally diffeomorphic motion estimation methods.
心脏运动的定量分析对于评估心脏功能很重要。三维（3D）超声心动图是运动估计中最常用的成像方式之一，因为它方便、实时、低成本且无电离辐射。然而，由于图像质量低以及噪声和伪影导致的图像损坏，从3D超声心动图序列进行运动估计仍然是一个具有挑战性的问题。
作者开发了一种时间微分同胚运动估计方法，其中优化的是速度场而非位移场。最优速度场优化了一种新的相似性函数，我们称之为强度一致性误差，定义为多个连续帧向每个时间点演化。通过使用最速下降法解决优化问题。
使用模拟数据集、离体兔模型图像、活体开胸猪心脏图像和健康人体图像进行实验，以验证作者的方法。模拟和真实心脏序列测试表明，作者方法的结果比其他竞争的时间微分同胚方法更准确。超声测微法测试表明，跟踪的晶体位置与地面真值具有良好的一致性，并且作者的方法比时间微分同胚自由形式变形（TDFFD）方法具有更高的准确性。使用公开获取的人体心脏数据集进行验证表明，作者的方法比TDFFD和逐帧方法具有更小的特征跟踪误差。
作者提出了一种通过约束速度场在多个连续帧内具有最大局部强度一致性来实现具有时间平滑性的微分同胚运动估计方法。使用作者方法估计的运动具有良好的时间一致性，并且比其他时间微分同胚运动估计方法更准确。
