Background and Objective: Left ventricle (LV) dysfunction always occurs at early heart-failure stages, producing variations in the LV flow patterns. Cardiac diagnostics may therefore benefit from flow-pattern analysis. Several visualization tools have been proposed that require ultrafast ultrasound acquisitions. However, ultrafast ultrasound is not standard in clinical scanners. Meanwhile techniques that can handle low frame rates are still lacking. As a result, the clinical translation of these techniques remains limited, especially for 3D acquisitions where the volume rates are intrinsically low.

Methods: To overcome these limitations, we propose a novel technique for the estimation of LV blood velocity and relative-pressure fields from dynamic contrast-enhanced ultrasound (DCE-US) at low frame rates. Different from other methods, our method is based on the time-delays between time-intensity curves measured at neighbor pixels in the DCE-US loops. Using Navier-Stokes equation, we regularize the obtained velocity fields and derive relative-pressure estimates. Blood flow patterns were characterized with regard to their vorticity, relative-pressure changes (dp/dt) in the LV outflow tract, and viscous energy loss, as these reflect the ejection efficiency.

Results: We evaluated the proposed method on 18 patients (9 responders and 9 non-responders) who underwent cardiac resynchronization therapy (CRT). After CRT, the responder group evidenced a significant (p<0.05) increase in vorticity and peak dp/dt, and a non-significant decrease in viscous energy loss. No significant difference was found in the non-responder group. Relative feature variation before and after CRT evidenced a significant difference (p<0.05) between responders and non-responders for vorticity and peak dp/dt. Finally, the method feasibility is also shown with 3D DCE-US.

Conclusions: Using the proposed method, adequate visualization and quantification of blood flow patterns are successfully enabled based on low-rate DCE-US of the LV, facilitating the clinical adoption of the method using standard ultrasound scanners. The clinical value of the method in the context of CRT is also shown.

背景与目的：左心室功能障碍总是发生在心力衰竭的早期，从而导致左心室血流模式的变化。因此，心脏诊断可能会受益于流型分析。已经提出了几种需要超快速超声采集的可视化工具。但是，超快超声在临床扫描仪中不是标准的。同时，仍然缺乏能够处理低帧速率的技术。结果，这些技术的临床翻译仍然受到限制，特别是对于体积率本质上较低的3D采集。

方法：为了克服这些局限性，我们提出了一种新技术，用于在低帧频下从动态对比增强超声（DCE-US）估计左室血流速度和相对压力场。与其他方法不同，我们的方法基于在DCE-US回路中相邻像素处测得的时间强度曲线之间的时间延迟。使用Navier-Stokes方程，我们对获得的速度场进行正则化，并得出相对压力估计值。根据其涡度，左室流出道的相对压力变化（dp / dt）和粘性能量损失来表征血流模式，因为它们反映了喷射效率。

结果：我们对18例接受了心脏再同步治疗（CRT）的患者（9名有反应者和9名无反应者）进行了评估。CRT后，响应者组证明涡度和峰值dp / dt显着增加（p <0.05），粘性能量损失无明显降低。在无反应组中没有发现显着差异。CRT前后的相对特征变化表明响应者和非响应者之间的涡度和峰值dp / dt差异显着（p <0.05）。最后，在3D DCE-US中也显示了该方法的可行性。

结论：使用所提出的方法，可以基于低速率的LV的DCE-US成功实现对血流模式的充分可视化和量化，从而有助于使用标准超声扫描仪对该方法进行临床采用。还显示了在CRT情况下该方法的临床价值。