Université de Lyon, Creatis, CNRS UMR 5220, INSERM U630, Université Lyon 1, INSA-Lyon, France.
Ultrasonics. 2010 Jun;50(7):683-90. doi: 10.1016/j.ultras.2010.01.008. Epub 2010 Jan 25.
Ultrasonic imaging is often used to estimate blood flow velocity. Currently, estimates are carried out using Doppler-based techniques. However, there are a number of shortcomings such as the limited spatial resolution and the inability to estimate longitudinal flows. Thus, alternative methods have been proposed to overcome them. Difficulties are notably encountered with high-frequency imaging systems that use swept-scan techniques. In this article, we propose to compare four vector velocity estimation methods that are complementary to Doppler, focusing on 40 MHz, high-frequency imaging. The goal of this study is to evaluate which method could circumvent the limitations of Doppler methods for evaluation of microcirculation, in the vessels having diameter on the order of 1 mm. We used two region-based approaches, one decorrelation-based approach and one spatiotemporal approach. Each method has been applied to seven flow sequences with various orientations and mean velocities. Four sequences were simulated with a system approach based on a 3D set of moving scatterers. Three experimental sequences were carried out by injecting blood-mimicking fluid within a gelatin phantom and then acquiring images with Visualsonics, Vevo 660 system. From velocity estimates, several performance criteria such as the normalized mean error or the normalized mean standard deviation were defined to compare the performance of the four estimators. The results show that region-based methods are the most accurate exhibiting mean errors less than 10% and mean standard deviation less than 13%. However, region-based approaches are those that require the highest calculative cost compared to the decorrelation-based method, which is the fastest. Finally, the spatiotemporal approach appeared to be a trade-off in terms of computational complexity and accuracy of estimates. It provides estimates with errors less than 10% for mean velocity and the CPU time is approximately 17s for a ROI of size 40*80 pixels.
超声成像是一种常用的血流速度估计方法。目前，主要采用基于多普勒的技术进行血流速度估计。然而，这些方法存在一些局限性，例如空间分辨率有限，无法估计纵向血流等。因此，已经提出了一些替代方法来克服这些问题。在使用扫频技术的高频成像系统中，存在着一些特别的困难。在本文中，我们提出了四种与多普勒互补的矢量速度估计方法，重点关注 40MHz 的高频成像。该研究的目的是评估哪种方法可以克服多普勒方法在评估直径约为 1mm 的血管微循环方面的局限性。我们使用了两种基于区域的方法、一种基于去相关的方法和一种时空方法。每种方法都应用于具有不同方向和平均流速的七个流速序列。其中四个序列是通过基于三维运动散射体的系统方法模拟的。三个实验序列是通过在明胶模型中注入血液模拟液并使用 Visualsonics 的 Vevo 660 系统获取图像来完成的。从速度估计中，定义了一些性能指标，如归一化平均误差或归一化平均标准差，以比较四个估计器的性能。结果表明，基于区域的方法是最准确的，其平均误差小于 10%，平均标准差小于 13%。然而，与基于去相关的方法相比，基于区域的方法需要更高的计算成本，而基于去相关的方法是最快的。最后，时空方法在计算复杂性和估计精度方面似乎是一种权衡。它可以提供平均误差小于 10%的估计值，对于大小为 40*80 像素的 ROI，CPU 时间约为 17s。
