Department of Electronic Engineering, Information School, Yunnan University, Kunming, Yunnan, 650091, China.
Department of Cardiovascular, The Second Affiliated Hospital of Kunming Medical University, Kunming, Yunnan, 650031, China.
Med Phys. 2018 Jan;45(1):131-143. doi: 10.1002/mp.12678. Epub 2017 Dec 10.
A dynamic ultrasound simulation model for the common carotid artery (CCA) with three arterial layers for validation of two-dimensional wall motion and blood velocity estimation algorithms is proposed in the present study. This model describes layers with not only characteristics of echo distributions conforming to clinical ones but also varying thicknesses, axial, and radial displacements with pulsatile blood pressure during a cardiac cycle.
The modeling process is as follows: first, a geometrical model according with the clinical structure size of a CCA is built based on the preset layer thicknesses and the diameter of lumen. Second, a three-dimensional scatterer model is constructed by a mapping with a Hilbert space-filling curve from the one-dimensional scatterer distribution with the position and amplitude following Gamma and Gaussian distributions, respectively. The characteristics of three layers and blood are depicted by smoothly adjusting the scatterer density, the scale, and shape parameters of the Gamma distribution as well as the mean and standard deviation of the Gaussian distribution. To obtain the values of parameters of scatterer distributions, including the shape parameter, density, and intensity, for arterial layers and blood, the envelope signals simulated from different configurations of scatterer distribution are compared with those from different kinds of tissue of CCAs in vivo through a statistic analysis. Finally, the dynamic scatterer model is realized based on the blood pressure, elasticity modulus of intima-media (IM) and adventitia, varying IM thickness, axial displacement of IM as well as blood flow velocity at central axis during a cardiac cycle. Then, the corresponding radiofrequency (RF) signals, envelope signals, and B-mode images of the pulsatile CCA are generated in a dynamic scanning mode using Field II platform.
The three arterial layers, blood, and surrounding tissue in simulated B-mode ultrasound images are clearly legible. The results based on a statistical analysis for the envelope signals from 30 simulations indicate that the echo characteristics of blood, intima, media, and adventitia are in accordant with clinical ones. The maximum relative errors between the preset geometrical sizes and the measured ones from the simulated images for the diameter of the lumen and the thicknesses of the intima, media, and adventitia are 0.13%, 3.89%, 1.35%, and 0.06%, respectively. For the dynamic parameters, the variation in IM thickness, the radial displacements of lumen and adventitia as well as the axial displacement of IM and blood flow velocity are measured with the mean relative errors of 68.03%, 9.27%, 2.10%, 4.93%, and 17.34%, respectively.
The simulated results present static sizes and dynamical variations according with preset values; echo distributions conforming to clinical versions. Therefore, the presented simulation model could be useful as a data source to evaluate the performance of studies on measurements of ultrasound-based tissue structures and dynamic parameters for the CCA layers.
本研究提出了一种用于验证二维壁运动和血流速度估计算法的颈总动脉（CCA）三层动态超声模拟模型。该模型不仅描述了符合临床回声分布特征的各层，还描述了在心动周期中随脉动血压变化的各层厚度、轴向和径向位移。
建模过程如下：首先，根据预设的层厚和管腔直径，建立符合 CCA 临床结构尺寸的几何模型。其次，通过希尔伯特空间填充曲线从一维散射体分布构建三维散射体模型，位置和幅度分别服从伽马和高斯分布。通过平滑调整伽马分布的散射体密度、比例和形状参数以及高斯分布的均值和标准差来描述三层和血液的特征。为了获得动脉层和血液的散射体分布参数值，包括形状参数、密度和强度，通过统计分析将从不同散射体分布配置模拟的包络信号与体内不同类型的 CCA 组织进行比较。最后，根据心动周期中的血压、内中膜（IM）和外膜的弹性模量、IM 厚度变化、IM 轴向位移以及中心轴上的血流速度，实现动态散射体模型。然后，在 Field II 平台上以动态扫描模式生成脉动 CCA 的相应射频（RF）信号、包络信号和 B 模式图像。
模拟 B 模式超声图像中清晰可辨三层动脉、血液和周围组织。基于 30 次模拟的包络信号的统计分析结果表明，血液、内膜、中膜和外膜的回声特征与临床一致。模拟图像中管腔直径和内膜、中膜和外膜厚度的预设几何尺寸与测量尺寸之间的最大相对误差分别为 0.13%、3.89%、1.35%和 0.06%。对于动态参数，IM 厚度、管腔和外膜的径向位移以及 IM 和血流速度的轴向位移的变化，测量的平均相对误差分别为 68.03%、9.27%、2.10%、4.93%和 17.34%。
模拟结果呈现出符合预设值的静态尺寸和动态变化；符合临床版本的回声分布。因此，所提出的模拟模型可作为评估基于超声的组织结构和 CCA 层动态参数测量研究性能的数据源。
