Hasegawa Hideyuki, Kanai Hiroshi
Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.
IEEE Trans Ultrason Ferroelectr Freq Control. 2006 Nov;53(11):2050-64. doi: 10.1109/tuffc.2006.145.
Noninvasive measurement of mechanical properties, such as elasticity, of the arterial wall, is useful for diagnosis of atherosclerosis. For assessment of mechanical properties, it is necessary to measure the deformation of the arterial wall. In this study, a modification of the previously proposed phased-tracking method was conducted to improve measurement of the small change in thickness (deformation) of the arterial wall due to the heartbeat. In our previous method, a set of two points along an ultrasonic beam was initially assigned, and the change in thickness of the layer between these two points during an entire cardiac cycle was estimated. In motion estimation with ultrasound, the motion of an interface or a scatterer, which generates an echo, can be obtained by estimating the change in time delay of the echo. For example, in the case of a carotid artery of a healthy subject, there are only two dominant echoes from the lumen-intima and media-adventitia interfaces. Thus, only the displacements of the lumen-intima and media-adventitia interfaces can be estimated, which means that ultrasound can estimate only the change in distance (thickness) between these two interfaces. However, even in this case, our previous method gives different estimates of the change in thickness, depending on the depths (positions in the arterial radial direction) of the two initially assigned points. In this study, modifications of the previous method in terms of the strategy for assignment of layers and the required thickness of an assigned layer were made to reduce such an artificial spatial variation in the estimated changes in thickness. Using the proposed method, errors in estimated changes in thickness were reduced from 21.2 +/- 24.1% to 0.19 +/- 0.04% (mean +/- standard deviation) in simulation experiments. As in the case of the simulation experiments, the spatial variation in estimated changes in thickness also was reduced in in vivo experiments in a carotid artery of a healthy subject and in vitro experiments using two excised, diseased arteries.
无创测量动脉壁的力学特性，如弹性，对动脉粥样硬化的诊断很有用。为了评估力学特性，有必要测量动脉壁的变形。在本研究中，对先前提出的相位跟踪方法进行了改进，以改善因心跳导致的动脉壁厚度微小变化（变形）的测量。在我们之前的方法中，最初沿着超声束指定一组两个点，并估计这两个点之间的层在整个心动周期中的厚度变化。在超声运动估计中，产生回波的界面或散射体的运动可以通过估计回波时间延迟的变化来获得。例如，对于健康受试者的颈动脉，仅从管腔 - 内膜和中膜 - 外膜界面有两个主要回波。因此，只能估计管腔 - 内膜和中膜 - 外膜界面的位移，这意味着超声只能估计这两个界面之间距离（厚度）的变化。然而，即使在这种情况下，我们之前的方法根据最初指定的两个点的深度（动脉径向位置）给出不同的厚度变化估计。在本研究中，对先前方法在层分配策略和分配层所需厚度方面进行了修改，以减少估计厚度变化中的这种人为空间变化。在模拟实验中，使用所提出的方法，估计厚度变化的误差从21.2±24.1%降低到0.19±0.04%（平均值±标准差）。与模拟实验的情况一样，在健康受试者颈动脉的体内实验和使用两根切除的病变动脉的体外实验中，估计厚度变化的空间变化也减少了。
