Hasegawa Hideyuki, Kanai Hiroshi
Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.
IEEE Trans Ultrason Ferroelectr Freq Control. 2008 Sep;55(9):1921-34. doi: 10.1109/TUFFC.884.
Atherosclerotic change of the arterial wall leads to a significant change in its elasticity. For assessment of elasticity, measurement of arterial wall deformation is required. For motion estimation, correlation techniques are widely used, and we have developed a phase-sensitive correlation method, namely, the phased-tracking method, to measure the regional strain of the arterial wall due to the heartbeat. Although phase-sensitive methods using demodulated complex signals require less computation in comparison with methods using the correlation between RF signals or iterative methods, the displacement estimated by such phase-sensitive methods are biased when the center frequency of the RF echo apparently varies. One of the reasons for the apparent change in the center frequency would be the interference of echoes from scatterers within the wall. In the present study, a method was introduced to reduce the influence of variation in the center frequencies of RF echoes on the estimation of the artery-wall strain when using the phase-sensitive correlation technique. The improvement in the strain estimation by the proposed method was validated using a phantom. The error from the theoretical strain profile and the standard deviation in strain estimated by the proposed method were 12.0% and 14.1%, respectively, significantly smaller than those (23.7% and 46.2%) obtained by the conventional phase-sensitive correlation method. Furthermore, in the preliminary in vitro experimental results, the strain distribution of the arterial wall well corresponded with pathology, i.e., the region with calcified tissue showed very small strain, and the region almost homogeneously composed of smooth muscle and collagen showed relatively larger strain and clear strain decay with respect to the radial distance from the lumen.
动脉壁的动脉粥样硬化改变会导致其弹性发生显著变化。为了评估弹性，需要测量动脉壁的变形。对于运动估计，相关技术被广泛使用，并且我们已经开发了一种相敏相关方法，即相位跟踪方法，来测量由于心跳引起的动脉壁区域应变。尽管与使用射频（RF）信号之间的相关性或迭代方法相比，使用解调复信号的相敏方法计算量较小，但当RF回波的中心频率明显变化时，通过这种相敏方法估计的位移会有偏差。中心频率出现明显变化的一个原因可能是来自壁内散射体的回波干扰。在本研究中，引入了一种方法来减少在使用相敏相关技术时RF回波中心频率变化对动脉壁应变估计的影响。使用体模验证了所提出方法在应变估计方面的改进。所提出方法估计的应变与理论应变分布的误差以及应变的标准偏差分别为12.0%和14.1%，明显小于传统相敏相关方法获得的误差（23.7%和46.2%）。此外，在初步的体外实验结果中，动脉壁的应变分布与病理学很好地对应，即钙化组织区域显示出非常小的应变，而几乎均匀由平滑肌和胶原蛋白组成的区域显示出相对较大的应变，并且相对于从管腔的径向距离有明显的应变衰减。
