Chen Hao, Varghese Tomy
Department of Medical Physics, The University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
Med Phys. 2009 Jun;36(6):2098-106. doi: 10.1118/1.3121426.
Two-dimensional (2D) cross-correlation algorithms are necessary to estimate local displacement vector information for strain imaging. However, most of the current two-dimensional cross-correlation algorithms were developed for linear array transducers. Although sector and phased array transducers are routinely used for clinical imaging of abdominal and cardiac applications, strain imaging for these applications has been performed using one-dimensional (1D) cross-correlation analysis. However, one-dimensional cross-correlation algorithms are unable to provide accurate and precise strain estimation along all the angular insonification directions which can range from -45 degrees to 45 degrees with sector and phased array transducers. In addition, since sector and phased array based images have larger separations between beam lines as the pulse propagates deeper into tissue, signal decorrelation artifacts with deformation or tissue motion are more pronounced. In this article, the authors propose a multilevel two-dimensional hybrid algorithm for ultrasound sector and phased array data that demonstrate improved tracking and estimation performance when compared to the traditional 1D cross-correlation or 2D cross-correlation based methods. Experimental results demonstrate that the signal-to-noise and contrast-to-noise ratio estimates improve significantly for smaller window lengths for the hybrid method when compared to the currently used one-dimensional or two-dimensional cross-correlation algorithms. Strain imaging results on ex vivo thermal lesions created in liver tissue and in vivo on cardiac short-axis views demonstrate the improved image quality obtained with this method.
二维（2D）互相关算法对于应变成像中局部位移矢量信息的估计是必要的。然而，当前大多数二维互相关算法是为线性阵列换能器开发的。尽管扇形和相控阵换能器常用于腹部和心脏应用的临床成像，但这些应用的应变成像一直使用一维（1D）互相关分析。然而，一维互相关算法无法沿着所有角度的声束入射方向提供准确而精确的应变估计，扇形和相控阵换能器的角度范围可以从-45度到45度。此外，由于基于扇形和相控阵的图像在脉冲向组织深处传播时，波束线之间的间距更大，因此与变形或组织运动相关的信号去相关伪像更为明显。在本文中，作者提出了一种用于超声扇形和相控阵数据的多级二维混合算法，与传统的基于1D互相关或2D互相关的方法相比，该算法展示出了更好的跟踪和估计性能。实验结果表明，与当前使用的一维或二维互相关算法相比，对于混合方法，在较小窗口长度下，信噪比和对比噪声比估计有显著提高。在肝组织中创建的离体热损伤以及心脏短轴视图的体内应变成像结果证明了该方法获得了更好的图像质量。
