Lipman Samantha L, Rouze Ned C, Palmeri Mark L, Nightingale Kathryn R
Duke University, Durham, NC 27708 USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2016 Aug;63(8):1049-1063. doi: 10.1109/TUFFC.2016.2558662. Epub 2016 Apr 27.
Shear waves propagating through interfaces where there is a change in stiffness cause reflected waves that can lead to artifacts in shear wave speed (SWS) reconstructions. Two-dimensional (2-D) directional filters are commonly used to reduce in-plane reflected waves; however, SWS artifacts arise from both in- and out-of-imaging-plane reflected waves. Herein, we introduce 3-D shear wave reconstruction methods as an extension of the previous 2-D estimation methods and quantify the reduction in image artifacts through the use of volumetric SWS monitoring and 4-D-directional filters. A Gaussian acoustic radiation force impulse excitation was simulated in phantoms with Young's modulus () of 3 kPa and a 5-mm spherical lesion with = 6, 12, or 18.75 kPa. The 2-D-, 3-D-, and 4-D-directional filters were applied to the displacement profiles to reduce in-and out-of-plane reflected wave artifacts. Contrast-to-noise ratio and SWS bias within the lesion were calculated for each reconstructed SWS image to evaluate the image quality. For 2-D SWS image reconstructions, the 3-D-directional filters showed greater improvements in image quality than the 2-D filters, and the 4-D-directional filters showed marginal improvement over the 3-D filters. Although 4-D-directional filters can further reduce the impact of large magnitude out-of-plane reflection artifacts in SWS images, computational overhead and transducer costs to acquire 3-D data may outweigh the modest improvements in image quality. The 4-D-directional filters have the largest impact in reducing reflection artifacts in 3-D SWS volumes.
剪切波在刚度发生变化的界面传播时会产生反射波，这可能导致剪切波速度（SWS）重建中出现伪像。二维（2-D）方向滤波器通常用于减少平面内反射波；然而，SWS伪像既来自成像平面内的反射波，也来自成像平面外的反射波。在此，我们引入三维剪切波重建方法，作为对先前二维估计方法的扩展，并通过使用体积SWS监测和四维方向滤波器来量化图像伪像的减少情况。在杨氏模量（）为3 kPa的体模以及具有= 6、12或18.75 kPa的5毫米球形病变中模拟高斯声辐射力脉冲激发。将二维、三维和四维方向滤波器应用于位移剖面，以减少平面内和平面外的反射波伪像。针对每个重建的SWS图像，计算病变内的对比度噪声比和SWS偏差，以评估图像质量。对于二维SWS图像重建，三维方向滤波器在图像质量上的改善比二维滤波器更大，而四维方向滤波器比三维滤波器有轻微改善。尽管四维方向滤波器可以进一步减少SWS图像中大幅度平面外反射伪像的影响，但获取三维数据的计算开销和换能器成本可能超过图像质量的适度改善。四维方向滤波器在减少三维SWS体积中的反射伪像方面影响最大。
