IEEE Trans Ultrason Ferroelectr Freq Control. 2011 Oct;58(10):2032-5. doi: 10.1109/TUFFC.2011.2052.
In recent years, novel quantitative techniques have been developed to provide noninvasive and quantitative stiffness images based on shear wave propagation. Using radiation force and ultrafast ultrasound imaging, the supersonic shear imaging technique allows one to remotely generate and follow a transient plane shear wave propagating in vivo in real time. The tissue shear modulus, i.e., its stiffness, can then be estimated from the shear wave local velocity. However, because the local shear wave velocity is estimated using a time-of- flight approach, reflected shear waves can cause artifacts in the estimated shear velocity because the incident and reflected waves propagate in opposite directions. Such effects have been reported in the literature as a potential drawback of elastography techniques based on shear wave speed, particularly in the case of high stiffness contrasts, such as in atherosclerotic plaque or stiff lesions. In this letter, we present our implementation of a simple directional filter, previously used for magnetic resonance elastography, which separates the forward- and backward-propagating waves to solve this problem. Such a directional filter could be applied to many elastography techniques based on the local estimation of shear wave speed propagation, such as acoustic radiation force imaging (ARFI), shearwave dispersion ultrasound vibrometry (SDUV), needle-based elastography, harmonic motion imaging, or crawling waves when the local propagation direction is known and high-resolution spatial and temporal data are acquired.
近年来，已经开发出了一些新的定量技术，以便基于剪切波传播提供非侵入性和定量的刚性图像。利用辐射力和超快超声成像，超声剪切波弹性成像技术可以远程产生和实时跟踪体内传播的瞬态平面剪切波。然后，可以根据剪切波局部速度来估计组织剪切模量，即其刚度。但是，由于局部剪切波速度是通过飞行时间方法来估计的，因此反射剪切波可能会导致估计的剪切速度出现伪影，因为入射波和反射波传播方向相反。在文献中已经报道了这种效应是基于剪切波速度的弹性成像技术的一个潜在缺点，特别是在高刚度对比度的情况下，例如在动脉粥样硬化斑块或刚性病变中。在这封信中，我们展示了我们对先前用于磁共振弹性成像的简单定向滤波器的实现，该滤波器可将正向和反向传播的波分离以解决此问题。这种定向滤波器可以应用于许多基于局部估计剪切波速度传播的弹性成像技术，例如声辐射力成像（ARFI）、剪切波频散超声振动计（SDUV）、基于针的弹性成像、谐波运动成像或爬行波，当局部传播方向已知且获得高分辨率的空间和时间数据时。
