Shear wave arrival time estimates correlate with local speckle pattern.
Shear wave arrival time estimates correlate with local speckle pattern.
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DOI：
10.1109/tuffc.2015.007171
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发表时间：
2015-12
期刊：
影响因子：
--
通讯作者：
Langdon J
中科院分区：
文献类型：
--
作者：
Mcaleavey SA;Osapoetra LO;Langdon J
我们给出的模拟和模型研究表明，在具有充分发展的散斑的目标中，剪切波到达时间估计的误差与局部散斑图案的横向位置之间具有很强的相关性。我们假设观测到的到达时间变化在很大程度上是由于潜在的散斑图案造成的，并将这种效应称为散斑偏差。到达时间估计是定量剪切波弹性成像的关键步骤，通过射频超声回波的互相关或类似方法来跟踪组织运动。散射体强度的变化和来自跟踪波束内散射体的回波的干扰导致回波不一定描述波束内的平均运动，而是有利于建设性干扰和强散射的区域。通过固定发射光束并将接收孔径扫过感兴趣区域而形成的扫描接收图像被用来估计局部散斑图案。在模拟和模体中，散斑横向位置的度量被发现与估计的横波到达时间有很强的相关性(r>；0.7)。扫描-接收模式的横向加权改善了到达时间估计和散斑位置之间的相关性。仿真表明，高的射频回波相关性并不等于精确的横波到达时间估计--高的相关系数表明运动被高精度地跟踪，但跟踪的位置在跟踪波束宽度内是不确定的。强的轴上散斑的存在被认为意味着高的射频相关性和低的偏置。相反，似乎不是这样--高度相关的射频回波仍然可以产生有偏差的到达时间估计。与沿给定跟踪矢量获得不同散斑实现的变化相比，横波到达时间偏差随横波幅度和符号的变化(模拟−20μm到20μm)相对稳定。我们发现，与轴向位置/局部散斑图案的变化相比，到达时间偏差与剪切波幅度的依赖关系较弱。模拟了发射光圈为f/3至f/8，接收光圈为f/2和f/4。到达时间误差和与散斑图案的相关性最强烈地取决于接收孔径。
We present simulation and phantom studies demonstrating a strong correlation between errors in shear wave arrival time estimates and the lateral position of the local speckle pattern in targets with fully developed speckle. We hypothesize that the observed arrival time variations are largely due to the underlying speckle pattern, and call the effect speckle bias. Arrival time estimation is a key step in quantitative shear wave elastography, performed by tracking tissue motion via cross correlation of RF ultrasound echoes or similar methods. Variations in scatterer strength and interference of echoes from scatterers within the tracking beam result in an echo that does not necessarily describe the average motion within the beam, but one favoring areas of constructive interference and strong scattering. A swept-receive image, formed by fixing the transmit beam and sweeping the receive aperture over the region of interest, is used to estimate the local speckle pattern. Metrics for the lateral position of the speckle are found to correlate strongly (r>0.7) with the estimated shear wave arrival times both in simulations and in phantoms. Lateral weighting of the swept-receive pattern improved the correlation between arrival time estimates and speckle position. The simulations indicate that high RF echo correlation does not equate to an accurate shear wave arrival time estimate – a high correlation coefficient indicates that motion is being tracked with high precision, but the location tracked is uncertain within the tracking beam width. The presence of a strong on-axis speckle is seen to imply high RF correlation and low bias. The converse does not appear to be true – highly correlated RF echoes can still produce biased arrival time estimates. The shear wave arrival time bias is relatively stable with variations in shear wave amplitude and sign (−20 μm to 20 μm simulated) compared to the variation with different speckle realizations obtained along a given tracking vector. We show that the arrival time bias is weakly dependent on shear wave amplitude compared to the variation with axial position/local speckle pattern. Apertures of f/3 to f/8 on transmit and f/2 and f/4 on receive were simulated. Arrival time error and correlation with speckle pattern are most strongly determined by the receive aperture.