基于局部声速自适应波束形成的剪切波弹性成像相位畸变校正
Phase-Aberration Correction in Shear-wave Elastography Imaging Using Local Speed-of-Sound Adaptive Beamforming
摘要：
剪切波弹性成像（SWEI）是一种非侵入性成像方式，通过测量感应剪切波的传播速度来提供组织弹性信息。它在临床超声扫描仪上可商购获得，并广泛用于肝病和乳腺癌的诊断和分期。在传统的SWEI方法中，一系列的声辐射力（ARF）推动用于诱导剪切波，使用高帧速率多角度平面波成像（MA-PWI）跟踪剪切波以估计剪切波速（SWS）。传统上，假设先验已知且均匀的组织介质，使用恒定的声速（SoS）对这些平面波进行波束成形。然而，软组织是不均匀的，具有内在的SoS变化。在这项工作中，研究了SoS的影响和不均匀性对SWS估计，使用模拟和幻影实验猪肌肉作为abbarator，并显示如何使用本地声速自适应波束形成可以纠正这些像差。对于剪切波跟踪，我们比较标准波束形成与空间恒定的SoS值，软件波束形成与局部变化的SoS地图。我们表明，给定的SoS像差，传统的波束形成使用一个恒定的SoS，无论所利用的SoS值，引入了大量的偏差，在所得的SWS估计。当使用恒定SoS值时，观察到相同材料的平均SWS估计差异比使用已知SoS图进行波束成形时差4.3倍以上。这样的偏见被证明是通过使用波束成形中的局部SoS图来校正的，这表明了局部SoS重建技术的重要性和必要性。
英文摘要：
Shear-wave Elastography Imaging (SWEI) is a noninvasive imaging modality that provides tissue elasticity information by measuring the travelling speed of an induced shear-wave. It is commercially available on clinical ultrasound scanners and popularly used in the diagnosis and staging of liver disease and breast cancer. In conventional SWEI methods, a sequence of acoustic radiation force (ARF) pushes are used for inducing a shear-wave, which is tracked using high frame-rate multi-angle plane wave imaging (MA-PWI) to estimate the shear-wave speed (SWS). Conventionally, these plane waves are beamformed using a constant speed-of-sound (SoS), assuming an a-priori known and homogeneous tissue medium. However, soft tissues are inhomogeneous, with intrinsic SoS variations. In this work, study the SoS effects and inhomogeneities on SWS estimation, using simulation and phantoms experiments with porcine muscle as an abbarator, and show how these aberrations can be corrected using local speed-of-sound adaptive beamforming. For shear-wave tracking, we compare standard beamform with spatially constant SoS values to software beamforming with locally varying SoS maps. We show that, given SoS aberrations, traditional beamforming using a constant SoS, regardless of the utilized SoS value, introduces a substantial bias in resulting SWS estimations. Average SWS estimation disparity for the same material was observed over 4.3 times worse when a constant SoS value is used compared to that when a known SoS map is used for beamforming. Such biases are shown to be corrected by using a local SoS map in beamforming, indicating the importance of and a need for local SoS reconstruction techniques.
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