Ormachea Juvenal, Castaneda Benjamin, Parker Kevin J
Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York, USA.
Laboratorio de Imagenes Medicas, Pontificia Universidad Catolica del Peru, Lima, Peru.
Ultrasound Med Biol. 2018 May;44(5):963-977. doi: 10.1016/j.ultrasmedbio.2018.01.011. Epub 2018 Feb 21.
Elastography is a modality that estimates tissue stiffness and, thus, provides useful information for clinical diagnosis. Attention has focused on the measurement of shear wave propagation; however, many methods assume shear wave propagation is unidirectional and aligned with the lateral imaging direction. Any deviations from the assumed propagation result in biased estimates of shear wave speed. To address these challenges, directional filters have been applied to isolate shear waves with different propagation directions. Recently, a new method was proposed for tissue stiffness estimation involving creation of a reverberant shear wave field propagating in all directions within the medium. These reverberant conditions lead to simple solutions, facile implementation and rapid viscoelasticity estimation of local tissue. In this work, this new approach based on reverberant shear waves was evaluated and compared with another well-known elastography technique using two calibrated elastic and viscoelastic phantoms. Additionally, the clinical feasibility of this technique was analyzed by assessing shear wave speed in human liver and breast tissues, in vivo. The results indicate that it is possible to estimate the viscoelastic properties in each scanned medium. Moreover, a better approach to estimation of shear wave speed was obtained when only the phase information was taken from the reverberant waves, which is equivalent to setting all magnitudes within the bandpass equal to unity: an idealization of a perfectly isotropic reverberant shear wave field.
弹性成像技术是一种估计组织硬度的方法，因此可为临床诊断提供有用信息。目前的研究重点是剪切波传播的测量；然而，许多方法假设剪切波传播是单向的且与横向成像方向对齐。与假设传播的任何偏差都会导致剪切波速度估计出现偏差。为应对这些挑战，已应用方向滤波器来分离具有不同传播方向的剪切波。最近，有人提出了一种新的组织硬度估计方法，该方法涉及在介质中创建一个向各个方向传播的混响剪切波场。这些混响条件导致了简单的解决方案、易于实现以及对局部组织的快速粘弹性估计。在这项工作中，基于混响剪切波的这种新方法使用两个校准的弹性和粘弹性体模进行了评估，并与另一种著名的弹性成像技术进行了比较。此外，通过在体内评估人体肝脏和乳腺组织中的剪切波速度，分析了该技术的临床可行性。结果表明，可以估计每个扫描介质中的粘弹性特性。此外，当仅从混响波中获取相位信息时，获得了一种更好的剪切波速度估计方法，这相当于将带通内的所有幅度设置为 unity：一个完美各向同性混响剪切波场的理想化。
