Mellema Daniel C, Song Pengfei, Kinnick Randall R, Urban Matthew W, Greenleaf James F, Manduca Armando, Chen Shigao
IEEE Trans Med Imaging. 2016 Sep;35(9):2098-106. doi: 10.1109/TMI.2016.2550007. Epub 2016 Apr 4.
Ultrasound shear wave elastography (SWE) utilizes the propagation of induced shear waves to characterize the shear modulus of soft tissue. Many methods rely on an acoustic radiation force (ARF) "push beam" to generate shear waves. However, specialized hardware is required to generate the push beams, and the thermal stress that is placed upon the ultrasound system, transducer, and tissue by the push beams currently limits the frame-rate to about 1 Hz. These constraints have limited the implementation of ARF to high-end clinical systems. This paper presents Probe Oscillation Shear Elastography (PROSE) as an alternative method to measure tissue elasticity. PROSE generates shear waves using a harmonic mechanical vibration of an ultrasound transducer, while simultaneously detecting motion with the same transducer under pulse-echo mode. Motion of the transducer during detection produces a "strain-like" compression artifact that is coupled with the observed shear waves. A novel symmetric sampling scheme is proposed such that pulse-echo detection events are acquired when the ultrasound transducer returns to the same physical position, allowing the shear waves to be decoupled from the compression artifact. Full field-of-view (FOV) two-dimensional (2D) shear wave speed images were obtained by applying a local frequency estimation (LFE) technique, capable of generating a 2D map from a single frame of shear wave motion. The shear wave imaging frame rate of PROSE is comparable to the vibration frequency, which can be an order of magnitude higher than ARF based techniques. PROSE was able to produce smooth and accurate shear wave images from three homogeneous phantoms with different moduli, with an effective frame rate of 300 Hz. An inclusion phantom study showed that increased vibration frequencies improved the accuracy of inclusion imaging, and allowed targets as small as 6.5 mm to be resolved with good contrast (contrast-to-noise ratio ≥ 19 dB) between the target and background.
超声剪切波弹性成像（SWE）利用诱导剪切波的传播来表征软组织的剪切模量。许多方法依靠声辐射力（ARF）“推束”来产生剪切波。然而，产生推束需要专门的硬件，并且推束施加在超声系统、换能器和组织上的热应力目前将帧率限制在约1Hz。这些限制使得ARF仅应用于高端临床系统。本文提出了探头振荡剪切弹性成像（PROSE）作为一种测量组织弹性的替代方法。PROSE利用超声换能器的谐波机械振动产生剪切波，同时在脉冲回波模式下用同一换能器检测运动。检测过程中换能器的运动会产生与观察到的剪切波耦合的“应变样”压缩伪像。提出了一种新颖的对称采样方案，使得在超声换能器回到相同物理位置时采集脉冲回波检测事件，从而使剪切波与压缩伪像解耦。通过应用局部频率估计（LFE）技术获得全场（FOV）二维（2D）剪切波速度图像，该技术能够从单帧剪切波运动生成2D图。PROSE的剪切波成像帧率与振动频率相当，这可能比基于ARF的技术高一个数量级。PROSE能够从三个具有不同模量的均匀体模中产生平滑且准确的剪切波图像，有效帧率为300Hz。一项包含体模研究表明，增加振动频率可提高包含物成像的准确性，并能分辨小至6.5mm的目标，目标与背景之间具有良好的对比度（对比度噪声比≥19dB）。
