Hajim School of Engineering and Applied Sciences, Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2012 Aug;59(8):1639-53. doi: 10.1109/TUFFC.2012.2370.
Noninvasive elastography (NIVE) produces elastograms that are difficult to interpret because NIVE visualizes strain in the transducer coordinate system. In this paper, we hypothesized that transforming normal and shear strain elastograms to the vessel coordinate system will produce better strain elastograms. To corroborate this hypothesis, we acquired synthetic-aperture (SA) ultrasound data from simulated and physical vessel phantoms. In both studies, SA echo frames were reconstructed from data acquired with a sparse transducer array. The simulation study was performed with homogeneous and heterogenous phantoms, but in the experimental study we used a modified ultrasound scanner to acquire SA data from homogeneous (n = 1) and heterogeneous (n = 3) vessel phantoms. Axial and lateral displacements were estimated by performing two-dimensional cross-correlation analysis on the beamformed RF echo frames. We generated radial and circumferential strain elastograms by transforming normal and shear strain elastograms to the vessel coordinate system. The results revealed: 1) radial and circumferential strain elastograms acquired from simulated data had a relative root mean squared error on the order of 0.1%; 2) experimentally acquired radial and circumferential strain elastograms had elastographic contrast-to-noise ratio (CNRe) between 10 and 40 dB, and elastographic signal-to-noise ratio (SNRe) between 10 and 35 dB, depending on the number of active transmission elements employed during imaging; 3) radial and circumferential strain elastograms produced with fewer than 8 active transmission elements were inferior to those computed with a greater number of active elements; and 4) plaques were evident in the strain elastograms, except in those obtained with the sparsest transducer array. This study demonstrated that a syntheticaperture ultrasound system could visualize radial and circumferential strain noninvasively.
无创弹性成像（NIVE）产生的弹性图像较难解释，因为 NIVE 是在换能器坐标系中可视化应变。在本文中，我们假设将正常应变和剪切应变弹性图像转换到血管坐标系中会产生更好的应变弹性图像。为了验证这一假设，我们从模拟和物理血管体模中获取了合成孔径（SA）超声数据。在这两项研究中，SA 回波帧都是从稀疏换能器阵列采集的数据中重建的。模拟研究使用均匀和不均匀体模进行，但在实验研究中，我们使用修改后的超声扫描仪从均匀（n=1）和不均匀（n=3）血管体模中获取 SA 数据。轴向和横向位移是通过对波束形成的 RF 回波帧进行二维互相关分析来估计的。我们通过将正常应变和剪切应变弹性图像转换到血管坐标系来生成径向和周向应变弹性图像。结果表明：1）从模拟数据获得的径向和周向应变弹性图像的相对均方根误差在 0.1%左右；2）实验获得的径向和周向应变弹性图像的弹性对比噪声比（CNRe）在 10 到 40dB 之间，弹性信号噪声比（SNRe）在 10 到 35dB 之间，这取决于成像过程中使用的活动发射元件的数量；3）使用少于 8 个活动发射元件生成的径向和周向应变弹性图像不如使用更多活动元件计算的图像；4）除了使用最稀疏的换能器阵列获得的图像外，应变弹性图像中都可以看到斑块。本研究表明，合成孔径超声系统可以无创可视化径向和周向应变。
