Medical UltraSound Imaging Center (MUSIC), Department of Radiology and Nuclear Medicine, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, The Netherlands.
Phys Med Biol. 2020 Apr 21;65(8):085007. doi: 10.1088/1361-6560/ab7b2f.
In ultrasound elastography, plane-wave acquisitions and angular displacement compounding (ADC) are often used and combined to allow high frame rates and to improve accuracy of lateral displacement estimates, respectively. This study investigates the performance of displacement and strain estimation for ADC as a function of; the main-to-grating-lobe-amplitude ratio which decreases as a function of steering angle; plane-wave acquisition and Delay-and-Sum (DaS)-related parameters; and grating-lobe filter cut-off frequency. Three experiments were conducted with a block phantom to test ADC performance for displacement fields of varying complexity: a lateral transducer shift, phantom rotation and phantom deformation. Experiments were repeated for four linear array transducers (pitch-to-lambda ratios between 0.6 and 1.4). Best ADC performance was found for steering angles that resulted in a theoretically derived main-to-grating-lobe-amplitude ratio of 1.7 dB for pure lateral translation and 6 dB for predominately lateral strain or rotation. Temporal filtering to reduce grating lobe signal or shifting of the receive aperture to receive angles below or above the optimal angle, as dictated by the main-to-grating-lobe-amplitude ratio, did not improve results. The accuracy of lateral displacement and strain estimates was improved by apodization in transmission and a dedicated F-number in DaS (0.75) allowing incidence angles within ± 33° in the active aperture. ADC with the optimized settings as found in this study improves the accuracy of displacements and strain estimates up to 80.7% compared to non-ADC. Compared to ADC settings described in current literature, our optimization improved the accuracy by 11.9% to 75.3% for lateral displacement and strain, and by 89.3% to 96.2% for rotation. The accuracy of ADC in rotation seemed to depend highly on plane-wave and DaS-related parameters which may explain the major improvement compared to settings in current literature. The overall improvement by optimized ADC was statistically significant compared to non-ADC (p = 0.003) and literature (p = 0.002).
在超声弹性成像中，平面波采集和角度位移复合（ADC）经常被使用和组合，以分别允许高帧率和提高横向位移估计的准确性。本研究调查了 ADC 的位移和应变估计性能，作为函数；主瓣-光栅瓣幅度比随转向角减小；平面波采集和延迟求和（DaS）相关参数；和光栅瓣滤波器截止频率。使用块体幻影进行了三个实验，以测试具有不同复杂性的位移场的 ADC 性能：横向换能器移位、幻影旋转和幻影变形。对于四个线性阵列换能器（间距-波长比在 0.6 到 1.4 之间）重复了实验。对于纯横向平移的理论推导的主瓣-光栅瓣幅度比为 1.7 dB，对于主要横向应变或旋转的理论推导的主瓣-光栅瓣幅度比为 6 dB 的转向角，ADC 性能最佳。为了减少光栅瓣信号，或根据主瓣-光栅瓣幅度比将接收孔径移动到接收角低于或高于最佳角度，进行了时间滤波，但这并没有改善结果。在传输中使用变迹和在 DaS 中使用专用 F 数（0.75）可以使入射角在有效孔径内的±33°以内，这提高了横向位移和应变估计的准确性。与非 ADC 相比，本研究中发现的优化 ADC 设置提高了位移和应变估计的准确性，最高可达 80.7%。与当前文献中描述的 ADC 设置相比，我们的优化将横向位移和应变的准确性提高了 11.9%至 75.3%，将旋转的准确性提高了 89.3%至 96.2%。ADC 在旋转中的准确性似乎高度依赖于平面波和 DaS 相关参数，这可以解释与当前文献中的设置相比的主要改进。与非 ADC（p = 0.003）和文献（p = 0.002）相比，优化 ADC 的整体改进具有统计学意义。
