Spatial coherence of backscatter for the nonlinearly produced second harmonic for specific transmit apodizations
Spatial coherence of backscatter for the nonlinearly produced second harmonic for specific transmit apodizations
复制标题
DOI：
10.1109/tuffc.2004.1302766
复制
发表时间：
2004-05-01
影响因子：
3.6
通讯作者：
Miller, JG
中科院分区：
文献类型：
--
作者：
Fedewa, RJ;Wallace, KD;Miller, JG
为了获得成功，基于相关性的相位畸变校正需要后向散射信号之间的高度相关性。对于谐波成像，二次谐波分量的反向散射的空间相干性不同于基波分量的反向散射的空间相干性。这项工作的目的是确定的影响，改变发射切趾的空间相干性的后向散射的非线性产生的二次谐波。我们的方法是使用实验测量和模拟来确定基波和二次谐波的有效切趾。利用水听器对矩形和圆形孔板产生的有限振幅超声场的横截面进行了二维测量。研究了三种不同的一维发射切趾函数：均匀、Riesz和梯形。对于每个发射切趾，通过反向传播使用线性角谱方法从发射聚焦区内测量的值来获得有效的切趾。使用脉冲回波货车Cittert-Zernike定理获得后向散射的空间相干性的预测。在所有情况下，2f处的有效变迹比发射变迹窄。我们证明，某些传输切趾的结果在一个更大的空间相干性的后向散射在第二谐波比在基本。
To be successful, correlation-based, phaseaberration correction requires a high correlation among backscattered signals. For harmonic imaging, the spatial coherence of backscatter for the second harmonic component is different than the spatial coherence of backscatter for the fundamental component. The purpose of this work was to determine the effect of changing the transmit apodization on the spatial coherence of backscatter for the nonlinearly generated second harmonic. Our approach was to determine the effective apodizations for the fundamental and second harmonic using both experimental measurements and simulations. Two-dimensional measurements of the transverse cross sections of the finite-amplitude ultrasonic fields generated by rectangular and circular apertures were acquired with a hydrophone. Three different one-dimensional transmit apodization functions were investigated: uniform, Riesz, and trapezoidal. An effective apodization was obtained for each transmit apodization by backpropagating the values measured from within the transmit focal zone using a linear angular spectrum approach. Predictions of the spatial coherence of backscatter were obtained using the pulse-echo Van Cittert-Zernike theorem. In all cases the effective apodization at 2f was narrower than the transmit apodization. We demonstrate that certain transmit apodizations result in a greater spatial coherence of backscatter at the second harmonic than at the fundamental.