Bottenus Nick B, Trahey Gregg E
Department of Biomedical Engineering, Duke University, Durham, North Carolina 27708.
J Acoust Soc Am. 2015 Jan;137(1):132-8. doi: 10.1121/1.4904530.
Ultrasonic echoes backscattered from diffuse media, recorded by an array transducer and appropriately focused, demonstrate coherence predicted by the van Cittert-Zernike theorem. Additive noise signals from off-axis scattering, reverberation, phase aberration, and electronic (thermal) noise can all superimpose incoherent or partially coherent signals onto the recorded echoes, altering the measured coherence. An expression is derived to describe the effect of uncorrelated random channel noise in terms of the noise-to-signal ratio. Equivalent descriptions are made in the aperture dimension to describe uncorrelated magnitude and phase apodizations of the array. Binary apodization is specifically described as an example of magnitude apodization and adjustments are presented to minimize the artifacts caused by finite signal length. The effects of additive noise are explored in short-lag spatial coherence imaging, an image formation technique that integrates the calculated coherence curve of acquired signals up to a small fraction of the array length for each lateral and axial location. A derivation of the expected contrast as a function of noise-to-signal ratio is provided and validation is performed in simulation.
由阵列换能器记录并适当聚焦的、从散射介质反向散射回来的超声回波，展现出了由范西特 - 泽尔尼克定理预测的相干性。来自离轴散射、混响、相位像差和电子（热）噪声的加性噪声信号，都可能将非相干或部分相干信号叠加到记录的回波上，从而改变测量到的相干性。推导了一个表达式，用于根据噪声与信号的比率来描述不相关随机通道噪声的影响。在孔径维度上进行了等效描述，以描述阵列的不相关幅度和相位切趾。具体描述了二元切趾作为幅度切趾的一个例子，并提出了调整方法，以最小化由有限信号长度引起的伪影。在短延迟空间相干成像中研究了加性噪声的影响，短延迟空间相干成像是一种图像形成技术，它针对每个横向和轴向位置，将采集信号的计算相干曲线积分到阵列长度的一小部分。给出了作为噪声与信号比率函数的预期对比度的推导，并在模拟中进行了验证。
