Steinberg B D
Valley Forge Research Center, Moore School of Electrical Engineering, University of Pennsylvania, Philadelphia 19104.
Ultrason Imaging. 1992 Oct;14(4):387-97. doi: 10.1177/016173469201400405.
This review paper discusses the basic properties of two adaptive signal processing procedures for dealing with weak scattering in a phased array transducer system. A fundamental improvement in the lateral resolution of ultrasonic echo scanners will result if the weight vector of a large phased array transducer can be modified to account for distortion in the propagation medium. Lateral resolution in most tissue is limited to a few mm by wavefront-distortion-induced sound-speed variations. One important wavefront-distortion source is scattering from local speed variations within large and reasonably homogeneous tissue beds such as the liver. Scattering disperses some energy from the beam and perturbs the wavefront, thereby distorting the image and limiting the resolution to the scale of the distortion. Often, such scattering is weak, meaning that most of the energy in the beam is unscattered. The total field at the receiving transducer is the vector sum of the unscattered and scattered fields. In weak scattering the unscattered field is dominant and the resultant field can be treated as the unscattered field plus a perturbation. The net effect is primarily a distorted phasefront, while the amplitude or modulus of the wavefront remains reasonably intact. Refraction and strong scattering effect the wavefront more severely and are less responsive to these algorithms.
这篇综述论文讨论了相控阵换能器系统中用于处理弱散射的两种自适应信号处理程序的基本特性。如果能够修改大型相控阵换能器的权重向量以考虑传播介质中的畸变，超声回波扫描仪的横向分辨率将得到根本性的提高。在大多数组织中，由于波前畸变引起的声速变化，横向分辨率被限制在几毫米以内。一个重要的波前畸变源是来自大的且相当均匀的组织床（如肝脏）内局部速度变化的散射。散射会使波束中的一些能量分散，并扰乱波前，从而使图像失真，并将分辨率限制在畸变的尺度上。通常，这种散射很弱，这意味着波束中的大部分能量没有被散射。接收换能器处的总场是未散射场和散射场的矢量和。在弱散射中，未散射场占主导地位，合成场可以被视为未散射场加上一个微扰。净效应主要是波前畸变，而波前的幅度或模量基本保持不变。折射和强散射对波前的影响更为严重，并且对这些算法的响应较小。
