Haddadin O S, Ebbini E S
Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor 48109, USA.
J Acoust Soc Am. 1998 Jul;104(1):313-25. doi: 10.1121/1.423291.
A new approach is introduced for self-focusing phased arrays through inhomogeneous media for therapeutic and imaging applications. This algorithm utilizes solutions to the inverse scattering problem to estimate the impulse response (Green's function) of the desired focal point(s) at the elements of the array. This approach is a two-stage procedure, where in the first stage the Green's functions is estimated from measurements of the scattered field taken outside the region of interest. In the second stage, these estimates are used in the pseudoinverse method to compute excitation weights satisfying predefined set of constraints on the structure of the field at the focus points. These scalar, complex valued excitation weights are used to modulate the incident field for retransmission. The pseudoinverse pattern synthesis method requires knowing the Green's function between the focus points and the array, which is difficult to attain for an unknown inhomogeneous medium. However, the solution to the inverse scattering problem, the scattering function, can be used directly to compute the required inhomogeneous Green's function. This inverse scattering based self-focusing is noninvasive and does not require a strong point scatterer at or near the desired focus point. It simply requires measurements of the scattered field outside the region of interest. It can be used for high resolution imaging and enhanced therapeutic effects through inhomogeneous media without making any assumptions on the shape, size, or location of the inhomogeneity. This technique is outlined and numerical simulations are shown which validate this technique for single and multiple focusing using a circular array.
本文介绍了一种用于治疗和成像应用的通过非均匀介质的自聚焦相控阵的新方法。该算法利用逆散射问题的解来估计阵列元件处所需焦点的脉冲响应（格林函数）。此方法分为两个阶段，在第一阶段，格林函数是根据在感兴趣区域之外测得的散射场来估计的。在第二阶段，这些估计值用于伪逆方法，以计算满足焦点处场结构预定义约束集的激励权重。这些标量复值激励权重用于调制入射场以便重新发射。伪逆方向图合成方法需要知道焦点与阵列之间的格林函数，对于未知的非均匀介质而言这很难获得。然而，逆散射问题的解，即散射函数，可直接用于计算所需的非均匀格林函数。这种基于逆散射的自聚焦是非侵入性的，并且不需要在期望焦点处或其附近有强点散射体。它仅需要在感兴趣区域之外测量散射场。它可用于通过非均匀介质进行高分辨率成像和增强治疗效果，而无需对不均匀性的形状、大小或位置做任何假设。本文概述了该技术，并展示了数值模拟结果，这些结果验证了该技术在使用圆形阵列进行单焦点和多焦点聚焦时的有效性。
