Institut Langevin, Ecole Superieure de Physique et de Chimie Industrielles de la Ville de Paris-ESPCI, ParisTech, Inserm U979, CNRS UMR7587, Universite Denis Diderot, France.
IEEE Trans Ultrason Ferroelectr Freq Control. 2012 Jul;59(7):1575-83. doi: 10.1109/TUFFC.2012.2357.
Focusing a wave through heterogeneous media is an important problem in medical ultrasound imaging. In such aberrating media, in the presence of a small number of point reflectors, iterative time reversal is a well-known method able to focus on the strongest reflector. However, in presence of speckle noise generated by many non-resolved scatterers, iterative time reversal alone does not work. In this paper, we propose the use of the echoes coming from moving particles in a flow, such as red blood cells, to generate a virtual point reflector by iterative time reversal. The construction of the virtual point reflector is performed by a coherent addition of independent realizations of speckle coming from moving particles. After focusing on a virtual point reflector, ultrasound images can be locally corrected inside an isoplanatic patch. An application for the correction of power Doppler images is presented. A theoretical analysis shows that this iterative method allows focusing on the point of maximal insonification of the uncorrected beam.
通过不均匀介质聚焦波是医学超声成象中的一个重要问题。在这种失常介质中，在存在少量点反射器的情况下，迭代时间反转是一种能够将焦点聚焦到最强反射器的已知方法。然而，在由许多未解析散射体产生的斑点噪声的情况下，单独的迭代时间反转是不起作用的。在本文中，我们提出利用流动中的运动粒子（如红细胞）的回波通过迭代时间反转来产生虚拟点反射器。虚拟点反射器的构造是通过对来自运动粒子的斑点的独立实现进行相干相加来完成的。在对虚拟点反射器进行聚焦之后，可以在等晕区内对超声图像进行局部校正。介绍了用于校正功率多普勒图像的应用。理论分析表明，这种迭代方法允许将焦点聚焦在未校正波束的最大照射点上。
