Thompson Rosemary S, Macaskill Charlie, Padden Whayne
Centre for Mathematical Biology, School of Mathematics and Statistics, University of Sydney, Sydney, NSW 2006, Australia.
IEEE Trans Ultrason Ferroelectr Freq Control. 2009 Feb;56(2):304-13. doi: 10.1109/TUFFC.2009.1039.
Biomedical ultrasound is often used for investigations within and close to tissue inhomogeneities, such as lesions and plaques, that are midsized compared with the ultrasound wavelength. The scaled wavenumber is typically in the range 1 to 100. Even with small (less than 10%) sound speed variations, such objects are associated with very complicated diffractive field magnitude modulations. The corresponding phase modulations are much more regular, and this observation is the basis for the method described in this paper. The acoustic field can be expressed in terms of a scattering integral. For biomedical parameters, calculations with the widely used Born approximation give accurate results in only very limited circumstances. In this paper we demonstrate the importance of the initial phase estimate, and introduce the Phase Corrected Scattering Integral (PCSI) method. We show that remarkably accurate results for the acoustic field can be obtained from a single evaluation of the scattering integral if this incorporates an initial estimate of the phase modulation imposed by the inhomogeneity. A simple ray model can be used to find the phase correction. The PCSI method deals very effectively with scattering due to small changes in sound speed and irregular geometry, both characteristic of biomedical problems.
生物医学超声常用于对组织不均匀性内部及附近区域进行检测，这些不均匀性如病变和斑块，其尺寸与超声波长相比为中等大小。缩放波数通常在1到100的范围内。即使声速变化很小（小于10%），此类物体也会产生非常复杂的衍射场幅度调制。相应的相位调制则更为规则，这一观察结果是本文所描述方法的基础。声场可以用散射积分来表示。对于生物医学参数，使用广泛的玻恩近似进行计算仅在非常有限的情况下能给出准确结果。在本文中，我们证明了初始相位估计的重要性，并引入了相位校正散射积分（PCSI）方法。我们表明，如果散射积分包含由不均匀性引起的相位调制的初始估计值，那么通过对散射积分进行单次评估就能获得非常精确的声场结果。可以使用一个简单的射线模型来找到相位校正。PCSI方法能非常有效地处理由于声速微小变化和不规则几何形状引起的散射，这两者都是生物医学问题的特征。
