van Dongen Koen W A, Wright William M D
Ultrasonics Research Group, Department of Electrical and Electronic Engineering, University College Cork, College Road, Cork, Ireland.
J Acoust Soc Am. 2007 Mar;121(3):1538-49. doi: 10.1121/1.2431333.
Imaging the two acoustic medium parameters density and compressibility requires the use of both the acoustic pressure and velocity wave fields, described via integral equations. Imaging is based on solving for the unknown medium parameters using known measured scattered wave fields, and it is difficult to solve this ill-posed inverse problem directly using a conjugate gradient inversion scheme. Here, a contrast source inversion method is used in which the contrast sources, defined via the product of changes in compressibility and density with the pressure and velocity wave fields, respectively, are computed iteratively. After each update of the contrast sources, an update of the medium parameters is obtained. Total variation as multiplicative regularization is used to minimize blurring in the reconstructed contrasts. The method successfully reconstructed three-dimensional contrast profiles based on changes in both density and compressibility, using synthetic data both with and without 50% white noise. The results were compared with imaging based only on the pressure wave field, where speed of sound profiles were solely based on changes in compressibility. It was found that the results improved significantly by using the full vectorial method when changes in speed of sound depended on changes in both compressibility and density.
对两种声学介质参数（密度和可压缩性）进行成像需要使用通过积分方程描述的声压和速度波场。成像基于利用已知的测量散射波场求解未知的介质参数，而直接使用共轭梯度反演方案来求解这个不适定的反问题是困难的。在此，使用了一种对比源反演方法，其中通过可压缩性和密度的变化分别与压力和速度波场的乘积定义的对比源是迭代计算的。在每次更新对比源之后，获得介质参数的更新。使用总变分作为乘法正则化来最小化重建对比中的模糊。该方法使用有和没有50%白噪声的合成数据成功地基于密度和可压缩性的变化重建了三维对比剖面。将结果与仅基于压力波场的成像进行了比较，在仅基于压力波场的成像中，声速剖面仅基于可压缩性的变化。结果发现，当声速变化取决于可压缩性和密度两者的变化时，使用全矢量方法结果有显著改善。
