Rodriguez-Molares Alfonso, Løvstakken Lasse, Ekroll Ingvild Kinn, Torp Hans
Department of Circulation and Medical Imaging (ISB), Norwegian University of Science and Technology, 7491 Trondheim, Norway.
J Acoust Soc Am. 2015 Sep;138(3):1365-78. doi: 10.1121/1.4928036.
A method is presented to reconstruct the geometry of specular reflectors with an ultrasonic array based on the image source principle. The ultrasonic beam is focused at a point in space emulating a point source within the medium. The transmitted wave interacts with the specular reflector and propagates back to the array as if it were generated by an image source. The reflected wave is analyzed with a sound source localization algorithm to estimate the image source location, and the reflector geometry is extracted using the mirror equation for spherical reflectors. The method is validated experimentally and its accuracy is studied. Under ideal conditions the method provides an accurate reconstruction of the position, orientation, and radius of curvature of specular reflectors, with errors Δr < 0.2 mm, Δα < 3°, and ΔR/R0 < 0.2, respectively. The method performs very well in the presence of high levels of thermal and speckle noise, with no degradation of the reconstruction as long as SNR(th) > -3 dB (signal-to-thermal-noise ratio) and SNR(sp) > 7 dB (signal-to-speckle-noise ratio). An iterative scheme based on the proposed method is presented to reconstruct the geometry of arbitrary reflectors by subdividing the reflector boundary into smaller segments. The iterative scheme is demonstrated both numerically and experimentally.
提出了一种基于图像源原理用超声阵列重建镜面反射器几何形状的方法。超声束聚焦于介质内模拟点源的空间中的一点。发射波与镜面反射器相互作用并传播回阵列，就好像它是由一个图像源产生的。用声源定位算法分析反射波以估计图像源位置，并使用球面反射器的镜像方程提取反射器几何形状。该方法通过实验进行了验证，并研究了其准确性。在理想条件下，该方法能准确重建镜面反射器的位置、方向和曲率半径，误差分别为Δr < 0.2 mm、Δα < 3°和ΔR/R0 < 0.2。该方法在存在高水平热噪声和散斑噪声的情况下表现良好，只要信噪比(SNR(th)) > -3 dB（信号与热噪声比）且信噪比(SNR(sp)) > 7 dB（信号与散斑噪声比），重建效果就不会下降。提出了一种基于该方法的迭代方案，通过将反射器边界细分为更小的段来重建任意反射器的几何形状。通过数值和实验演示了该迭代方案。
