Jaeger Michael, Robinson Elise, Akarçay H Günhan, Frenz Martin
Institute of Applied Physics, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.
Phys Med Biol. 2015 Jun 7;60(11):4497-515. doi: 10.1088/0031-9155/60/11/4497. Epub 2015 May 19.
Aberrations of the acoustic wave front, caused by spatial variations of the speed-of-sound, are a main limiting factor to the diagnostic power of medical ultrasound imaging. If not accounted for, aberrations result in low resolution and increased side lobe level, over all reducing contrast in deep tissue imaging. Various techniques have been proposed for quantifying aberrations by analysing the arrival time of coherent echoes from so-called guide stars or beacons. In situations where a guide star is missing, aperture-based techniques may give ambiguous results. Moreover, they are conceptually focused on aberrators that can be approximated as a phase screen in front of the probe. We propose a novel technique, where the effect of aberration is detected in the reconstructed image as opposed to the aperture data. The varying local echo phase when changing the transmit beam steering angle directly reflects the varying arrival time of the transmit wave front. This allows sensing the angle-dependent aberration delay in a spatially resolved way, and thus aberration correction for a spatially distributed volume aberrator. In phantoms containing a cylindrical aberrator, we achieved location-independent diffraction-limited resolution as well as accurate display of echo location based on reconstructing the speed-of-sound spatially resolved. First successful volunteer results confirm the clinical potential of the proposed technique.
由声速的空间变化引起的声波前畸变是医学超声成像诊断能力的主要限制因素。如果不加以考虑，畸变会导致分辨率降低和旁瓣电平增加，总体上会降低深部组织成像的对比度。已经提出了各种技术，通过分析来自所谓的引导星或信标的相干回波的到达时间来量化畸变。在没有引导星的情况下，基于孔径的技术可能会给出模糊的结果。此外，它们在概念上侧重于可以近似为探头前方相位屏的像差器。我们提出了一种新颖的技术，与孔径数据相反，在重建图像中检测像差的影响。改变发射波束转向角时变化的局部回波相位直接反映了发射波前变化的到达时间。这允许以空间分辨的方式感测与角度相关的像差延迟，从而对空间分布的体积像差器进行像差校正。在包含圆柱形像差器的体模中，我们基于空间分辨的声速重建，实现了与位置无关的衍射极限分辨率以及回波位置的准确显示。首次成功的志愿者结果证实了所提出技术的临床潜力。
