Phase aberration in transcranial ultrasound imaging (TUI) caused by the human skull leads to an inaccurate image reconstruction. In this article, we present a novel method for estimating the speed of sound and an adaptive beamforming technique for phase aberration correction in a flat polyvinylchloride (PVC) slab as a model for the human skull. First, the speed of sound of the PVC slab is found by extracting the overlapping quasi-longitudinal wave velocities of symmetrical Lamb waves in the frequency–wavenumber domain. Then, the thickness of the plate is determined by the echoes from its front and back side. Next, an adaptive beamforming method is developed, utilizing the measured sound speed map of the imaging medium. Finally, to minimize reverberation artifacts caused by strong scatterers (i.e., needles), a dual probe setup is proposed. In this setup, we image the medium from two opposite directions, and the final image can be the minimum intensity projection of the inherently co-registered images of the opposed probes. Our results confirm that the Lamb wave method estimates the longitudinal speed of the slab with an error of 3.5% and is independent of its shear wave speed. Benefiting from the acquired sound speed map, our adaptive beamformer reduces (in real time) a mislocation error of 3.1, caused by an 8 mm slab, to 0.1 mm. Finally, the dual probe configuration shows 7 dB improvement in removing reverberation artifacts of the needle, at the cost of only 2.4-dB contrast loss. The proposed image formation method can be used, e.g., to monitor deep brain stimulation procedures and localization of the electrode(s) deep inside the brain from two temporal bones on the sides of the human skull.

中文翻译：

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兰姆波和自适应波束形成在医学超声成像中的像差校正

由人类颅骨引起的经颅超声成像（TUI）中的相差导致图像重建不准确。在本文中，我们介绍了一种用于估计声速的新颖方法和一种用于人头骨模型的扁平聚氯乙烯（PVC）平板中用于相差校正的自适应波束形成技术。首先，通过在频率-波数域中提取对称兰姆波的重叠准纵波速度来确定PVC板的声速。然后，板的厚度由其正面和背面的回波确定。接下来，利用测得的成像介质的声速图来开发自适应波束形成方法。最后，为了最大程度地减少由强散射体（例如，针头）引起的混响伪影，提出了双探头设置。在这种设置中，我们从两个相反的方向对介质成像，最终图像可以是相对探针固有共配图像的最小强度投影。我们的结果证实，兰姆波法估计板坯的纵向速度误差为3.5％，并且与剪切波速度无关。得益于所获取的声速图，我们的自适应波束形成器（实时）将8毫米厚板引起的3.1位置误差降低到0.1毫米。最终，双探头配置在去除针的混响伪影方面显示出7 dB的改善，而对比度损失仅为2.4 dB。可以使用所提出的图像形成方法，例如，