Department of Electronic Engineering, Sogang University, Seoul, Korea.
IEEE Trans Ultrason Ferroelectr Freq Control. 2012 May;59(5):905-14. doi: 10.1109/TUFFC.2012.2275.
In ultrasound exams of obese patients and the breast, the spatial and contrast resolutions of ultrasound images are severely deteriorated when a constant sound speed corresponding to soft tissue is used in receive dynamic beamformation. This degradation is due to the defocusing of the ultrasound beam because of the disparity in sound speed between soft tissue and fatty layers. To minimize the degradation, this paper proposes a new method of estimating an optimal sound speed that can be used to achieve the best beamforming performance in a region of interest (ROI). The proposed method employs a new focusing quality factor (FQF) as an indicator of how well the focusing is conducted with a given sound speed. The FQF is closely associated with the degree of edge conspicuity, which can be obtained using the proposed modified nonlinear anisotropic diffusion (MNAD) technique. To calculate FQF, ultrasound images are formed with different sound speeds ranging from 1400 to 1600 m/s and, subsequently, the ROI is chosen. In the ROI, the degrees of edge conspicuity (i.e., FQF) are calculated. The sound speed can be considered an optimal one for the ROI if it is used to construct the image that provides the maximum FQF. The performances of the proposed method were evaluated through simulation and in vitro experiments with a tissue-mimicking phantom. The performance was also compared with that of the conventional image-based method employed in a commercial ultrasound imaging system. The experimental results demonstrated that the proposed method is capable of estimating an optimal sound speed with an error of 10 m/s regardless of whether strong targets are included in the ROI or not. On the other hand, the conventional image-based method generated an estimation error of 60 m/s maximally in the case in which there were no strong targets in ROI. This indicates that the proposed method is a useful tool to improve ultrasound image quality for clinical applications, especially for ultrasound exams of obese patients and the breast.
在肥胖患者和乳房的超声检查中，当在接收动态波束形成中使用对应软组织的恒定声速时，超声图像的空间和对比分辨率会严重恶化。这种退化是由于软组织和脂肪层之间的声速差异导致超声束散焦所致。为了最大程度地减少这种退化，本文提出了一种新的估计最佳声速的方法，该方法可用于在感兴趣区域（ROI）中实现最佳的波束形成性能。所提出的方法采用了一种新的聚焦质量因子（FQF）作为指示符，用于指示使用给定声速进行聚焦的效果。FQF与边缘明显度密切相关，边缘明显度可以使用所提出的改进非线性各向异性扩散（MNAD）技术获得。为了计算 FQF，使用不同的声速（范围为 1400 至 1600 m/s）形成超声图像，然后选择 ROI。在 ROI 中，计算边缘明显度（即 FQF）的程度。如果使用它来构建提供最大 FQF 的图像，则可以认为该声速是 ROI 的最佳声速。通过模拟和使用组织模拟体模进行的体外实验评估了所提出方法的性能。还将该方法的性能与商用超声成像系统中使用的常规基于图像的方法进行了比较。实验结果表明，无论 ROI 中是否存在强目标，该方法都能够以 10 m/s 的误差估计最佳声速。另一方面，在 ROI 中没有强目标的情况下，常规基于图像的方法最大产生 60 m/s 的估计误差。这表明该方法是提高临床应用中超声图像质量的有用工具，特别是在肥胖患者和乳房的超声检查中。
