CREATIS, CNRS UMR 5220, INSERM U1206, Université Lyon 1, INSA Lyon, France.
CREATIS, CNRS UMR 5220, INSERM U1206, Université Lyon 1, INSA Lyon, France.
Ultrasonics. 2021 Mar;111:106309. doi: 10.1016/j.ultras.2020.106309. Epub 2020 Dec 14.
Delay-and-sum (DAS) is the most widespread digital beamformer in high-frame-rate ultrasound imaging. Its implementation is simple and compatible with real-time applications. In this viewpoint article, we describe the fundamentals of DAS beamforming. The underlying theory and numerical approach are detailed so that users can be aware of its functioning and limitations. In particular, we discuss the importance of the f-number and speed of sound on image quality, and propose one solution to set their values from a physical viewpoint. We suggest determining the f-number from the directivity of the transducer elements and the speed of sound from the phase dispersion of the delayed signals. Simplified Matlab codes are provided for the sake of clarity and openness. The effect of the f-number and speed of sound on the lateral resolution and contrast-to-noise ratio was investigated in vitro and in vivo. If not properly preset, these two factors had a substantial negative impact on standard metrics of image quality (namely CNR and FWHM). When beamforming with DAS in vitro or in vivo, it is recommended to optimize these parameters in order to use it wisely and prevent image degradation.
延迟求和（DAS）是在高帧率超声成像中应用最广泛的数字波束形成器。它的实现简单，与实时应用程序兼容。在这篇观点文章中，我们描述了 DAS 波束形成的基本原理。详细介绍了其理论基础和数值方法，以便用户了解其功能和局限性。特别是，我们讨论了 f-number 和声速对图像质量的重要性，并提出了一种从物理角度设置其值的解决方案。我们建议从换能器元件的指向性确定 f-number，从延迟信号的相位色散确定声速。为了清晰和开放，提供了简化的 Matlab 代码。在体外和体内研究了 f-number 和声速对横向分辨率和对比噪声比的影响。如果不正确预设，这两个因素会对图像质量的标准指标（即 CNR 和 FWHM）产生实质性的负面影响。在体外或体内使用 DAS 进行波束形成时，建议优化这些参数，以明智地使用它并防止图像降级。
