So you think you can DAS? A viewpoint on delay-and-sum beamforming

Vincent Perrot; Maxime Polichetti; François Varray; Damien Garcia

doi:10.1016/j.ultras.2020.106309

So you think you can DAS? A viewpoint on delay-and-sum beamforming

Ultrasonics. 2021 Mar:111:106309. doi: 10.1016/j.ultras.2020.106309. Epub 2020 Dec 14.

Authors

Vincent Perrot¹, Maxime Polichetti¹, François Varray¹, Damien Garcia²

Affiliations

¹ CREATIS, CNRS UMR 5220, INSERM U1206, Université Lyon 1, INSA Lyon, France.
² CREATIS, CNRS UMR 5220, INSERM U1206, Université Lyon 1, INSA Lyon, France. Electronic address: damien.garcia@inserm.fr.

PMID: 33360053
DOI: 10.1016/j.ultras.2020.106309

Abstract

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.

Keywords: Beamforming; Delay-and-sum; Speed of sound; f-number.