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

TL;DR

This paper explains the fundamentals of delay-and-sum (DAS) beamforming in ultrasound imaging, discusses how physical parameters affect image quality, and offers practical solutions for optimizing these parameters to improve imaging results.

Contribution

It provides a detailed theoretical and numerical analysis of DAS beamforming, highlighting the influence of the f-number and speed of sound, and proposes methods to set these parameters based on physical principles.

Findings

Improper setting of f-number and speed of sound degrades image quality.

Optimizing these parameters improves lateral resolution and contrast-to-noise ratio.

In vitro and in vivo experiments confirm the importance of parameter optimization.

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.