Recent Developments in Adaptive Beamforming

Beamforming is an indispensable process to obtain an ultrasound image. In most of clinical ultrasound systems, the delay-and-sum (DAS) beamformer is implemented. The DAS beamformer applies time delays to ultrasonic echo signals received by individual transducer elements in an ultrasonic probe so that the phases of echoes from a point at the focus are aligned and, then, the delay compensated signals are summed to enhance the echo signal from the focal point. The DAS beamformer is very computationally efficient and suitable for real-time processing. On the other hand, its ability in suppression of off-axis signals is limited. To improve the performance of ultrasound beamformers, various studies on adaptive beamformers have been conducted for a long time and still being continuing nowadays. This paper provides a brief review on adaptive beamformers, particularly on the coherence-based adaptive imaging and its relation to the minimum variance beamforming.