Ultrasound Baseband Delay-Multiply-and-Sum (BB-DMAS) nonlinear beamforming

Che-Chou Shen; Pei-Ying Hsieh

doi:10.1016/j.ultras.2019.01.010

Ultrasound Baseband Delay-Multiply-and-Sum (BB-DMAS) nonlinear beamforming

Ultrasonics. 2019 Jul:96:165-174. doi: 10.1016/j.ultras.2019.01.010. Epub 2019 Jan 31.

Authors

Che-Chou Shen¹, Pei-Ying Hsieh²

Affiliations

¹ Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan. Electronic address: choushen@mail.ntust.edu.tw.
² Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.

PMID: 30765204
DOI: 10.1016/j.ultras.2019.01.010

Abstract

Compared to conventional Delay-and-Sum (DAS) beamforming, Delay-Multiply-and-Sum (DMAS) imaging uses multiplicative coupling of channel pairs for spatial coherence of receiving aperture to improve image resolution and contrast. However, present DMAS imaging is based on the radio-frequency (RF) channel signals (RF-DMAS) and thus requires large oversampling to avoid aliasing and switching of band-pass filtering to isolate the corresponding spectral components for imaging. Baseband DMAS (BB-DMAS) beamforming in this study is based on the demodulated channel signals to provide similar results but with simplified signal processing. The BB-DMAS beamforming scales the magnitude of time-delayed channel signal by p-th root while maintaining the phase. After channel sum, the output dimensionality is restored by p-th power. The multiplicative coupling in BB-DMAS always renders baseband signal and thus the need for oversampling is eliminated. Besides, the BB-DMAS can use any rational p values to provide flexible image quality and an explicit relation between BB-DMAS beamforming and channel-domain phase coherence exists. Our results show that the image characteristics between BB-DMAS and RF-DMAS are similar. The suppression of lateral side lobe level, grating lobe level and uncorrelated random noises gradually increases with the rational p value in BB-DMAS beamforming. The image contrast improves from -24.8 dB in DAS to -34.3 dB, -43.0 dB and -51.4 dB in BB-DMAS, respectively with p value of 1.5, 2.0 and 2.5. In conclusion, BB-DMAS beamforming provides flexible manipulation of image quality by introducing baseband spatial coherence in the ultrasonic imaging.

Keywords: Adaptive imaging; Baseband beamforming; Delay-Multiply-and-Sum (DMAS); Spatial coherence.