Weighted Capon beamformer combined with coded excitation in ultrasound imaging

Abstract

Background: Capon-based beamformers are well-known methods to improve the SNR and quality of medical ultrasound images. Furthermore, they can improve the resolution of the images unexpectedly more than conventional DAS beamformers. Another method used in radar, sonar, and ultrasound imaging to increase the SNR is coded excitation with linear frequency-modulated signal (chirp).

Method: In this paper, we illustrate that the combination of coded excitation with a Capon beamformer provides better resolution and higher SNR. However, this combination suffers from high sidelobe levels. We propose a weighted Capon beamformer (WCB) with chirp excitation to suppress the sidelobes and obtain a higher contrast with approximately the same resolution as the standard Capon beamformer (SCB). The weights of the WCB are obtained using element-wise multiplication of the weights of the SCB and a desired window (Hanning) with the same dimension.

Results: The results show a 20 dB reduction in the sidelobe levels in simulated point targets and a 6 dB increase in background contrast in simulated cyst phantoms.

Keywords: Adaptive beamformer; Capon; Chirp; Coded excitation; Minimum variance.