Short-lag spatial coherence imaging using minimum variance beamforming on dual apertures

Abstract

Background: Short-lag spatial coherence (SLSC) imaging, a newly proposed ultrasound imaging scheme, can offer a higher lesion detectability than conventional B-mode imaging. It requires a high focusing quality which can be satisfied by the synthetic aperture imaging mode. However, traditional nonadaptive synthesis for the SLSC still offers an unsatisfactory resolution. The spatial coherence estimation on the receive aperture cannot fully utilize the coherence information in two-dimensional (2D) echo data.

Methods: To overcome these drawbacks, an improved SLSC scheme with adaptive synthesis on dual apertures is proposed in this paper. The minimum variance (MV) beamformer is applied in synthesizing both the receiving and transmitting apertures, while the SLSC function is estimated on both apertures as well. In this way, the resolution is enhanced by the MV implementation, while the coherence in dual apertures is fully utilized.

Results: Simulations, phantom experiments, and in vivo studies are conducted to evaluate the performance of the proposed method. Results demonstrate that the proposed method achieves the best performance in terms of the contrast ratio (CR), contrast-to-noise ratio (CNR), and the speckle signal-to-noise ratio (SNR). Specifically, compared with the delay-and-sum (DAS) method, the proposed method achieves 42.5% higher CR, 412.7% higher CNR, and 402.9% higher speckle SNR in simulations. The resolution is also better than the DAS and conventional SLSC beamformers.

Conclusions: The proposed method is a promising technique for improving the SLSC imaging quality and can provide better visualization for medical diagnosis.

Keywords: Adaptive beamforming; Minimum variance; Short-lag spatial coherence; Synthetic aperture; Ultrasound imaging.

Fig. 1

Simulated point scatterers: a DAS, b MV, c SLSC, d DA-MV SLSC. The a and b are B-mode images shown with a dynamic range of 60 dB

Fig. 2

Lateral variations of different beamformed responses at a z = 30 mm, b z = 35 mm, c z = 40 mm, d z = 45 mm in the point target simulation

Fig. 3

Simulated anechoic cysts: a DAS, b MV, c SLSC, d DA-MV SLSC. The a and b are B-mode images shown with a dynamic range of 60 dB

Fig. 4

Experimental wire target phantom: a DAS, b MV, c SLSC, d DA-MV SLSC. The a and b are B-mode images shown with a dynamic range of 60 dB

Fig. 5

Lateral variations of different beamformed responses at a z = 19 mm, b z = 28 mm in the wire target phantom experiment

Fig. 6

Experimental anechoic cyst: a DAS, b MV, c SLSC, d DA-MV SLSC. The a and b are B-mode images shown with a dynamic range of 60 dB

Fig. 7

In vivo human carotid artery: a DAS, b MV, c SLSC, d DA-MV SLSC. The a and b are B-mode images shown with a dynamic range of 60 dB