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Abstract
Ultrasonic multi-angle plane-wave (PW) coherent compounding relies on delay-and-sum (DAS) beamforming of two-dimensional (2D) echo matrix in both the dimensions PW transmit angle and receiving channel to construct each image pixel. Due to the characteristics of DAS beamforming, PW coherent compounding may suffer from high image clutter when the number of transmit angles is kept low for ultrafast image acquisition. Delay-multiply-and-sum (DMAS) beamforming exploits the spatial coherence of the receiving aperture to suppress clutter interference. Previous attempts to introduce DMAS beamforming into multi-angle PW imaging has been reported but only in either dimension of the 2D echo matrix. In this study, a novel DMAS operation is proposed to extract the 2D spatial coherence of echo matrix for further improvement of image quality. The proposed 2D-DMAS method relies on a flexibly tunable p value to manipulate the signal coherence in the beamforming output. For p = 2.0 as an example, simulation results indicate that 2D-DMAS outperforms other one-dimensional DMAS methods by at least 9.3 dB in terms of ghost-artifact suppression. Experimental results also show that 2D-DMAS provides the highest improvement in lateral resolution by 32% and in image contrast by 15.6 dB relative to conventional 2D-DAS beamforming. Nonetheless, since 2D-DMAS emphasizes signal coherence more than its one-dimensional DMAS counterparts, it suffers from the most elevated speckle variation and the granular pattern in the tissue background.
Highlights
In medical ultrasound imaging, delay-and-sum (DAS) beamforming is the standard technique to produce image outputs
We have previously developed an alternative high-order baseband DMAS beamforming (BB-DMAS) [21] to avoid the aforementioned oversampling because the multiplication of baseband channel data does not lead to undesired spectral components at high frequencies
Simulated B-mode images of wire reflectors in Figure 1a–d show that the 2D-DMAS, Rx-DMAS, and Tx-DMAS beamforming methods can effectively suppress side-lobe and ghost artifact compared to conventional coherent plane wave compounding (CPWC) imaging (i.e., 2D-DAS)
Summary
Delay-and-sum (DAS) beamforming is the standard technique to produce image outputs. In PW imaging, an unfocused wave is transmitted to illuminate a wide field-of-view, and the backscattered echoes in the receiving array are coherently summed after time compensation of geometric paths to generate low-quality images at frame rates on the order of kHz. To improve the image quality of PW imaging, coherent plane wave compounding (CPWC) uses multi-angle PW transmissions to achieve synthetic transmit focusing [2,3]. Unlike incoherent compounding, which combines the envelope image without phase information to reduce speckle variation, CPWC depends on the summation of image data with phase information to achieve synthetic focusing. Low-quality images are firstly obtained with different PW transmit angles and combined coherently to form the final high-quality image
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