Array Smoothing Coherence Factor in the Plane-Wave Ultrasound Imaging

The coherence factor (CF) and generalized coherence factor (GCF) have been proposed as effective methods to suppress the output noise and distortion of the traditional delay and sum (DAS) beamformer in the ultrasound imaging. However, previous researches use all transducer elements for analysis and calculation in the plane-wave ultrasound imaging (PWUI). The larger phase aberration caused by the larger size of receiving aperture results in some negative effects such as the over-suppression of speckle backgrounds and excessive attenuation on depth distribution. In this paper, an array smoothing method is proposed to optimize the conventional CF and GCF weighting processes. The idea of this method is to transform one-dimensional signal vectors to two-dimensional signal matrices by array smoothing so as to reduce the length of the signal arrays. The angle threshold is set to determine the effective receiving aperture. Then the CF and GCF weights are optimized and finally multiplied with the DAS output. Simulated and experimental studies are both analyzed to evaluate the performance of the array smoothing coherence factor (ASCF) and generalized coherence factor (ASGCF) methods. Results show that the ASCF and ASGCF methods obtained both higher contrast ratio and contrast-to-noise ratio over conventional CF and GCF methods in both simulated and experimental studies. Furthermore, it shows a better performance on reducing the distortion of speckle backgrounds and improving the robustness on the depth distribution. Therefore, the proposed methods benefit a higher speckle signal-to-noise ratio. Although it suffers a slight resolution loss, the ASCF and ASGCF methods proposed in this paper are effective in enhancing image qualities in the PWUI.