Coherent Plane-Wave Compounding Based on Normalized Autocorrelation Factor

Coherent plane-wave compounding (CPWC) is an effective method to improve the image quality of ultrasound plane-wave imaging (PWI), which coherently sums the delay-and-sum (DAS) beamforming outputs of PWI at different steering angles. However, due to the data-independent nature, the DAS obtains limited imaging resolution and contrast. Therefore, various adaptive beamforming methods have been presented to achieve improved imaging quality. In this paper, an adaptive weighting factor named normalized autocorrelation factor (NAF), which is derived by the normalized autocorrelation function (NACF), is proposed for CPWC. Simulated and experimental data provided by the plane wave imaging challenge in medical ultrasound organizers are used to evaluate the proposed method. Results show that the NAF-weighted CPWC can achieve an improved imaging quality in terms of lateral resolution, contrast ratio (CR), and contrast-to-noise ratio. In simulated images, the maximum improvements of the lateral full width at half maximum and CR are 60.3% and 29.7%, respectively. For experimental images, the corresponding improvements are 32.1% and 23.3%. The NAF is also compared with the generalized coherence factor (GCF) and short-lag spatial coherence (SLSC), and the simulation and phantom experimental results show that the NAF can get better lateral resolution and speckle signal-to-noise ratio (sSNR). For in-vivo data, the NAF shows distinct advantages over GCF and SLSC in preserving anatomical structures so as to get better CR, CNR, and sSNR. In addition, with a low computational complexity and load, the proposed method has potential to be applied to ultrafast ultrasound imaging for high quality images.