SCORE beamforming: Spectral COherence REfinement for high-contrast ultrafast Doppler imaging

Delay-and-sum (DAS) beamforming is widely used in ultrasound flow imaging due to its computational simplicity; however, its high sidelobe levels significantly degrade image contrast. Coherence factor (CF) beamforming partially alleviates this limitation by emphasizing spatial coherence, yet residual incoherent energy remains and continues to impair image quality. In this study, we propose a dual-stage beamforming approach that integrates CF weighting with a frequency-domain filtering stage designed to discriminate and suppress incoherent energy while preserving coherent signal components. The proposed method, termed SCORE (Spectral COherence REfinement), introduces an additional coherence-based discrimination mechanism beyond conventional CF beamforming. Simulation experiments involving single-target, multi-target, and vascular scenarios demonstrate that SCORE achieves substantial sidelobe suppression while maintaining signal integrity. In vivo validation using an open-source contrast-enhanced rat brain and kidney dataset, as well as contrast-free human spleen further confirms improved flow detectability, reduced background noise, and enhanced power Doppler imaging performance, as evidenced by increases in SNR and CNR approaching 10 dB compared to CF and GCF beamforming. Overall, the SCORE beamformer provides a robust framework for high-contrast vascular ultrasound imaging, offering superior sidelobe and noise suppression relative to DAS, CF and GCF. To enhance computational efficiency, the beamforming pipeline was implemented on a graphics processing unit (GPU) using an optimized CUDA framework, achieving real-time beamforming performance with processing times below 30 ms per frame.