A Frequency-Domain Plane-Wave Ultrasound Imaging Method with Amplitude-Normalized Coherence Weighting

Frequency-domain plane-wave imaging (FPWI) enables ultrafast frame rates for ultrasonic nondestructive evaluation. However, image quality can still be degraded by noise and artifacts. Most coherence-weighting schemes are implemented in the time domain using sliding-window statistics, which introduce substantial computation and memory-access overhead. In this work, we compute coherence weights directly in the frequency domain using the fast Fourier transform (FFT). Inspired by spatial coherence principles related to the van Cittert–Zernike theorem (VCZ), we propose a normalized amplitude coherence factor (NACF) as an amplitude-domain alternative to the normalized energy coherence factor (NECF). Experiments on representative defect datasets show that FPWI with NACF improves contrast ratio (CR), signal-to-noise ratio (SNR), and array performance indicator (API) relative to baseline FPWI, while further sharpening defect boundaries and enhancing lateral resolution. These results demonstrate a favorable balance between artifact suppression and resolution enhancement, making the proposed method a promising solution for ultrasonic NDE scenarios requiring both high frame rates and high imaging quality.