Angular-first channel-domain delay-multiply-and-sum beamforming with dual coherence for row-column array-based 3D power Doppler imaging.

Row-column arrays (RCAs) enable large-aperture ultrafast three-dimensional (3D) ultrasound imaging using two orthogonal sets of N elongated elements, reducing the channel count from N2 for an N × N fully addressed matrix array to 2N. However, the elongated elements spatially mix echoes along their long axes, while the orthogonal transmit-receive geometry produces pronounced cross-shaped artifacts, particularly with limited transmit angles. We propose two RCA-specific beamformers: delay-multiply-and-sum with a channel coherence factor (DMAS-CCF), applied to angle-compounded channel signals, and its extension incorporating an aperture cross-coherence factor (DMAS-CCF-ACF). The proposed beamformers were compared with orthogonal plane wave (OPW) compounding, XDoppler, and row-column-specific frame-multiply-and-sum (RC-FMAS) using point-target and microtube simulations and in vivo rat testicular and renal experiments under 32 + 32 and 8 + 8 transmit-angle configurations. Compared with OPW, DMAS-CCF and DMAS-CCF-ACF reduced the full width at half maximum (FWHM) from 0.410 mm to 0.220 mm and 0.206 mm, respectively, under the 32 + 32 transmit-angle configuration. DMAS-CCF-ACF also yielded the lowest sidelobe levels (SLLs). The proposed beamformers achieved smaller minimum separable distances than the comparison beamformers in microtube simulations. In vivo, DMAS-CCF-ACF yielded the highest contrast-to-noise ratio (CNR) in both organs under both configurations. Under the 8 + 8 transmit-angle configuration, the testicular CNR was 29.81 dB for DMAS-CCF-ACF, compared with 9.66 dB for OPW, 12.08 dB for XDoppler, and 12.02 dB for RC-FMAS. These findings indicate that the proposed beamformers improve spatial resolution and reduce RCA-specific artifacts, enabling more faithful delineation of 3D vascular architecture.