Coherent multi-transducer ultrasound imaging using diverging waves

Medical ultrasound imaging with large field of view (FoV) and high resolution remains a challenge due to the physical limitations of conventional apertures. Coherent multi-transducer ultrasound (CoMTUS) imaging addresses this by coherently combining data from multiple arrays to create a larger effective aperture, improving imaging performance. Accurate calibration of array positions is essential for coherent compounding, requiring sufficient overlap between insonified regions. However, existing CoMTUS implementations using plane waves (PWs) suffer from narrow, depth-dependent overlap of FoV, making calibration challenging and restricting performance. In this work, CoMTUS is extended to diverging wave (DW) imaging to increase FoV and improve calibration robustness. A novel multi-transmission calibration method is proposed to address the reduced coherence of DW echoes. By enabling inter-probe calibration directly from the DW imaging sequence, the proposed framework represents a key step toward future real-time, online CoMTUS calibration. The method was validated through simulations and experiments using two phased arrays imaging tissue-mimicking phantoms and the human abdominal aorta in vivo. Results demonstrate that CoMTUS with DWs enables extended FoV imaging with calibration errors consistently below the diffraction limit, while retaining improved resolution, contrast, and detectability previously demonstrated with PWs. For this two-probe configuration, an optimal divergence angle (β∼60°) and corresponding maximum steering angle (α_max∼32°) were identified, balancing FoV coverage and avoiding direct transmissions between arrays, showing improvements in peak side-to-main lobe ratio up to 4 dB. Increasing the number of DWs improved contrast (gCNR improving from 0.60 to 0.99 in simulations, and 0.50 to 0.65 in vivo), with diminishing returns beyond 11 transmissions. This approach holds potential for advancing ultrasound imaging in clinical applications requiring large coverage and precise anatomical visualization.