Specific Filtered Delay Multiply and Sum beamforming for coherent multi-transducer ultrasound imaging

Coherent multi-transducer ultrasound (CoMTUS) imaging enables the use of multiple arrays as one large effective aperture yielding images with enlarged field-of-view, improved resolution, and higher signal-to-noise ratio. However, creating a large but discontinuous effective aperture increases the grating and sidelobe levels, and generates cross-talk artifacts between arrays. These additional challenges can degrade the contrast of the images obtained through the classic Delay and Sum (DAS) beamforming algorithm. This study investigates the possibility to improve contrast and reduce artifacts in CoMTUS by using an alternative nonlinear beamforming algorithm, the Filtered Delay Multiply and Sum (F-DMAS). We implemented a specific F-DMAS beamforming algorithm for CoMTUS considering the resulting effective aperture and tested its performance in a coherent dual-array system for 2-D imaging. The comparison between CoMTUS images obtained through F-DMAS and DAS was investigated by both simulations and experiments, including in vivo results. For a typical dual-probe configuration, CoMTUS specific F-DMAS was shown to be effective at lowering the sidelobes and the noise floor, resulting in better quality B-mode images with improved sidelobe suppression (first sidelobe amplitude decreased from -13.0 dB to -24.7 dB; side-lobe-to-main-lobe energy ratio decreased from 9.3 dB to 1.9 dB).