Coherence from REFoCUS compared to Retrospective Transmit Beamforming

Synthetic transmit focusing are techniques that synthesizes transmit focus retrospetively in the recorded channel data from multiple transmissions. Synthetic transmit focusing has a large impact on the estimated coherence in medical ultrasound imaging, since the coherence is dependent on the type of transmitted wave and, for focused transmissions, the location of the focus. Retrospective Transmit Beamforming (RTB) is currently the state-of-the-art for focused transmit b-mode imaging in clinical scanners. An alternative approach for synthetic transmit focusing, REFoCUS (Retrospective Encoding For Conventional Ultrasound Sequences) can reconstruct the full synthetic transmit aperture imaging dataset. We compare the resulting b-mode images and coherence obtained from RTB, REFoCUS and conventional scanline beamforming and demonstrate that REFoCUS and RTB have comparable results. However, REFoCUS has slight improvements in terms of contrast, resolution and coherence compared to RTB as well as the main advantage of REFoCUS; that it is less dependent on the fine tuning of delay models and apodization needed for RTB. Thus, REFoCUS is a powerful tool for software beamforming.