Large-pitch Synthetic Transmit Aperture Imaging with micro-beamforming technique

We propose to combine synthetic transmit aperture imaging with the micro-beamforming technique (MB-STA) to improve the image quality of the large-pitch synthetic transmit aperture imaging (LPSTA). In LPSTA, nearby array elements are combined as sub-aperture (SAP) without pre-steering delays in both transmit and receive to reduce hardware complexity. In MB-STA , pre-steering delays or microbeamforming within the transmit and receive sub-aperture is introduced to steer the transmission and receiving beams to a focal point. Focusing for the points away from the focal point is then achieved through the image reconstruction using the micro-beamformed RF data in synthetic transmit aperture imaging. Spatial response functions (SRF) are applied in the image reconstruction to compensate for the contrast loss, especially when the targets are located outside the focal region. The simulation results demonstrated that MB-STA can attain an image quality comparable to the standard STA of a fullyindexed array, but with a 66-fold reduction in the number of measurement channels, at the cost of a smaller field of view. Moreover, our experimental results demonstrated that for targets located outside of the focal region, the proposed MBSTA method has better image quality than that of the conventional B-mode imaging with a similar microbeamforming configuration. The proposed method can be extended to 3D ultrasound imaging to reduce its excessive hardware complexity and cost.