Large-Pitch Synthetic Transmit Aperture Imaging: A Feasibility Study

Abstract

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 MB-STA 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.

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

“…The SRF was proposed to use for the PTPR method with the transmit and receive pre-steering angle equals to zero (i.e. [17]. The SRF had an analytical expression (Eq.…”

“…In this article, we use the SRF for the MB-STA method to improve the contrast outside the focal region. Thus, the image reconstruction is shown as [17],…”

“…The L and K were chosen to be prime to each other (no common factor), therefore, the directivity of the transmit and receiving SAPs were used to suppress the grating lobe artifacts and thus maintain a reasonable imaging quality. In [17], we proposed to use the LPSTA with planar transmission and planar receiving (PTPR), we refer it as PTPR method in this article. It means all the transmission SAPs are steered in parallel to the same direction and the receiving SAPs are also steered to the same angle as in the transmission.…”

“…Therefore, we propose to use spatial response function (SRF) in the reconstruction process of the MB-STA method to partially compensate for the contrast loss of the targets located at the out-of-focal regions, especially for the near-field targets. The SRF introduced in [17] had an analytical expression based on the far-field approximation.…”

“…In Section II, the theory of LPSTA method [17] is first briefly reviewed. The focused transmission and receiving processes, the spatial response function and its implementation, and the beam pattern for FOV analysis were introduced.…”