IEEE Trans Ultrason Ferroelectr Freq Control. 2020 Jul;67(7):1317-1331. doi: 10.1109/TUFFC.2020.2971238. Epub 2020 Feb 3.
A 3-D or large-aperture 2-D synthetic transmit aperture (STA) ultrasound imaging system with a fully sampled array usually leads to high hardware complexity and cost since each element in the array is individually controlled. To reduce the hardware complexity, we propose a large-pitch method for STA (LPSTA) imaging integrated with a spatial response function (SRF) in the image reconstruction to improve image quality. To achieve this, we decreased the total number of measurement channels M (the product of the number of transmissions I and the number of the receive channels in each transmission I ). We combined L adjacent elements in transmission and K adjacent elements in receive into subapertures (SAPs), where L and K were coprime (no common factors) integers to suppress the grating lobes. We denoted it as an ( N/L, N /K ) system, where N is the number of transducer elements. In this article, first, we derived the beam pattern of the LPSTA using a far-field approximation. We demonstrated that the coprime selection and SRF can significantly reduce the grating lobes level (GLL) by using a beam pattern analysis. We also found that the LPSTA can have a similar beam pattern as that of a full array when the target is located along the steering direction. Second, the imaging performance of LPSTA was evaluated and validated with Field II simulations and experiments. The simulation results demonstrated that the proposed LPSTA with ( N /3, N /5) can achieve on average ~25% improvement in lateral resolution, ~24.6% and ~42.3% improvement in contrast-to-noise ratio (CNR) and contrast ratio (CR), respectively, over B-mode with a large-pitch receiver with ( N , N /5). LPSTA achieved comparable image contrast to the standard STA with the full array ( N , N ) at the cost of a reduced field of view. The experiment results were consistent with the simulation results. Finally, in addition to reducing the system (hardware) complexity, the LPSTA was more computationally efficient than the standard STA with a full array. The proposed method may help in realizing clinical applications of real-time 2-D or 3-D ultrasound imaging using large arrays.
一种具有完全采样阵列的三维或大孔径二维合成发射孔径（STA）超声成像系统通常会导致硬件复杂性和成本增加，因为阵列中的每个元件都需要单独控制。为了降低硬件复杂性，我们提出了一种与图像重建中的空间响应函数（SRF）集成的大间距 STA（LPSTA）成像方法，以提高图像质量。为了实现这一点，我们减少了总测量通道数 M（发射次数 I 与每次发射中接收通道数 I 的乘积）。我们将发射中的 L 个相邻元件和接收中的 K 个相邻元件组合成子孔径（SAP），其中 L 和 K 是互质（没有公共因子）的整数，以抑制栅瓣。我们将其表示为（ N/L ， N /K ）系统，其中 N 是换能器元件的数量。在本文中，首先，我们使用远场近似法推导出 LPSTA 的波束图案。我们通过波束图案分析表明，互质选择和 SRF 可以显著降低栅瓣电平（GLL）。我们还发现，当目标位于转向方向时，LPSTA 可以具有与全阵列相似的波束图案。其次，我们使用 Field II 模拟和实验评估和验证了 LPSTA 的成像性能。模拟结果表明，与具有大间距接收器的 B 模式相比，采用（ N /3 ， N /5）的所提出的 LPSTA 可以在横向分辨率上平均提高约 25%，在对比度噪声比（CNR）和对比度（CR）上分别提高约 24.6%和 42.3%。LPSTA 在降低视场的情况下，实现了与具有全阵列（ N ， N ）的标准 STA 相当的图像对比度。实验结果与模拟结果一致。最后，除了降低系统（硬件）复杂性外，LPSTA 比具有全阵列（ N ， N ）的标准 STA 具有更高的计算效率。该方法可能有助于实现使用大阵列的实时二维或三维超声成像的临床应用。
