IEEE Trans Ultrason Ferroelectr Freq Control. 2022 Oct;69(10):2810-2822. doi: 10.1109/TUFFC.2022.3188245. Epub 2022 Sep 27.
Spiral array transducers with a sparse 2-D aperture have demonstrated their potential in realizing 3-D ultrasound imaging with reduced data rates. Nevertheless, their feasibility in high-volume-rate imaging based on unfocused transmissions has yet to be established. From a metrology standpoint, it is essential to characterize the acoustic field of unfocused transmissions from spiral arrays not only to assess their safety but also to identify the root cause of imaging irregularities due to the array's sparse aperture. Here, we present a field profile analysis of unfocused transmissions from a density-tapered spiral array transducer (256 hexagonal elements, 220- [Formula: see text] element diameter, and 1-cm aperture diameter) through both simulations and hydrophone measurements. We investigated plane- and diverging-wave transmissions (five-cycle, 7.5-MHz pulses) from 0° to 10° steering for their beam intensity characteristics and wavefront arrival time profiles. Unfocused firings were also tested for B-mode imaging performance (ten compounded angles, -5° to 5° span). The array was found to produce unfocused transmissions with a peak negative pressure of 93.9 kPa at 2 cm depth. All transmissions steered up to 5° were free of secondary lobes within 12 dB of the main beam peak intensity. All wavefront arrival time profiles were found to closely match the expected profiles with maximum root-mean-squared errors of [Formula: see text] for plane wave (PW) and [Formula: see text] for diverging wave. The B-mode images showed good spatial resolution with a penetration depth of 22 mm in PW imaging. Overall, these results demonstrate that the density-tapered spiral array can facilitate unfocused transmissions below regulatory limits (mechanical index: 0.034; spatial-peak, pulse-average intensity: 0.298 W/cm2) and with suppressed secondary lobes while maintaining smooth wavefronts.
螺旋阵列换能器具有稀疏的二维孔径，已证明其在降低数据速率的情况下实现 3D 超声成像的潜力。然而，它们在基于非聚焦发射的高容量成像中的可行性尚未得到证实。从计量学的角度来看，对非聚焦传输的螺旋阵列声场进行特征描述是至关重要的，这不仅是为了评估其安全性，也是为了确定由于阵列稀疏孔径导致成像不规则的根本原因。在这里，我们通过模拟和水听器测量，对密度渐变螺旋阵列换能器（256 个六边形单元，[Formula: see text]单元直径，1cm 孔径直径）的非聚焦传输进行了场分布分析。我们研究了平面波和发散波传输（五个周期，7.5MHz 脉冲），从 0°到 10°转向，以研究其波束强度特性和波前到达时间分布。还对非聚焦发射进行了 B 模式成像性能测试（十个复合角度，-5°到 5°范围）。结果发现，该阵列在 2cm 深度处产生的非聚焦传输的峰值负压为 93.9kPa。所有转向至 5°的传输在主波束峰值强度 12dB 以内都没有二次瓣。所有波前到达时间分布都与预期分布非常吻合，平面波（PW）的最大均方根误差为[Formula: see text]，发散波为[Formula: see text]。PW 成像的 B 模式图像具有良好的空间分辨率，穿透深度为 22mm。总的来说，这些结果表明，密度渐变螺旋阵列可以在低于监管限制（机械指数：0.034；空间峰值、脉冲平均强度：0.298W/cm2）的情况下实现非聚焦传输，并抑制二次瓣，同时保持波前平滑。
