Ultrasound imaging is extensively employed in clinical settings due to its non-ionizing nature and real-time capabilities. The beamformer represents a crucial component of an ultrasound machine, playing a significant role in shaping the ultimate quality of the reconstructed image. Therefore, Transmit Beam Pattern (TBP) optimization is an important task in medical ultrasound, but state-of-the-art TBP optimization has well-known drawbacks like non-uniform beam width over depth, presence of significant side lobes, and quick energy drop out after the focal depth. To overcome these limitations, we developed a novel optimization approach for TBP by focusing the analysis on its narrowband approximation, particularly suited for Acoustic Radiation Force Impulse (ARFI) elastography, and considering transmit delays as free variables instead of linked to a specific focal depth. We formulate the problem as a non linear Least Squares problem to minimize the difference between the TBP corresponding to a set of delays and the desired one, modeled as a 2D rectangular shape elongated in the direction of the beam axis. In order to quantitatively evaluate the results, we define three quality metrics based on main lobe width, side lobe level, and central line power. Results obtained by our synthetic software simulation show that the main lobe width is considerably more intense and uniform over the whole depth range with respect to classical focalized Beam Patterns, and our optimized delay profile results in a combination of standard delay profiles at different focal depths. The application of the proposed method to ARFI elastography shows improvements in the concentration of the ultrasound energy along a desired axis.

翻译：超声成像因其非电离特性和实时能力而广泛应用于临床。波束形成器作为超声设备的关键组件，对重建图像的最终质量起着重要作用。因此，传输波束模式优化是医学超声领域的重要任务，但现有最先进的传输波束模式优化方法存在明显缺陷，如波束宽度随深度变化不均匀、显著旁瓣存在以及聚焦深度后能量快速衰减。为解决这些局限，我们开发了一种新的传输波束模式优化方法，通过聚焦其窄带近似分析（特别适用于声辐射力脉冲弹性成像），并将传输延时视为自由变量而非与特定聚焦深度关联。我们将问题表述为非线性最小二乘问题，以最小化对应一组延时的传输波束模式与期望模式（建模为沿波束轴方向延伸的二维矩形形态）之间的差异。为定量评估结果，我们定义了基于主瓣宽度、旁瓣电平和中心线功率的三个质量指标。合成软件仿真结果表明，与经典聚焦波束模式相比，主瓣宽度在整个深度范围内显著增强且更均匀，优化后的延时分布表现为不同聚焦深度标准延时分布的融合组合。将该方法应用于声辐射力脉冲弹性成像，可改善超声能量沿目标轴线的集中度。