Transmit Beam Pattern (TBP) optimization is an important task in medical ultrasound especially in some advanced applications like continuous wave Doppler or shear wave generation in acoustic radiation force impulse elastography. Standard TBP is based on transmission focused at a fixed focal depth: this results in 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, in this work we present a novel optimization approach for TBP by focusing the analysis on the narrow band approximation of the TBP 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. The narrow band case leads naturally to reformulate the problem in the frequency domain, with a significant computational saving with respect to time domain. The optimized narrowband beam patterns have been compared with a large set of standard ones, showing an overall improvement of desired features, thus demonstrating the effectiveness of the proposed approach. Moreover, in order to allow a quantitative evaluation of the improvement, a novel set of metrics is introduced.
翻译:在超声波连续波波多普勒或剪裁波生成等先进应用中,在声波辐射力脉冲脉冲脉动中,标准TBP优化是医学超声波的一项重要任务。标准TBP基于以固定焦点深度为焦点的传输:这导致了众所周知的缺陷,如非统一光束宽度超过深度、存在重要的侧边叶和在焦点深度后快速能量下降。为了克服这些限制,我们在此工作中为TBP提出了一个新的优化方法,将分析重点放在TBP的窄带近距离上,并考虑将延迟作为自由变量传送,而不是作为与特定的焦深度连接。我们将这一问题发展成一个非线性的最低方块问题,以尽量减少TBPP与一系列延迟和理想的2D矩形形之间的差别。窄带案自然导致重塑频率区域的问题,同时在时间域方面大量进行计算节约。最佳的窄带模式与一套大型标准方块相比,我们把问题发展成非线性最低方块方块,以尽量缩小方块为一组,从而显示预期的量化方法的改进。