Li Meng-Lin, Guan Wei-Jung, Li Pai-Chi
National Taiwan University, Department of Electrical Engineering, Taipei, Taiwan.
IEEE Trans Ultrason Ferroelectr Freq Control. 2004 Jan;51(1):63-70. doi: 10.1109/tuffc.2004.1268468.
Synthetic aperture focusing using a virtual source was used previously to increase the penetration and to extend the depth of focus in high-frequency ultrasonic imaging. However, the performance of synthetic aperture focusing is limited by its high sidelobes. In this paper, an adaptive weighting technique based on a focusing-quality index is introduced to suppress the sidelobes. The focusing-quality index is derived from the spatial spectrum of the scan-line data along the mechanical scan direction (i.e., the synthetic aperture direction) after focusing delays relative to the virtual source have been applied. The proposed technique is of particular value in high-frequency ultrasound in which dynamic focusing using array transducers is not yet possible. Experimental ultrasound data from a 50-MHz imaging system with a single-crystal transducer (f-number = 2) are used to demonstrate the efficacy of the proposed technique on both wire targets and speckle-generating objects. An in vivo experiment also is performed on a mouse to further demonstrate the effectiveness. Both 50-MHz fundamental imaging and 50-MHz tissue harmonic imaging are tested. The results clearly demonstrate the effectiveness in sidelobe reduction and background-noise suppression for both imaging modes. The principles, experimental results, and implementation issues of the new technique are described in this paper.
此前曾使用基于虚拟源的合成孔径聚焦来提高高频超声成像中的穿透深度并扩展焦深。然而，合成孔径聚焦的性能受到其高旁瓣的限制。本文介绍了一种基于聚焦质量指标的自适应加权技术来抑制旁瓣。聚焦质量指标是从沿机械扫描方向（即合成孔径方向）的扫描线数据的空间谱中得出的，该空间谱是在应用了相对于虚拟源的聚焦延迟之后得到的。所提出的技术在高频超声中具有特殊价值，因为在高频超声中使用阵列换能器进行动态聚焦尚不可能。来自具有单晶换能器（f数 = 2）的50兆赫成像系统的实验超声数据用于证明所提出的技术对线状目标和散斑产生物体的有效性。还对一只小鼠进行了体内实验以进一步证明其有效性。对50兆赫基波成像和50兆赫组织谐波成像都进行了测试。结果清楚地证明了该新技术在两种成像模式下降低旁瓣和抑制背景噪声方面的有效性。本文描述了新技术的原理、实验结果和实施问题。
