Sogang Institute of Advanced Technology, Sogang University, Seoul, Korea.
IEEE Trans Ultrason Ferroelectr Freq Control. 2011 Feb;58(2):327-37. doi: 10.1109/TUFFC.2011.1810.
Spatial resolution of an ultrasound image is limited by diffraction of ultrasound as it propagates along the axial direction. This paper proposes a method for reducing the diffraction spreading effect of ultrasound by using a synthetic aperture focusing (SAF) method that uses plane waves instead of spherical waves. The new method performs data acquisition and beamforming in the same manner as conventional SAF methods. The main difference is that all array elements are used on each firing to generate a plane wave, the traveling angle of which varies with the position of a receive subaperture. On reception, each scan line is formed by synthesizing RF samples acquired by relevant receive subapertures with delays to force the plane waves to meet at each imaging point. Theoretical analysis and computer simulation with infinite transmit aperture show that the proposed method is capable of suppressing the diffraction of ultrasound and especially causing the lateral beam width to remain unchanged beyond a certain depth determined by the size of a receive subaperture and the maximum traveling angle of plane waves. It is demonstrated that the proposed method is realizable using a linear array transducer. It is also shown that the lateral radiation pattern produced by the proposed method has smaller beam width than that using conventional SAF methods in the region of interest because it suppresses the diffraction of ultrasound.
超声图像的空间分辨率受到超声在轴向传播时的衍射限制。本文提出了一种通过使用平面波而不是球面波的合成孔径聚焦（SAF）方法来减少超声衍射扩展效应的方法。该新方法以与传统 SAF 方法相同的方式进行数据采集和波束形成。主要区别在于，在每次发射时都使用所有的阵元来生成一个平面波，该平面波的传播角度随接收子孔径的位置而变化。在接收时，每条扫描线通过延迟合成相关接收子孔径中获取的 RF 样本来形成，以迫使平面波在每个成像点相遇。具有无限发射孔径的理论分析和计算机模拟表明，该方法能够抑制超声的衍射，特别是在由接收子孔径的尺寸和平面波的最大传播角度决定的一定深度之外，使横向波束宽度保持不变。证明了该方法可以使用线性阵列换能器实现。还表明，由于抑制了超声的衍射，该方法产生的横向辐射模式在感兴趣区域的波束宽度比使用传统 SAF 方法的波束宽度小。
