Zhao Heng, Mo Larry Y L, Gao Shangkai
Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China.
IEEE Trans Ultrason Ferroelectr Freq Control. 2007 Feb;54(2):319-31. doi: 10.1109/tuffc.2007.246.
Barker-coded excitation is applied to improve the sensitivity versus resolution tradeoff for ultrasound color flow imaging (CFI). Direct sequence encoding and complex baseband decoding methods that enable flexible combination of demodulation frequency and Barker-chip duration are proposed. Based on a general Wiener decoding filter formulation, three different conditions that pertain to the relationship between the Barker-chip duration and demodulation frequency are found, such that they result in real, complex symmetric and complex asymmetric decoding filter sequences, respectively. It is also shown that the matched filter and the inverse filter represent two extreme cases of the Wiener filter, and the latter is proposed for decoding Barker-coded CFI signals with maximum range sidelobe suppression. Some practical considerations such as coding gain, integrated sidelobe level (ISL) and peak sidelobe level (PSL) for various decoding filter lengths, and the influence of flow rate also are analyzed. Linear array imaging of steady flow in straight tubes is simulated based on a 4-cycle base pulse at 6.25 MHz, a 5-chip Barker code, a 32-tap decoding filter, and standard color flow data processing. The resultant color flow images demonstrate the expected improvements in penetration and axial resolution.
应用巴克码编码激励来改善超声彩色血流成像（CFI）中灵敏度与分辨率之间的权衡。提出了直接序列编码和复基带解码方法，这些方法能够灵活组合解调频率和巴克码片持续时间。基于一般的维纳解码滤波器公式，发现了与巴克码片持续时间和解调频率之间关系相关的三种不同情况，它们分别导致实、复对称和复非对称解码滤波器序列。还表明匹配滤波器和逆滤波器代表了维纳滤波器的两种极端情况，并且提出使用后者来解码具有最大距离旁瓣抑制的巴克码编码CFI信号。还分析了一些实际考虑因素，例如各种解码滤波器长度的编码增益、积分旁瓣电平（ISL）和峰值旁瓣电平（PSL）以及流速的影响。基于6.25MHz的4周期基脉冲、5码片巴克码、32抽头解码滤波器和标准彩色血流数据处理，模拟了直管中稳定血流的线性阵列成像。所得的彩色血流图像显示出在穿透性和轴向分辨率方面的预期改善。
