基于幅度加权的预失真线性调频超声编码激励

Predistorted Linear Frequency Modulation Ultrasound Coded Excitation Based on Amplitude Weighting

为了提高医学超声成像的轴向分辨力和确保对比度,该文提出一种基于幅度加权的预失真线性调频编码新方法。该方法将线性调频发射信号幅度加权技术和回波信号旁瓣抑制技术相结合,一方面补偿超声探头对发射信号的影响,使得回波信号的带宽不局限于探头,提高轴向分辨力;另一方面消除发射信号幅频特性的菲涅耳波纹,提高发射信号的带宽并采用失配滤波器进行脉冲压缩,实现旁瓣抑制,确保成像对比度。仿真结果表明:相对恒包络线性调频编码,预失真线性调频编码方法不仅提高了轴向分辨力,而且最大旁瓣幅度减小至-48 dB以下,满足医学成像对比度要求。FieldII仿真B超图像结果表明:恒包络线性调频和预失真线性调频编码方法的轴向分辨力分别是0.35 mm和0.25 mm。

In order to improve the axial resolution and satisfy the contrast resolution of medical ultrasound imaging, a predistorted Linear Frequency Modulation （LFM） coded excitation new method based on amplitude weighting is proposed. Combining the amplitude weighting technology of LFM transmitted signal with the sidelobe reduction technology of echo signal, the method on the one hand can compensate the influence of transducer impulse response on transmission signal, so bandwidth of the echo signal is not limited by the transducer and axial resolution is improved. On the other hand, the method can remove the Fresnel ripples of transmitted signal＇s frequency response increase its bandwidth and use mismatched filter for pulse compression, so range sidelobe is suppressed to ensure contrast resolution. The results of simulation reveal that in contrast with constant envelope LFM coded excitation, the predistorted one can improve axial resolution and reduce maximum sidelobe at -48 dB to satisfy contrast resolution of medical imaging. FieldII Simulation results of B-mode image show that the axial resolution of constant envelope LFM coded excitation and the predistorted one is 0.35 mm and 0.25 ram, respectively.