彩色超声血流成像中基于回波频率跟踪的正交解调方法

为了消除由超声频率下移所引起的血流速度估计精度的下降,提出了一种基于回波频率跟踪的正交解调方法。首先建立了回波中心频率随深度下移的线性模型;然后使用传统I/Q(Inphase/Quadrature)解调方法得到有偏的基带信号,采用自相关方法沿深度方向分段估计中心频率的下移量,并利用估计出的这些值对所建立的线性模型进行拟合;最后利用拟合后的模型来实时跟踪回波的中心频率,并将其作为参考频率再进行I/Q解调。仿真和试验结果表明,基于回波频率跟踪的正交解调方法能够得到近似无偏的基带信号,提高血流速度估计的准确度和精度,改善彩色超声血流成像的质量。

A quadrature demodulation technique based on echo-frequency tracking in ultrasound color flow imaging

A quadrature demodulation method based on echo-frequency tracking is proposed to eliminate the flow velocity estimation error caused by ultrasound frequency downshift.First a linear model is established for the central frequency downshift along depth direction.Then the frequency downshifts along depth are estimated through autocorrelation technique based on the biased base-band signal obtained by conventional I/Q (Inphase/Quadrature) demodulation, and the estimated values are used for fitting the linear model.Finally the central frequencies are tracked by the fitted model,and used as the reference frequencies for I/Q demodulation.Simulation and experimental results show that nearly unbiased base-band signal can be obtained by the proposed demodulation method,so that the flow velocity estimation can be more accurate and the quality of ultrasound color flow imaging can be improved.