The application of cross-correlation method in blood flow sonography

The conventional Pulsed Wave (PW) Doppler blood flow analyzers with the sonogram display are widely used in clinical diagnosis. However, the system suffers from spectrum aliasing problems when the velocities exceed the Nyquist limit. Time domain Cross-Correlation (CC) method is superior to PW in the high velocity measurements. But, instead of the sonogram, the CC method can only provide the average velocity in the sample volume. Combining the PW with the CC method, the authors propose a joint CC-PW method which takes advantage of the sonogram output, but overcomes the aliasing problems. With this new method, the delay times of the received RF echoes from pulse-to-pulse are estimated by the CC method. The series of delay time with the related maximum value in cross-correlation function are then used to form a time sequence, which is finally sent to a spectrum analyzer to produce the sonogram. The principle of the method is described in detail and experimental results are given in the paper