A new pulsed wave Doppler ultrasound system to measure bloodvelocities beyond the Nyquist limit

Conventional pulsed wave (PW) Doppler ultrasound systems measure blood velocities unambiguously as long as the velocities are less than the Nyquist velocity. Here, a new PW Doppler ultrasound system is described, which can measure velocities up to 4.5 times higher than the Nyquist velocity. The new PW system presented here utilizes two ultrasound carrier frequencies, such that an appropriate processing of the Doppler frequencies results in an extended mean-velocity range. With this extended mean-velocity information, the complex Doppler signal is interpolated to reconstruct aliased Doppler spectra. The interpolation algorithm has been tested by computer simulations demonstrating the capabilities and limits. The integration into a commercial Doppler scanner allowed the evaluation of the new PW system in real time. In vitro and in vivo tests demonstrate the effective reconstruction of highly aliased Doppler spectra