A tracking FFT processor for pulsed Doppler analysis beyond the Nyquist limit (medical ultrasound)

The processor is based on the observation that the frequency translation required to reconstruct properly an aliased spectrum can be achieved by means of a simple reordering of data provided by a digital fast Fourier transform (FFT) unit. The amount of reordering is automatically derived by the computed value of a spectral parameter, e.g. the mean frequency. The procedure has been tested by introducing some modifications at the output of an FFT unit included in a conventional pulsed Doppler system. The dynamic evolution of the full Doppler spectrum and related mean frequency can be followed in real time over an extended range. Results of in vitro and in vivo experiments, as well as quantitative measurements performed with test signals, are presented.