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

Abstract

A tracking procedure for processing ultrasound pulsed Doppler signals with instantaneous frequencies beyond the Nyquist limit is discussed. It is based on the observation that the frequency translation required to properly reconstruct 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. As a result, the dynamic evolution of the full Doppler spectrum and related mean frequency can be followed in real time over an extended range. In vitro and in vivo experiments, as well as quantitative measurements carried on with test signals are presented.