Spectral Doppler technique with extended unambiguous velocity range

A hybrid pulsed wave Doppler technique is proposed which combines high pulse repetition frequency (HPRF) operation with inter-pulse encoding and 2D-FFT processing. A windowed, linear FM-chirp of ascending pitch, and its time-reversed copy, are used to encode alternate transmit firings at doubled the maximum PRF based on the round-trip distance between the Doppler sample gate and the transducer. Three key properties of the chirp pair are described which enable 1) HPRF operation with significant suppression of the ghost sample gate sensitivity profile; and 2) 2D-FFT spectral analysis which strongly reduces speckle variance. Selected simulation results are presented based on synthesized RF signals for 3 MHz Doppler, 20-cycle chirps and typical pulsatile flow parameters.