P1A-1 Phase Domain Velocity Estimation in Medical Ultrasound with Linear Frequency Modulated Chirps: A Simulation Study

A simulation study is presented which investigates the possibility of obtaining better spatial resolution and similar or improved statistical performance from a coded waveform compared to a continuous frequency (CF) narrowband pulse for colour flow imaging (CFI) applications. Our attention is focused on linear frequency modulated (LFM) chirps. We show that it is possible to improve the spatial resolution and the signal to noise ratio (SNR) conditions with moderately long LFM chirps (10 mus), but an increase in spatial resolution strongly limits the SNR gain provided by the coded excitation signal over conventional long CF pulses. We then study through simulations the possible impact of using LFM chirps for velocity estimation with two standard phase domain algorithms, the Kasai algorithm and the modified autocorrelation. The use of coded excitation is beneficial in terms of statistical performance for a rather low range of SNR (5-10 dB). For a medium range of SNR (20-30 dB) the performance of phase domain estimators appears to be essentially driven by the bandwidth of the transmitted waveform, which suggests a trade-off between resolution and performance in the use of coded waveforms with this type of estimator.