Study of the AQD spectral estimator on simulated and in vivo Doppler data

This paper studies a novel spectral estimator the adaptive-Q distribution (AQD), and its applicability to simulated and in vivo Doppler data. The AQD uses a priori knowledge about the signal's instantaneous frequency, and bandwidth. Simulated Doppler data were generated using a comprehensive model that accounts for both hemodynamic and acoustic factors. In vivo data were acquired with a 10 MHz ultrasound cuff transducer positioned around the distal aorta of a rabbit. First, the model was validated by comparison with the Womersley equation. The small median error found (3.5%) is important, because pulsatile flow is not always parabolic and requires attention different from that in steady flow. Next, the Womersley parameters were obtained for the in vivo data, based on vessel geometry and pressure waveform. Finally, these parameters were used in the simulation to compute a "theoretical spectrum". The AQD achieved a better tradeoff (109% root mean square error versus 151%) between reducing variance and preserving resolution than the short-time Fourier transform (STFT) for in vivo data.