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Comparison of time and frequency domain approaches for blood velocity estimation in small vessels using high frequency ultrasound

Approaches for axial blood velocity estimation with pulsed wave Doppler (PWD) systems can be separated into time domain, frequency domain and combined time and frequency domain techniques. The imaging properties (spatial and velocity resolution) with these approaches are different and depend on the resolution cell size (determined by bandwidth and lateral resolution), measurement time (number of A-lines included into velocity estimation) and flow geometry (insonification angle, vessel diameter relative to resolution cell size, flow velocity profile). Simulations have been performed to analyze the imaging properties under different parameter settings and to find optimal settings for blood flow imaging in small vessels, where the flow velocity profile changes significantly over the resolution cell. The findings were validated with flow phantom measurements and in vivo measurements on small blood vessels at the back of a human hand using a high frequency (30-70 MHz) PWD-system.