It is shown that time domain correlation can be used to estimate the volumetric flow in a vessel accurately without deteriorating effects due to the frequency-dependent attenuation of ultrasound. When the transmitted pulses are separated by a certain time and are reflected by the moving scatterers within the ultrasound beam, the time difference between the pulses changes. The observed time shift is directly related to the radial speed (relative to the beam axis) of the scatterers. If the flow velocity is sampled at different positions across the vessel, then the volume flow rate can be calculated. The time domain technique has been verified in a blood flow phantom using a blood mimicking substance and natural sponge as the attenuating medium beween the transducer and the vessel. For hydrodynamically determined flow rates from 50 to 560 ml/min, the continuous volumetric flow has been ultrasonically assessed with an accuracy better than 21%.
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