Some aspects of the relationship between instantaneous volumetric blood flow and continuous wave doppler ultrasound recordings—I. The effect of ultrasonic beam width on the output of maximum, mean and rms frequency processors

A theoretical model has been developed to predict the effect of ultrasonic beam width on the output of maximum frequency, mean frequency and rms frequency processors when interrogating blood vessels containing either parabolic or plug flow. It is shown that the only way to measure blood flow velocities, and obtain waveforms that are proportional to instantaneous volumetric flow (irrespective of changes in velocity profile) is to use an ultrasonic beam which is uniform over the whole area of the vessel, and to process the Doppler shift signal with a mean frequency detector.