Mean blood velocity measurement with a narrow ultrasound beam and an asymmetric velocity profile

Previous discussions of the measurement of spatial mean blood velocity using Doppler ultrasound with a narrow beam have required the velocity profile in the cross section to be symmetric about the vessel axis. A type of asymmetry is put forward which incurs no error in mean velocity measurement when the beam is directed through the paint of maximum velocity. Assuming correct alignment of the beam, errors due to profile asymmetry are, therefore, related to the degree of departure of the asymmetry from this acceptable form.