Development of the ultrasonic flowmeter.

The ultrasonic flow-velocity meter for blood flow measurement has developed in two directions. The first type is the transit-time velocity meter, and the second, the Doppler-shift type. For clinical measurement the transcutaneous Doppler instrument is now in routine use and has largely superseded the transit-time type. Doppler-shift velocity meters are now available which measure blood velocity, volume flow, flow direction, flow profile and visualize the internal lumen of a blood vessel.