A method is provided for employing a transit time ultrasound sensor, wherein the sensor can be used for the measurement of liquid flow in a conduit, the sensor having an acoustic path formed of materials matched in ultrasound properties to a flow under test, and designed to conform to the shape of the conduit. The transit time ultrasound sensor can be configured as a clamp on device, wherein the conduit walls are constructed from such an ultrasonically-matched material. Alternately, the transit time ultrasound sensor can be employed in a perivascular configuration, wherein the ultrasonically-matched material is operably intermediate the blood vessel and the sensor.