[Laboratory experiment studies on quantitative blood flow measurement with the continuous-wave ultrasound Doppler procedure: I. Transducer evaluation].

Cw-Doppler transducers designed for volume blood flow measurement were evaluated experimentally. Both sensitivity plotting using a ball point reflector and comparative volume flow measurement on a flow-rig using EMF as reference method evidenced unequal sensitivity along the transducer. With increasing distance to the transducer the longer axis of the oval sound field assumed an orientation perpendicular to the longer axis of the active transducer surface. Sensitivity decreased from the centre of the sound field to its periphery. Differences of more than 2 mm between the length of the transducer and the diameter of the latex tube resulted in over- or underestimations of volume flow. Underestimations found with transducers longer than the tube diameter were interpreted as resulting from the increased contribution of stable echoes to the signal.