Multifrequency Doppler flowmeter: a way to rapid CW Doppler imaging

A single CW velocimeter for two-dimensional Doppler imaging yields a low frame rate because the single transducer pair must be moved in the x, y plane. The authors propose to increase the frame rate by measuring simultaneously the flow in several directions using several transmitter/receiver pairs, each with a unique emission frequency and having a separate CW velocimeter. The results obtained with a prototype composed of eight channels show that (1) the lateral resolution and the sensitivity of each channel are not affected by interference from the adjacent channels; and (2) it is possible to measure the flow simultaneously in multiple cross sections because the ultrasonic beams are independent.