Blood flow detection by an intersecting zone ultrasonic Doppler unit

A continuous wave Doppler system has been constructed with which a localised region may be studied by arranging for the transmission zone and the reception zone of the beam to intersect at the selected region. This intersecting zone technique overcomes the problem of lack of localisation normally associated with continuous wave Doppler devices while retaining the low noise and high velocity measurement features of these instruments. The variable intersecting zone Doppler unit has been linked with a real-time ultrasonic scanner to study blood flow in the pregnant uterus. Sites studied include the placenta, the cord, the foetal aorta and umbilical vein.