Color coded ultrasonic differential velocity arterial scanner (Echoflow).

Abstract A scanning system is described which is capable of making a two dimensional display of the blood flowing in arteries. It has been especially designed for display of the carotid bifurcation but can be adapted for other blood vessels. Normally it uses continuously generated energy and detects the Doppler shifted signals from the blood flowing in the arteries at peak velocity as the arterial pulse propagates through the segment of vessel being scanned. The system is directional so that flow in only a single direction with reference to the beam is displayed at any one time. The Doppler shifted signals reflected by the blood flowing at peak velocity are detected by filters with varying frequency ranges. Signals from each filter activated are color-coded. The color display is made from the filter activated by the highest Doppler frequency shifted signals. Thus the arteries are displayed by colors corresponding to the highest peak velocities in their segments. Stenotic areas where peak velocities will be greater than in non-stenosed regions will thus be displayed by colors differing from that used to represent normal peak velocities. These regions of increased peak velocities correlate reliably in 95% of cases with arterial stenoses occluding more than 74% of the arterial diameter. Occluded vessels which do not appear at their appropriate position on the image are also reliably displayed in 95% of cases. The display of normal carotid bifurcations by normal colors in the Doppler scan is also reliable in 93% of cases but the display of slightly increased velocities may result from haemodynamic causes as often as from localized small stenoses.