DETECTION OF LOW-GRADE ARTERIAL-STENOSIS USING AN AUTOMATIC MINIMUM-FLOW-VELOCITY TRACKING SYSTEM (MVTS) AS AN ADJUNCT TO PULSED ULTRASONIC DOPPLER VESSEL IMAGING

A microprocessor-controlled system for detecting minor flow disturbances in blood vessels is described. The system is composed of a multigated pulsed Doppler ultrasonic velocimeter (MAVIS) and an 8085 microprocessor acting as an interface for a signal processing system and/or a storage system. A minimum-particle-velocity method is used to extract Doppler signals from selected sites as near as possible to the vessel wall. These Doppler signals can be monitored constantly during any vessel scanning procedure revealing flow abnormalities caused by stenoses of as little as 15% area reduction. The performance of the microprocessor-controlled system was assessed using signals generated electronically. For the in vitro assessment of the system as a whole a test rig which generates pulsatile flow through nonsymmetric stenoses varying from 15-30% area reduction was used. The study shows the development of disturbed flow not only downstream, but also upstream of the stenosis. The results show the capability of this method in discriminating flow disturbances caused by minor stenoses. Preliminary in vivo assessment was carried out in patients with suspected carotid artery disease and the results have indicated how this method can be used to localize the exact position where flow disturbance is occurring.