Development of an ultrasound doppler flowmeter for measuring low blood flow velocities

Abstract

Ultrasound Doppler systems are widely used for flow measurement in both medicineand industry, having the advantages of being non-invasive and comparatively simpleand therefore inexpensive. However, these systems have not been applied to capillaryblood flow measurement because the velocities encountered are much smaller thanthose for which Doppler systems have so far been used, and also because ofdifficulties in separating the echoes from moving blood cells from the much strongerechoes derived from the stationary tissues which surround the capillaries.In this thesis, a system has been described to overcome some of the difficultiesencountered during small flow velocity measurements. A 2.25 MHz continuous-wave,non-directional Doppler flowmeter has been developed which is capable of measuringflow velocities below 2 cm/s. Ultrasonic transducers utilized in the system, and a flowphantom used to calibrate the flowmeter have also been produced.