An experimental and theoretical investigation of the wall-effect in doppler ultrasound flow phantoms 

Abstract

The wall of blood-vessel-mimicking plastic tubes used in medical ultrasound Doppler flow phantoms causes the acoustic pressure within the phantom tube to be distorted from that which would occur within a healthy blood vessel were both subject to the same incident acoustic field. This distortion causes the Doppler spectrum from the phantom to differ from that found in vivo. The aim of this thesis is to quantify the effect of different phantom tubes on this distortion so that a recommendation can be made for a least-distorting tube. The factors considered include reflection, refraction and absorption with inclusion of all mode conversions between shear and longitudinal modes. Most tube materials previously used in flow phantoms, from Cflex to quartz glass, were considered. The pressure is found both by use of the infinite absorbent plate theory and also by the theory of infinite, absorbent cylindrical shells with a finite ultrasound beam. This pressure is then used to predict the Doppler signal level from a thread moving within the phantom tube in a direction parallel to the tube axis. This prediction at 4Mhz was then compared with experimental measurements. Doppler spectra from steady flow within the tubes were also computed. The study confirmed that harder tubes, such as PMMA and LDPE, cause severe distortion within the tubes. The effect of the reflection back into the lumen off the inside back-wall of the tube was a major cause of the distortion in these tubes. PTFE and Cflex tubes caused the least distortion of those studied and thick-wall (1.6mm) Cflex was thus recommended as the least-distorting tube. The temperature coefficient of Cflex acoustic absorption at room temperature was measured as - 5.5%/º C. A novel explanation for the 'beamstring angle effect' for monofilament strings was also suggested.

Date of Award	1998
Original language	English
Awarding Institution	University of Wales, Bangor
Supervisor	Peter Fish (Supervisor), Steve Bone (Supervisor) & John Cope (Supervisor)