AbstractThe incidence of disease of the cardiovascular system is very high and increasing worldwide, especially in the developing world. The radial and ulnar arteries are implicated in some important ailments where blood flow related parameters such as flow rate (FR), wall shear rate (WSR), arterial wall motion (AWM) and pressure, all of which can be measured using ultrasound techniques, are useful in diagnosis and patient management. However these measurements are prone to error due to the manner of image formation and the complex flow conditions within the vessels. In this thesis, the errors in ultrasound-measured parameters in the radial and ulnar arteries are investigated using experimental phantoms, computer simulation and on volunteers.
Using the Womersley theory, FR and WSR were estimated using a clinical ultrasound scanner with the pulsed wave (PW) mode and B mode. Experimental flow phantoms were designed to evaluate those measurements under different circumstances. A simulation technique which combined image-based computational fluid dynamics and ultrasound simulation was also used to evaluate ultrasound estimation of these parameters. A case study was then conducted on healthy volunteers to evaluate the method of measuring FR and WSR in-vivo. For the AWM in the radial artery, an auto-correlation method was used based on the radio-frequency (RF) data and validations were done by a flow phantom, simulation, and in-vivo trial. The blood pressure waveform in a volunteer’s radial artery was derived from the ultrasound measured AWM and compared with the waveform from a tonometry.
FR and WSR were both found to be overestimated by up to 50%, mainly due to the beam-vessel angle in the PW Doppler ultrasound. Measurement of the vessel diameter and assumption of the blood flow direction can also influence the estimations. Other factors, such as flow amplitude, vessel size, imaging depth and flow waveforms, do not seem to affect the estimation of these two parameters. Results taken from the flow phantoms agree with those from simulation and the estimations from the in-vivo case study also agree with the published data. The auto-correlation method for the AWM was validated from the phantom and simulation. It is able to detect motion amplitude of about tens of micrometres. The trial on volunteers proved the feasibility of this motion detection method. Blood pressure waveforms at the radial artery of a volunteer, derived from this ultrasound-measured wall motion and from the tonometry, were very similar.
The Womersley-based method is able to estimate the FR and WSR in the radial and ulnar arteries with high accuracy. Sources of the error and their magnitudes in estimation of the two parameters by ultrasound pointed out in this thesis are beam-vessel angle, vessel diameter measurement and flow direction assumption. Researchers and clinicians using these measurements in practice and research should be aware. The capability of ultrasound imaging to measure arterial AWM in the radial artery is demonstrated and it is found that the blood pressure waveform can also be derived from the arterial AWM.
|Date of Award
|China Scholarship Council
|Zhihong Huang (Supervisor), Peter R. Hoskins (Supervisor), George Corner (Supervisor) & Faisel Khan (Supervisor)
- Doppler ultrasound
- Flow phantom
- Arterial wall motion
- Radial and ulnar arteries