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Investigation of ultrasound-measured blood flow related parameters in radial and ulnar arteriesZhou, Xiaowei January 2017 (has links)
The 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.
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Validation of a 1D Algorithm That Measures Pulse Wave Velocity to Estimate Compliance in Blood VesselsLeung, James 01 June 2018 (has links) (PDF)
The purpose of this research is to determine if it is possible to validate the new 1D method for measuring pulse wave velocity in the aorta in vivo and estimate compliance. Arterial pressure and blood flow characterize the traveling of blood from the heart to the arterial system and have played a significant role in the evaluation of cardiovascular diseases. Blood vessel distensibility can give some information on the evolution of cardiovascular disease. A patient’s aorta cannot be explanted to measure compliance; therefore we are using a flow phantom model to validate the 1D pulse wave velocity technique to estimate compliance.
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Particle image velocimetry measurements of blood flow in aneurysms using 3D printed flow phantomsTshimanga, Ilunga Jeanmark 11 1900 (has links)
Cardiovascular diseases (CVD) remain one of the leading causes of deaths worldwide. The formation and
presence of aneurysm is a very important question in the study of this CVDs. An aneurysm is a balloon-like
bulge on a blood vessel which forms over time. An aneurysm is usually considered to be a result of weakening
of the blood vessel walls, this definition has stood over many years without being conclusively proven.
Eventually, the aneurysm could clot or burst due to degradation of the aneurysm wall and accumulation of
blood. The latter would lead to internal bleeding and result in a stroke. Local hemodynamics have been found
to be very important in the study of the evolution of an aneurysm. In this study, a steady flow experimental
investigation was conducted using planar Particle Image Velocimetery (PIV) on a rigid flow phantom of an
idealised geometry consisting of a curve parent artery and a spherical aneurysm located on the outer convex
side of the curvature. The flow phantom was fabricated directly using a commercially available desktop
Stereolithography (STL) 3D printer instead of the more conventional investment casting method using a core.
Although 3D printing technologies have been around for many years, the fabrication of flow phantoms by
direct printing is still largely under-explored. This thesis details the results of investigation into the optimal
printing and post-printing procedures required to produce a flow phantom of suitable clarity and transparency.
Other important areas of concern such as the geometric accuracy, surface topography and refractive index of
the final model are also investigated. A planar PIV is conducted to study the impact of flow rates on the local
flow field in and around the aneurysm and their impact on the wall shear stress. It was found that direct 3D
printing is appropriate for the fabrication of flow phantoms suitable for PIV or other flow visualisation
techniques. It reduces the complexities and time needed compared to the conventional investment casting
methods. It was observed that the optical properties of the printed material such as the high refractive index
(RI) and the transmittivity of light could cause a problem in large models. From the PIV measurements it was
found that flow rates affect the flow field in both the parent artery and the aneurysm. First, high velocities
were observed on the outer curvature of the parent artery. Secondly the centre of rotation in the aneurysm is
not at the geometric centre but is displaced slightly in the direction of the flow. Finally, the flow rate affects
the angle in which flow enters the aneurysm from the parent vessel. This change in the flow angle affects the
flow within the aneurysm. A higher flow rate in the parent artery increases the incident angle which brings the
centre of rotation closer to the geometric centre of the aneurysm, this changes the location and magnitude of
high velocities and hence the local wall shear stress (WSS) on the wall of the aneurysm. This may have
implications in the evolution of aneurysms. / Mechanical and Industrial Engineering
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Investigation of Laser Speckle Contrast Imaging's Sensitivity to FlowYoung, Anthony M. 30 July 2018 (has links)
No description available.
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Monitoring Cerebral Functional Response using sCMOS-based High Density Near Infrared Spectroscopic ImagingLangri, Dharminder Singh 02 August 2019 (has links)
No description available.
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Fluid dynamic assessments of spiral flow induced by vascular graftsKokkalis, Efstratios January 2014 (has links)
Peripheral vascular grafts are used for the treatment of peripheral arterial disease and arteriovenous grafts for vascular access in end stage renal disease. The development of neo-intimal hyperplasia and thrombosis in the distal anastomosis remains the main reason for occlusion in that region. The local haemodynamics produced by a graft in the host vessel is believed to significantly affect endothelial function. Single spiral flow is a normal feature in medium and large sized vessels and it is induced by the anatomical structure and physiological function of the cardiovascular system. Grafts designed to generate a single spiral flow in the distal anastomosis have been introduced in clinical practice and are known as spiral grafts. In this work, spiral peripheral vascular and arteriovenous grafts were compared with conventional grafts using ultrasound and computational methods to identify their haemodynamic differences. Vascular-graft flow phantoms were developed to house the grafts in different surgical configurations. Mimicking components, with appropriate acoustic properties, were chosen to minimise ultrasound beam refraction and distortion. A dual-beam two-dimensional vector Doppler technique was developed to visualise and quantify vortical structures downstream of each graft outflow in the cross-flow direction. Vorticity mapping and measurements of circulation were acquired based on the vector Doppler data. The flow within the vascular-graft models was simulated with computed tomography based image-guided modelling for further understanding of secondary flow motions and comparison with the experimental results. The computational assessments provided a three-dimensional velocity field in the lumen of the models allowing a range of fluid dynamic parameters to be predicted. Single- or double-spiral flow patterns consisting of a dominant and a smaller vortex were detected in the outflow of the spiral grafts. A double- triple- or tetra-spiral flow pattern was found in the outflow of the conventional graft, depending on model configuration and Reynolds number. These multiple-spiral patterns were associated with increased flow stagnation, separation and instability, which are known to be detrimental for endothelial behaviour. Increased in-plane mixing and wall shear stress, which are considered atheroprotective in normal vessels, were found in the outflow of the spiral devices. The results from the experimental approach were in agreement with those from the computational approach. This study applied ultrasound and computational methods to vascular-graft phantoms in order to characterise the flow field induced by spiral and conventional peripheral vascular and arteriovenous grafts. The results suggest that spiral grafts are associated with advanced local haemodynamics that may protect endothelial function and thereby may prevent their outflow anastomosis from neo-intimal hyperplasia and thrombosis. Consequently this work supports the hypothesis that spiral grafts may decrease outflow stenosis and hence improve patency rates in patients.
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