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Title: Advanced design and experimental validation of MRI contrast agents for fluid pressure mapping using microbubbles
Author: Morris, Robert H.
ISNI:       0000 0004 2678 2768
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2009
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This work is related to monitoring fluid pressure using Magnetic Resonance Imaging or MRI and includes numerical simulations and experimental MRI. The nature of this study is such that techniques other than MRI have been extensively used to assess the contrast agent for its physical behaviour. These techniques include rheometry, light scattering, optical and scanning electron microscopy. Six MRI experiments in total were performed: The first two experiments use standard spin echo imaging techniques to test various lipid preparations which are then used as a contrast agent to pressure in a porous medium. The remaining experiments are performed using a fast imaging technique and investigate various improvements to the contrast agent which resulted in the development of an agent exhibiting an unprecedented level of sensitivity. A variety of lipid preparations are utilised throughout the experiments. Initial testing reveals that the DSPC lipid offers the greatest stability, although a fluorinated lipid is used in a later study for an improved synergy between the shell and gas microbubble components. Having assessed the microbubble stability, preparations are prepared as in the work previously published in the area. This preparation is tested in two porous media to investigate the sensitivity of the contrast agent to changes in pressure. A sensitivity of 20% signal change per bar is found in porous media although a drift of 11%h-1 is also observed. An improved preparation was then developed by using an alternative polysaccharide gel, gellan gum. This medium allows a large increase in viscosity without compromising the diffusion coeffcient of water throughout the gel network which is of key importance to the sensitivity of the technique. The suitability of the new preparation is assessed using viscosity, turbidity, diffusion and MRI measurements. The results show that a very stable contrast agent, demonstrating a sensitivity of 38% signal change per bar and negligible drift has been produced. The contrast agent is then developed further to produce a soft solid for potential applications in granular dynamics. By cross linking another polysaccharide gel, carageenan gum, into which the microbubbles have been mixed, a contrast agent has been successfully tested. This agent is again assessed using diffusion and elastic stress measurements which demonstrate its suitability to monitor pressure. Abstract 12 Using a wide range of techniques including time lapse photography, rheology, diffusion NMR and MR imaging, contrast agents have been produced which meet specific applications. Contrast agents in both solid and liquid phases have been produced to allow measurements in porous media and in granular dynamic systems. These contrast agents have been optimised in terms of the lipids used for the microbubbles, the chemistry used for production of the suspending media, the protocols for production, assessment and application of each agent and MRI sequences used to collect images. In doing so a reliable method for tailoring contrast agents to pressure has been developed leading to novel experimental measurements which may be applicable to oil recovery and medicine alike.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available