Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 48-51). Also available in electronic version.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Proefschrift Universiteit Maastricht. / Auteursnaam op omslag: Koo de Priester. Met lit. opg. - Met samenvatting in het Nederlands.

Proefschrift Maastricht. / Lit. opg. - Met een samenvatting in het Nederlands.

This thesis presents three original contributions to the field of Nuclear Magnetic Resonance (NMR): The experimental framework and analysis for the measurement of a new imaging parameter to describe perfusion; The measurement and analysis of magnetic field inhomogeneity and a practical correction system for their reduction; A novel system for the synchronous control of NMR experiments based on the microprogrammed concept. The thesis begins with an introduction to the theory of NMR. The application of NMR to imaging is also introduced with emphasis on the techniques which developed into those in common use today. Inaccurate determination of the traditional NMR parameters (T1 and T2 and the molecular diffusion coefficient) can be caused by non-diffusive fluid movement within the sample. The experimental basis for determining a new imaging parameter - the Perfusion coefficient - is presented. This provides a measure of forced isotropic fluid motion through an organ or tissue. The instrumentation required for conducting NMR experiments is described in order to introduce the contribution made in this area during this research: A sequence controller. The controller is based on the concept of microprogramming and enables completely synchronous output of 128 bits of data. The software for the generation and storage of control data and the regulation of the data to provide experimental control is microcomputer based. It affords precise and accurate regulation of the magnetic field gradients, the rf synthesizer and the spectrometer for spectroscopic and imaging applications. Fundamental to the science of NMR is the presence of a magnetic field. A detailed study of the analysis of magnetic field inhomogeneity in terms of spherical harmonics is presented. The field of a whole body imaging system with poor inhomogeneity was measured and analyzed to determine and describe the components of the inhomogeneity. Finally a description is given of the design and application of practical methods for reducing the dominant inhomogeneities.

The design, construction and calibration of an intermediate scale NMR imaging system is described. The system is based on a 7" diameter, room temperature bore superconducting magnet at a field of 0.4T. Using selective excitation and projection reconstruction techniques, the production of density, spin-lattice and spin-spin relaxation weighted images has been achieved. An investigation of the feasibility of in-vivo tissue characterisation using NMR parameters has been carried out. Tissue characterisation using healthy animals of different ages, sex and species has shown that characterisation with the NMR parameters of T1** and T2** is feasible on a given system, where 1/T1** and 1/T2** are the spin-lattice and spin-spin relaxation rates calculated from the images assuming these rates to be mono-exponential. It is shown that the scatter in results which previously was believed by other authors to be due to biological variation is in fact due to experimentation and instrumentation, and that the biological limit has yet to be reached. The successful employment of quantitative characterisation in the observation and monitoring of diseased states is illustrated by two examples. The first shows the growth of a tumour and the second uses T1* to observe the effect of toxic drugs on the kidney. In the latter case, little evidence of damage was visible on the image. Following characterisation, it is demonstrated that it is possible to optimise an imaging sequence by careful selection of the timing parameters. Optimisation of the sequences used in this work gave an increase of upto a factor of two in the signal-to-noise ratio and increased the accuracy of the relaxation rate evaluation. Finally, a technique for obtaining a map of the spatial distribution of the molecular translational diffusion coefficient together with perfusion and flow information has been developed. These parameters may well enhance the contrast as well as providing new information on the biological system.

At the start of this work in 1988, apart from bulk relaxation experiments four authors had reported discrimination of oil from water in core samples under static conditions by MRI, and only one, Baldwin (1986) had reported visualisation of flowing oil and water using doping agents Mn++. The aim of this research was to develop the application of MRI to petroleum engineering and in particular to develop Enhanced Oil Recovery (EOR) techniques. A synergistic approach was adopted involving collaboration with AGIP Oil, Italy and the Petroleum Engineering Department of Imperial College. A systematic study of properties of the fluids and their interaction with rock types was mounted, to investigate suitable contrast mechanisms. This was followed by static and dynamic imaging experiments. The chemical shift imaging technique has been used to measure oil and water saturations during flooding experiments with Portland Limestone. For the first time MRI has been used to generate relative permeability, and fractional flow curves for a core plug. The capillary pressure gradient was also determined from the data. The new method was compared to the results of traditional core analysis. Miscible displacements in Lochaline Sandstone were then studied using D2O, glycerol and polymer solutions. The spin echo imaging technique was used to determine the angle of the interface between the fluids. This angle is determined by the ratio of viscous to capillary forces. From this information the core permeability (liquid) and polymer viscosity were measured. These measurements compared well with conventional methods and the results break new ground for MRI. The polymer viscosity measurements are of particular interest since the fluid is non-Newtonian. In separate experiments tertiary chemicals were identified directly during displacement experiments by MRI for the first time. Finally a new model system was developed for image calibration.

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