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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The keto-enol tautomeric systems of cyclic 1,3 diones have been studied by the proton magnetic resonance method. The presence of both keto and enol forms were confirmed in chloroform and acetonitrile solutions . From the concentration dependence of OH proton chemical shift, the equilibrium among the three forms has been suggested: (formula omitted). A linear relationship was found between the OH proton chemical shift and l/√c. The chemical shift of the hydrogen bonded OH proton was found to be -740 cps from T.M.S. at 60 M.c. by extrapolation to infinite concentration. That of the non-hydrogen bonded OH proton was found to be -440 cps, which gave the most reasonable equilibrium constant, K₁ , for all concentrations. The equilibrium constants were obtained from the observed OH chemical shift and from the ratio of the areas under the specific peaks for each species. Measurements were also made in the temperature range 302°K to 357°K for cyclohexane 1,3 dione in chloroform. The overall heat of conversion from the dimer enol form to the monomer keto form was found to be 2.05 Kcal/mole. The proton magnetic resonance spectra of methyl pyridines have been investigated both in carbontetrachloride and trifluoroacetic acid. The broad triplets which were observed at the pyridine concentration of 6~8 mole %, in trifluorocacetic acid confirmed the presence of the pyridine cations . Almost, all the signals, shifted to low field on protonation. The factors which affect the chemical shift were split into several terms on the basis of Pople's theory.¹²⁵ The chemical shifts of the pyridine and pyridinium systems were compared with the benzene system. Dominating factors were found to be; the inductive and anisotropic effects of the nitrogen atom or the protonated nitrogen atom, the mesomerlc effect of the above, and the inductive and anisotropic effects of the methyl groups. Using these values, which were obtained from the simple compounds, the chemical shifts were calculated and compared with the observed values. They agreed in most of the cases within ± 5 cps at 60 M.c. The ortho coupling constants between the 2 and 3 ring protons in the puridine system are much smaller than those in the benzene system. The slight increases in coupling constants on protonation were only understandable considering the pyridinium cations as odd sequences from the benzene and pyridine systems. It was observed that the C¹³-H¹ coupling constants increased on protonation as a result of the increase in the electronegativity of the nitrogen atom. That is the s character in the carbon atomic orbital increased on protonation. / Science, Faculty of / Chemistry, Department of / Graduate

The magnetic resonance signal of a spin system quantized in the rotating reference frame was observed. The experiment consisted of subjecting the electron spins in solid 2,2 Diphenyl-l-Picrylhydrazyl (DPPH) to a strong r.f. field in the 8 mm. microwave range and observing the Larmor frequency corresponding to the effective field of the rotating frame. Signals from 7 to 52 Mc/s were observed. The results are compared with the theory developed by Redfield for this case, utilizing the concept of a spin temperature. Also observed were the Overhauser and Solid effects, which are two possible ways in which a net polarization of one spin species (in this case the protons in DPPH) may be achieved from the spin-spin coupling to another spin species (the electrons in DPPH). The enhancements obtained (60 and 100 respectively) are higher than those so far reported, although experimental errors make detailed comparisons questionable. The Solid effect is compared with a simplified theory of enhancement utilizing the spin temperature concept, and put forward by I. Solomon. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

High resolution nuclear magnetic resonance is used to investigate proton exchange in two hydrogen bonded systems. The change of the chemical shift of the acid proton with concentration in mixtures of trifluoroacetic acid and quinoline have been used to indicate the formation of a strongly hydrogen bonded ion pair in the pure acid-base system and in acetonitrile as solvent. Spectra at -18°C show resolved peaks for the ≽NH⁺ and -COOH protons confirming the nature of the exchange process. The kinetic processes involved in the exchange are discussed but the experimental difficulty in carrying out a low temperature (0 to -60°C) study of an equimolar mixture of the two components prevents any detailed investigation of the rate processes. The chemical shifts measured for the acid and hetero-ring protons are averages for the various environments so that charge density changes on protonation of a basic species are not proportional to the observed chemical shift changes. Intermolecular hydrogen bonding and proton transfer rates between methanol and orthochlorophenol have been experimentally investigated in the slow exchange approximation for the modified Bloch Equations (0°C to -41.1°C). Interpolations of the results to the fast exchange limit are consistent with experimental line widths in this region. The activation energy obtained for the first order kinetics is 4.58 Kcal mole⁻¹. It is considered that the intramolecular hydrogen bond in orthochlorophenol does not impede the proton exchange process in the two component system. Variations in the line width of the exchange averaged -OH resonance signal are used to indicate the effect of small quantities of water added to the methanol-orthochlorophenol mixtures. / Science, Faculty of / Chemistry, Department of / Graduate

The chemical shift of protons in intramolecular hydrogen bonds has been measured in 41 ortho substituted phenol type compounds. The change in chemical shift " ΔσOH " on formation of these hydrogen bonds is taken as the difference between the infinite dilution chemical shift of the parent phenol compound in CCl₄ solution and the chemical shift measured for the proton in the intramolecular hydrogen bond. This change in chemical shift is correlated with the corresponding frequency shift " ΔνOH " in the -OH stretching region of the infra-red spectrum. The dilution chemical shift for the -OH proton in the o-halophenols has been investigated over a concentration range 1-5 mole % in CS₂ and a temperature region -53 to 107°C Using the infinite dilution shift values, the equilibrium constants of the cis-trans conversion were obtained. Values for δCIS, the chemical shift of the completely hydrogen bonded form; δ TRANS, the chemical shift of the unbonded form, and ΔH , the enthalpy of formation of the hydrogen bond, were also calculated. From these results a value for ΔH, the enthalpy of formation for the dimer was calculated, assuming that the major dimer species in solution was formed from the combination of a cis and trans bonded form. Temperature studies of the change in chemical shift of the -OH proton for 2,1,6-trihalosubstituted phenols is also reported. The temperature range in this case was 0°C to 111°0. / Science, Faculty of / Chemistry, Department of / Graduate

Proton magnetic resonance has been studied in methane and its deuterated modifications. Measurements of relaxation time were carried out at a frequency of 30 Mc/sec. using pulse techniques. The spin-lattice relaxation time has been measured in liquid and solid samples of CH₄, CH₃D, CH₂D₂ and CHD₃ between 110°K to 56°K. The simplest possible interpretation of our results in both the liquids and solids is that only one mechanism, that associated with the inter-molecular interactions, is probably predominant in causing relaxation. The spin-rotational and intra-molecular dipolar interactions do not seem to contribute appreciably to relaxation. The effect of dissolved paramagnetic ions has also been studied in samples of CH₄ between 110°K - 78°K and we have developed a very simple and reliable technique for obtaining oxygen-free samples in order to study T₁ in pure samples because T₁ has been found by us to be very sensitive to small, amounts of oxygen. The results verify the invers proportionality of T₁ to the oxygen concentration. The spin-spin relaxation time T₂ has been measured in liquid and solid samples between 110°K and 56°K. The results show that the line shape is predominantly due to inter-molecular interactions. Furthermore the resonance line has a gaussian shape at temperatures below 65°K and changes to a Lorentzlan shape at higher temperatures. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A field modulated super-regenerative spectrometer was constructed. The theory of its operation was developed and put to test by observing the pure quadrupole resonance of Chlorine 35 in Para - di-chlorobenzene powder at room temperature. The spectrometer's operation is closely related to the quadrupole transient effects. So another experiment was done to measure the amplitude and the decay time constant of Free Induction Signal in Para-di-chlorobenzene as a function of pulse width and magnetic field, using a pulsed r.f. transmitter, constructed for this purpose, The results of this experiment were then applied to the theory of the spectrometer to explain its behaviour. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Nuclear magnetic resonance and infra-red studies have been made of various clathrate compounds. The purpose of the investigations was to examine the extent of molecular motion which the enclathrated molecule^ may undergo. It has been shown that the benzene molecule in the clathrate with Nickel Ammonium Cyanide rotates about the six-fold axis at room temperature. The existence of shifts in the infra-red spectrum of the enclosed molecule has been confirmed but the assignment of the absorption bands at 1573 cm-¹ and 1165 cm-¹ as the Raman active E[subscript 2g] vibrations is incorrect. Studies on the quinol clathrates of methane, fluoroform, methyl alcohol and methyl cyanide and the clathrate of sulphur hexafluoride in Dianin's compound (4-p-hydroxyphenyl-2,2,4-trimethyl chroman) infer that isotropic motion of the enclathrated molecues occurs at 77°K. The infra-red spectra of these clathrates and of quinol 0-d₂ have been examined. Nuclear magnetic resonance investigations of molecular motion in weak charge transfer complexes are reported. In the dioxane complexes of bromine and mercuric chloride the structure is rigid at room temperature. In the complexes with antimony trichloride and silver perchlorate the dioxane molecule is reorienting about the O-O axis at 298°K but is rigid at 77°K. Rotation of the benzene ring at 25°C in the complex AgClO₄.C₆H₆ suggests that the reported distortion of the benzene ring may be incorrect. At low temperatures the agreement between the theoretical and and experimental second moments shows that the essential features of the structure are correct. The implication of the infra-red studies of other workers are discussed. Reorientation of both aromatic rings in the complex of benzene and hexafluorobenzene occurs down to low temperatures. The potential barrier hindering rotation of the hexafluorobenzene molecule is estimated to be 1.1 kcal/mole. / Science, Faculty of / Chemistry, Department of / Graduate