<p> Hemodialysis vascular access, the interface between a dialysis patient and a dialysis machine, is quite literally the lifeblood of a patient's health. Vascular access dysfunction is the leading cause of hospitalization in hemodialysis patients. The occlusive growth of neointimal hyperplasia (NH) in expanded polytetrafluoroethylene (ePTFE) ringed grafts is the primary cause of failure. To further develop a proposed thermal ultrasound treatment to reduce or prevent NH in arteriovenous vascular grafts, the acoustic properties of ePTFE were studied in water and alcohol solutions. Previous reports of ePTFE acoustic properties are critiqued. It was found that the acoustic transmission and attenuation through ePTFE, and therefore the potential for an ultrasound-based therapy for NH, are heavily dependent on the medium in which the graft is immersed, suggesting that the acoustic properties of implanted grafts will change as grafts mature in vivo. The acoustic impedance and attenuation of water-soaked ePTFE were 0.478 &plusmn; 1.43 &times; 10^-2 MRayl and 1.78 &plusmn; 0.111 Np/cm*MHz, respectively, while the acoustic impedance and attenuation of ePTFE in alcohol were 1.49 &plusmn; 0.149 MRayl and 0.77 &plusmn; 1.1 &times; 10^-2 Np/cm*MHz, respectively. The use of focused ultrasound to heat implanted ringed ePTFE grafts was numerically modeled from 1.35- and 1.443-MHz transducers for in vitro geometries. Power deposition and heating, in turn, differed by an order of magnitude between various graft acoustic properties. Graft rings were predicted to be substantial absorbing and scattering features. In vitro phantom models were constructed: one with and one without thermocouples. At 1 W of acoustic power, the maximum temperature rise was 8&ring; C. The thermocouple model containing a water-soaked graft did not experience heating in the far graft wall. The MRTI model confirmed that the graft rings are an absorbing/scattering feature. Heating was not prevented in the presence of water flow through the graft. Water was not heated significantly. Overall, results suggest ultrasound exposure can be used to generate temperature rises corresponding with the potential prevention or inhibition of NH in ringed ePTFE vascular grafts. A hybrid therapeutic/diagnostic transducer design with a therapeutic semi-annular array surrounding a diagnostic linear array is presented. Compared to a solid transducer of the same dimensions, there were only marginal aberrations in the focal plane. Numerical optimization of the element drive configuration indicated that the least distorted focal plane was produced by uniform phase and magnitude at each element.</p>

A novel version of the CSA (Chemical Shift Anisotropy) amplification experiment which results in large amplification factors is introduced. Large xa (up to 48) are achieved by sequences which are efficient in terms of the number of π pulses and total duration compared to a modification due to Orr et al. (2005), and greater flexibility in terms of the choice of amplification factor is possible than in our most recent version. Furthermore, the incorporation of XiX decoupling ensures the overall sensitivity of the experiment is optimal. This advantage has been proved by extracting the CSA tensors for a novel vinylphosphonate-linked nucleotide. The application of CSA amplification experiment to six nucleosides is also discussed. The measured principal tensor values are compared with those calculated using the recently developed first-principles methods. Throughout this work, the NMR parameters of all nucleosides are presented. Finally, high-resolution multi-nuclear solid-state NMR experiments are used to study some novel vinyl phosphonate-linked oligo-nucleotides.

The overall aim of this work was to develop MRI methods and techniques to study the physiology and the pathology of the gastrointestinal tract, with particular attention to the colon. Besides, the development of new methods was aimed in order to perform quantitative analysis using proton and fluorine MRI. In particular the first experimental chapter describes the development and the optimisation of imaging protocols for studying colonic function in undisturbed physiologically relevant conditions. In addition a texture analysis method based on Gabor filters is developed and used for the objective assessment of colonic content characteristics. The mechanisms of action of common anti-diarrhoeal and anti-constipation agents are also investigated. The last experimental chapter describes the development of methods for using markers to measure GI transit. Transit time, i.e. the time it takes for a marker to pass through the entire gut, is often affected by functional gastrointestinal disorders, therefore it is of primary importance to develop a non-invasive and effective technique for the diagnosis of such gastrointestinal diseases. The use of fluorinated agents and its many advantages compared to other techniques is outlined and the first in vivo studies at high field are presented. The use of gadolinium based compounds as an additional marker is also discussed.

The work described in this thesis was carried out at the Sir Peter Mansfield Magnetic Resonance Centre at the University of Nottingham between March 2006 and December 2009. All work described in this thesis was performed by the author, except where indicated. This thesis aims to develop and implement ASL techniques to measure haemodynamic responses to neural activity. The development of a new technique Double Acquisition Background Suppression (DABS) is presented as a remedy for a newly discovered artefact affecting Philips Achieva 7 T scanners and other sources of variation in baseline signals such as physiological noise. The new technique (DABS) was developed for simultaneous acquisition of ASL (with suppressed static tissue signal) and BOLD data using the FAIR scheme. This method not only provided a solution to obtaining ASL data at 7 T, despite the Roman Artefact, but also proved to reduce the contribution of physiological noise to ASL images, which is problematic, especially at ultra-high magnetic field strengths. The statistical verification was carried out based on the neural activation induced by a finger-tapping stimulus. A simplified model for quantifying CBVa.with the Look-Locker sampling method is proposed in this thesis to overcome the need for the Step-wise Compartmental Model (SCM). The Look-Locker sampling scheme acquires multiple readout pulses following the labelling and provides an estimation of transit time as well as CBVa. Here the simplified model is used to assess changes due to visual stimulation and validated against the SCM model. The application of LL-FAIR to form CBF and CBVa weighted data with improved SNR compared to traditional single TI FAIR technique is then shown. This method uses a summation over LL-EPI readout pulses and is used to asses the temporal characteristics and absolute changes in CBF and CBVa haemodynamic responses to a short (4.8 s) and long (9.6 s) visual stimulus. LL-FAIR methods are then used to appraise the neural coupling of haemodynamic parameters and assess Grubb's relationship. CBF and CBVa. Data were collected together with CBVtot data from a bolus injection of contrast agent. Assessing Grubb's power-law (CBVtot = CBFCI:)for neuronal activation, which was originally derived in primates during a steady state response of hypercapnia, a was found in this human study to be between 0.22 ± 0.08 and 0.29, dependent on the analysis method. In addition, the power-law relationship between CBVtot and CBVa.was assessed, and resulted in a similar relation, yielding aTA = 0.42 ± 0.14 and 0.40. Since CBF is thought to be driven by CBVa.the power-law between these parameters was also tested with a value of aFA = 1.35 ± 0.64 and 1.21, found in close agreement with earlier animal work.

This thesis presents the application of diffusion weighted imaging (DWI) and relaxometry MRI studies in three organs in the abdomen, the kidney, colon and liver. These methods are first applied at 1.5 Tesla in healthy volunteers and patients with Cardiorenal Syndrome (CRS), a clinical condition in which cardiac and renal dysfunctions (RD) coexist. Diffusion parameters are determined using the mono-exponential ADC, bi-exponential IVIM, stretched-exponential and Kurtosis models, as well as diffusion tensor imaging (DTI) in order to assess pathophysiology and structural changes in the kidney. Complementary longitudinal relaxation time (T1) mapping and PC-MRI flow measures are collected for comparison with diffusion parameters. The assessment of the colonic content using T1 measures as a biomarker of water absorption and health is presented in the second study. The main objective of the study was to determine the robustness of bi-exponential model in the fitting of T1 in the colonic contents of ascending colon. T1 measurements of colonic content are made at different positions in the ascending colon, before and after a liquid challenge. The reliability of T1 measurements of colonic content were compared across observers. The heterogeneity in the measurements was evaluated by considering different ROI sizes and locations. The final study is the assessment of liver function associated with Chronic Liver Disease (CLD) using DWI and T1 measurement at 1.5 T and a comparison with histological measures. the Measurements of T1 and diffusion parameters (ADC and IVIM) to stratify fibrosis stage in liver disease are combined with T2* measurement of iron accumulation. The repeatability and reproducibility of this protocol is then tested in the healthy liver using MRI at 3T for the assessment of structural and haemodynamic changes for future studies, with an evaluation of the choice of b-values to inform fitting of the bi-exponential (IVIM) model provided.

The general aim of the work detailed in this thesis is to improve the quality of electroencepholography (EEG) recordings acquired simultaneously with functional magnetic resonance imaging (fMRI) data. Simultaneous EEG-fMRI recordings offer significant advantages over the isolated use of each modality for measuring brain function. The high temporal resolution associated with EEG complements the high spatial resolution provided by fMRI. However, combining the two modalities can have significant effects on the overall data quality. The gradient artefact (GA), which is induced on the EEG cables by the time varying magnetic fields associated with fMRI sequences, can be particularly problematic to correct for in experiments containing any subject movement. In this thesis, two novel, movement-invariant methods are introduced for correcting the GA. The first method is named the gradient model fit (GMF) and relies upon the assumption that the GA can be modelled as a linear combination of basis components, where the relative weighting of each component varies dependent upon subject position. By modelling these underlying components, it is possible to characterise and remove the GA, which is particularly beneficial in the presence of subject movement. The second method named the difference model subtraction (DMS) relies on the assumption that the GA varies linearly for small changes in subject position. By modelling the change in GA for a basis set of likely head movements, it was shown to be possible to combine DMS with standard GA correction methods to improve the attenuation of the GA for data acquired during subject movement. Both methods showed a significant improvement over the existing GA correction techniques, particularly for experiments containing subject movement. These methods are therefore relevant to any experimenter interested in working with subject groups such as children or patients where movement is likely to occur.

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Magnetite, Fe3O4, is a strongly electronically correlated system and thus exhibits remarkable electrical and magnetic properties, including the Verwey transition at TV 122 K, which has attracted much attention since its 1939 discovery. Fe3O 4 has recently revealed a new effect. By performing experiments at the nanoscale, we have discovered a novel electric-field driven transition (EFD) in magnetite below TV, from high- to low-resistance states driven by application of high bias. The EFD transition is detected both in Fe3O4 nanoparticles and thin films, is hysteretic in voltage under continuous biasing, and is not caused by self-heating. In this thesis we report on a thorough investigation of this new EFD transition. First, we unveil the origin of hysteresis observed in I-V curves. By applying voltage in a pulsed manner with controlled parameters, we unambiguously demonstrate that while the transition is field-driven, hysteresis results from Joule heating in the low-resistance state. A simple relaxation-time thermal model captures the essentials of the hysteresis mechanism. Second, by doing multilead (four-terminal) electrical measurements, we quantitatively separate the contributions of the Fe3O4 channel and each metal/electrode interface, and explore the contact effects upon testing devices incorporating various contact metals We demonstrate that on the onset of the transition, contact resistances at both source and drain electrodes and the resistance of Fe3O4 channel decrease abruptly. Finally, we measured the distribution of switching voltages, V sw, its evolution with temperature, and its dependence on out-of-plane magnetic field. Based on the experimental facts collected in this work we suggest the possible mechanism of EFD transition in Fe 3O4 as a charge gap closure by electric field. This is one of the first experimental observation of a theoretically predicted EFD transition in correlated insulators. These studies demonstrate that nanoscale, nonequilibrium probes can reveal much about the underlying physics of strongly correlated materials.

Metal-dielectric nanostructures capable of supporting electromagnetic resonances at optical frequencies are the vital component of the emerging technology called plasmonics. Plasmon is the electromagnetic wave confined at the metal-dielectric interface, which may effectively couple to the external electromagnetic excitation with the wavelength much larger than the geometric size of the supporting structure. Plasmonics can improve virtually any electromagnetic technology by providing subwavelength waveguides, field enhancing and concentrating structures, and nanometer size wavelength-selective components. The focus of this work is the fabrication, characterization and modeling for novel plasmonic nanostructures. Effects of the symmetry in plasmonic structures are studied. Symmetric metal nanoparticle clusters have been investigated and show highly tunable plasmon resonances with high sensitivity to the dielectric environment. Efficient, highly-scalable methods for nanoparticle self-assembly and controlled partial submicron metal sphere coatings are developed. These partially Au coated dielectric spheres have shown striking properties such as high tunability, as well as the control on resonant electromagnetic field enhancement and scattering direction. Studied effects are of vital importance for plasmonics applications, which may improve virtually any existing electromagnetic technology. Optical resonances in metal-dielectric nanostructures were correlated with LC circuit resonances elaborating on the resonance tunability, dielectric environment, symmetry breaking and mode coupling (Fano resonance) effects.