This thesis deals with the synthesis of dendritic gadolinium complexes based on DOTA, with a view to obtaining enhanced relaxivities. Li addition to the inherently long electronic relaxation time and high paramagnetic moment of the gadolinium (III) ion, the speed of rotation of its complexes in solution is a decisive parameter in the determination of the relaxivity. This parameter is dependent on the molecular mass of the complex. Initially, the enantioselective synthesis of novel a-substituted analogues of DOTA was attempted but was not successful due to difficulties encountered in attaining the tetraalkylation of cyclen and the purification of the products obtained. Therefore, further studies were carried out based on the known [Gd(gDOTA)]" system. The synthesis of three medium M(_W) dendrons, each with a focal primary amino group was carried out. Their structures may be described as dendrimeric analogues of poly(ethylene glycol). Two of these structures were successfully coupled to the gadolinium (III) chelate, [Gd.gDOTA]. The acid-catalysed epimerisation of the statistical distribution of stereoisomers yielded solely the (RRRR)/(SSSS) isomeric pair. This system had previously been shown to undergo fast water exchange. The coupling and deprotection procedure yielded paramagnetic dendritic complexes with molecular weights of 2013 and 3535.Relaxivity measurements were carried out on these systems and the results showed significantly higher relaxivities of 18 and 21 mM(^-1) s(^-1) respectively, compared with a value of 7.8 mM(^-1) s(^-1) for the parent compound. Examination of NMRD profiles for the larger system showed a decrease in the rotational correlation time to 310 ps at 298 K, as expected. However, this was accompanied by an increase in the inner-sphere water exchange lifetime to 570 ns at 298 K. Therefore, although an improvement in relaxivity was obtained through a coupling to the slower rotation of the system in solution, this enhancement was limited by the accompanying decrease in the rate of water exchange. The best fitting procedure of the NMRD profiling procedure revealed the presence of 8 second-sphere water molecules at an average distance of 4Å. The second sphere contribution was shown to be the dominant contributor to the overall relaxivity. This accounted for >50% of the increased relaxivity.

Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 100-103.

No description available.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

The major work involved is the debugging procedure on the Varian Model V-21003 electromagnet, power supply and spectrometer and the design and construction of supporting structure to house the various pieces of apparatus which were required to complete the system.Equipment which was not immediately available was then designed and constructed, with the final step being the testing. of the entire system for its integrity.Adjustments to each component was then carried out to obtain the best signal possible, noting the various changes caused by the condition and setting of each section of the system.

This thesis comprises a computer analysis of NMR-determined interatomic distance in strontium formate dihydrate. The computer program is designed to locate the hydrogen atoms associated with the water molecules in strontium formate dihydrate. The bond length of the oxygen-hydrogen bond is assumed to be fixed. The program varies the hydrogen separation, plotting total proton interaction against the hydrogen separation distance. Using Van Vleck's second moment theory, the hydrogen-hydrogen distances were determined.. The value of the second moment of the NMR absorption curve is 24.6 gauss2, obtained from investigation by Dr. D. E. Koltenbah. The result of this thesis is that the proton separation is 1.47± .02 A. This result is found to be close enough to other studies to conclude that the program analysis is essentially sound.

Multidimensional nuclear magnetic resonance (NMR) spectroscopy has become one of the most important techniques available for studying the structure and function of biological macromolecules at atomic resolution. The conventional approach to multidimensional NMR involves the sampling of the time domain on a Cartesian grid followed by a multidimensional Fourier transform (FT). While this approach yields high quality spectra, as the number of dimensions is increased the time needed for sampling on a Cartesian grid increases exponentially, making it impractical to record 4-D spectra at high resolution and impossible to record 5-D spectra at all. This thesis describes new approaches to data collection and processing that make it possible to obtain spectra at higher resolution and/or with a higher dimensionality than was previously feasible with the conventional method. The central focus of this work has been the sampling of the time domain along radial spokes, which was recently introduced into the NMR community. If each radial spoke is processed by an FT with respect to radius, a set of projections of the higher-dimensional spectrum are obtained. Full spectra at high resolution can be generated from these projections via tomographic reconstruction. We generalized the lower-value reconstruction algorithm from the literature, and later integrated it with the backprojection algorithm in a hybrid reconstruction method. These methods permit the reconstruction of accurate 4-D and 5- D spectra at very high resolution, from only a small number of projections, as we demonstrated in the reconstruction of 4-D and 5-D sequential assignment spectra on small and large proteins. For nuclear Overhauser spectroscopy (NOESY), used to measure interproton distances in proteins, one requires quantitative reconstructions. We have successfully obtained these using filtered backprojection, which we found was equivalent to processing the radially sampled data by a polar FT. All of these methods represent significant gains in data collection efficiency over conventional approaches. The polar FT interpretation suggested that the problem could be analyzed using FT theory, to design even more efficient methods. We have developed a new approach to sampling, using concentric rings of sampling points, which represents a further improvement in efficiency and sensitivity over radial sampling. / Dissertation

In Magnetic Resonance Imaging, the time required to generate an image is proportional to the number of steps used to encode the spatial information. In rapid imaging, an array of coil elements and receivers are used to reduce the number of encoding steps required to generate an image. This is done using knowledge of the spatial sensitivity of the array and receiver channels. Recently, these arrays have begun to include a large number of coil elements. Ideally, each coil element would have its own receiver channel to acquire the image data. In practice, this is not always possible due to economic or other constraints. In this dissertation, methods are explored to combine a large array to a limited number of receivers so as to optimize the performance for parallel imaging; this dissertation focuses on SENSE in particular. Simple combinations that represent larger coils that might be constructed are discussed. More complex solutions form current sheets. One solution uses Roemer'€™s method to optimize image SNR at a set of points. In this dissertation, Roemer's solution is generalized to give the weighting coefficients that optimize SNR over regions. Also, solutions fitted to ideal profiles that minimize noise amplification are shown. These fitted profiles can allow the SENSE algorithm to function at optimal reduction factors. Finally, a description of how to build the combiner in hardware is discussed.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 89-90).

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.