New xenon gas polarizer with application to magnetic resonance imaging.

摘要

This thesis describes the development and construction of a new xenon gas polarizer. The main motivation was to investigate methods to increase the xenon polarization and to promote its application in magnetic resonance imaging (MRI) and other biomedical research.; The polarizer is based on the technique of spin-exchange optical pumping. Laser polarized xenon gas is accumulated in a separate liquid nitrogen cold bath. At the end, the xenon ice is thawed-out and applied for animal or human lung imaging.; Two nuclear magnetic resonance (NMR) instruments were built to monitor xenon polarizations. Both water (1H) and enriched 129 Xe phantoms were used for calibration.; The laser system developed for the polarizer used two high-power diode laser arrays. External-cavity line-narrowing technology was used to provide a narrow-spectrum and cost-effective light source. The full-width-half-maximum of the laser spectrum was narrowed from 2-3 nm to 0.2 nm. A new configuration of the laser-diode arrays involving orthogonal orientation was developed to increase the beam power and homogeneity. Two-axis beam-shaping optics was also developed to couple the light to the glass polarization chamber efficiently.; The polarizer system was built inside and around a 10120 gauss superconducting magnet to reduce the gaseous and solid xenon relaxation and to provide a single homogeneous field for all aspects of the polarization process. Static spin-exchange optical pumping reached a high level of more than 87% polarization.; We investigated the magnetic field effect on the spin-exchange rate constant with real-time NMR measurements. Furthermore, the pumping chamber was placed at a position with lower magnetic field for control experiments. We found that even at our cell gas composition of xenon 37 torr, nitrogen 365 torr, and helium 3247 torr, the residual van der Waals spin-exchange interaction could not be ignored. The 10120 gauss field apparently quenched this helpful process.; The polarized xenon gas was applied to a xenon gas diffusion coefficient study and also to several rabbit lung MRI imaging studies. Highest thawed-out xenon polarization was 17.9%.; The work described in this thesis provided data and findings helpful for the future design of advanced, cost-effective and easy maintenance xenon gas polarizer.