Development of a spin polarized noble gas generator for sensitivity enhanced xenon-129 nuclear magnetic resonance spectroscopy and imaging.

摘要

Xenon-129 NMR has long been used as a sensitive surface probe for microporous systems such as clathrates, zeolites, proteins, and catalysts. However, this technique is hindered by the low signal intensity of xenon due to its small thermal polarization (approximately 10-5 at 9.4 T). The advent of spin-exchange optical pumping has enabled the production of xenon-129 with a nuclear polarization 4--5 orders of magnitude greater than the Boltzmann equilibrium value. This has led to new NMR applications such as medical imaging of lungs and signal enhancement of other nuclear species by polarization transfer or thermal mixing. The increasing number of NMR and MRI applications requiring large volumes of highly spin-polarized xenon-129 or helium-3 gas has placed new demands on spin-exchange optical pumping (SEOP) systems.;The advent of high power (>30 W) laser diode array (LDA) systems with wavelengths in the near infrared has led to significant increases in the quantity and rate of production of spin-polarized helium-3 and xenon-129 gasses.;This work reports the development and evaluation of a continuous flow SEOP system incorporating a 210 W diode array laser system with a 1.7 nm (950 GHz) spectral width. Experimental data detailing the absolute xenon-129 nuclear polarization and bulk magnetization production dependence on certain operating parameters such as gas flow rate, gas composition, and magnetic field strength are presented. In addition, this system provides a unique opportunity to study the SEOP performance as a function of laser power up to an unprecedented 210 W. While nuclear polarization has been the performance benchmark of polarized noble gas generators, in many applications, it is the bulk magnetization produced per unit time that is of greater relevance.;Finally, results demonstrating the ability to produce xenon-129 with a nuclear spin-polarization of >40%, as well as the ability to produce spin-polarized xenon-129 for imaging and spectroscopic applications, are presented. The ability of the polarizer to produce polarized 129Xe gas is unmatched by any other polarizer currently described in the literature.