NSF Award
9876741
Award Abstract 9876741<br/>Mitch Albert<br/><br/>The objective of this project is to develop the instrumentation necessary to routinely apply the novel technique of hyperpolarized 129Xe (HypX) magnetic resonance imaging (MRI) and spectroscopy (MRS) to biological investigations conducted in vitro and in vivo. No adequate instrumentation is readily available for producing the multi-liter quantities necessary for such investigations.<br/>Hyperpolarized noble gas magnetic resonance studies may illuminate biological structures and functions that have proved difficult for conventional MR techniques. Magnetic resonance imaging usually employs the strong signal from water protons, abundant in the organism, but the contrast is often low. Moreover, proton-based techniques have shortcomings in some of the most interesting biological environments, notable the lungs and lipid parts of nerves and the brain. 129Xe is extremely soluble in lipids and has a spin-1/2 nucleus of moderate MR delectability, but is virtually undetectable at the concentrations attainable in living organisms. Hyperpolarization of 129Xe ex vivo by spin exchange with optically bumped Rb vapor can enhance its delectability by about a hundred thousand times. The long relaxation time of dissolved hyperpolarized xenon in circulating blood, comparable to the circuit time, suggests that inbreathed, hyperpolarized 129Xe can be used as a magnetic resonance probe of distal tissues. Using hyperpolarized 129Xe, the first images of the gas space in excised mouse lungs have been obtained and the technique has been extended to images of the gas space in living animals. Eventually, the solubility of 129Xe in lipids may permit direct imaging of the perfusion of lipid rich tissues such as the white matter of brain, currently inaccessible to any form of MRI.<br/>To date, HypX-MRI experiments reported in the literature suffer from relatively small volumes and low polarizations. The work funded by this award hopes to make HypX-MRI routine by developing a stable, high-power diode-laser driven optical pumping apparatus to produce liter quantities of hyperpolarized 129Xe. The major components of this apparatus will include (a) an optical pumping chamber optimized for large HypX gas production rates, (b) a gas delivery system for administration of HypX to the subject, (c) a low temperature trap for removal of Rb vapor, and (d) a cryogenic storage system. The system performance will be optimized by systematic studies of optical pumping through modeling and computer simulations, design of novel pumping cells and laser delivery systems, and monitoring and mapping the spatial distribution of the polarization. The modular nature of the instrument will allow us to utilize improved light sources and new concepts.
