Polarized Xenon Production: Multi-liter Accumulation

Hyperpolarized gases, both xenon-129 and helium-3, have demonstrated utility in structural and functional lung imaging and quantifying lung disease. In contrast to helium-3, however, xenon is cheap and abundant. Its lower diffusion constant offers scientific advantages over helium, offsetting the disadvantage of its lower gyromagnetic ratio. Availability of a polarizer producing six liters per hour (a liter every ten minutes) at 50% polarization, almost a factor of one-hundred over most existing polarizers, would trigger widespread investigations and applications of hyperpolarized xenon as an imaging agent. The UNH group demonstrated a new type of xenon polarizer that flows the gas mixture at relatively high velocity and low pressure along a direction opposite to the laser beam. This polarizer demonstrated polarization of over 60% for small quantities and 20% for a production rate of over four liters per hour. The figure-of-merit (polarization times production rate) of this polarizer presently exceeds all other polarizer technologies by an order of magnitude. We propose to increase the output by another factor of six to ten. The cryogenic technology routinely used to accumulate hyperpolarized xenon recovers only 60% to 80% of the produced polarization for a fraction of a liter and far less for larger accumulations. Our new technique proposed for Phase I STTR successfully demonstrated 100% recovery for one-half liter and 88% recovery for one liter. We fabricated a prototype freeze-out cell, implemented an automated moving cryostat, and tested the device on our existing polarizer. Furthermore, we solved the critical materials question to produce a scalable implementation. Simple extensions of this implementation offer accumulation and full recovery of virtually unlimited quantities of hyperpolarized xenon. In Phase II we propose to increase the capacity of the accumulator, improve the control hardware and software, and simplify and automate the thawing procedure. We also comprehensively address the remaining limitations to scaling up the entire polarizer: polarizer column glassware design, gas flow parameters, and vacuum capacity. Increasing laser output and reducing the physical size of the polarizer are separately funded STTRs. These combined developments will scale up our laboratory prototype and convert it to a practical commercially-available hospital-based device.