Optimize Counter-Flowing Polarized Xenon Production

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DESCRIPTION (provided by applicant): Decades of refinement of helium-3 polarization technology, funded through the basic physics community, provides the technical foundation for many recent developments in hyperpolarized gas MRI. Noninvasive measurements of lung macro- and micro-structure, ventilation, and local alveolar oxygen concentrations have been recently achieved with helium-3. In contrast, the physics community has directed comparatively little effort towards the challenge of producing hyperpolarized xenon. Consequently, hyperpolarized xenon is presently available to the imaging research community in quantities much less than one liter with polarizations typically below 10%, in most cases substantially below. Full exploitation of the imaging modalities offered by the unique properties of xenon, its low diffusion constant, high solubility, and signature chemical shift, await improved methods of hyperpolarized xenon production. The NHLBI provided R21 funding to the UNH Nuclear Physics Group to demonstrate our innovative concept for polarizing xenon with gas flowing opposite to the laser propagation direction. We developed a computer simulation of the polarization process and its dependence on laser power, gas mixture, flow rate, and temperature. The study revealed a radically new pressure-temperature regime that could increase the xenon polarizer figure-of-merit by a factor of ten to one-hundred. We then implemented a new set of interrelated technologies to enable operation in this new regime. Recent tests confirm world-class performance, yielding polarization percentage in the mid-thirties at flow rates over one-liter-per-hour. Diagnostics indicate production can still be increased by a factor of several at even higher polarization. We propose here a three-part experimental program including 1) measurement of key intrinsic parameters that govern the polarization process, 2) extraction of polarization rates and diagnostic constants, and interpretation of these measurements using our numerical simulation of the polarization process, and 3) optimization of the operating conditions and physical geometry of the polarizer. A separate aspect of our research program, utilization of the xenon for imaging at the Brigham and Women's Hospital, was proposed by members of our collaboration during the fall 2002.