Hyperpolarized gases, both xenon-129 and helium-3, have demonstrated their 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 compact, robust, commercial polarizer producing 50% polarization in useful quantities for human imaging 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 4 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. Separate STTR projects to increase the useable laser power and to the cryogenic accumulation capacity would increase the polarizer output by another factor of 6 to 10. The polarization technology relies on a long polarization column immersed in a uniform 25 gauss field, an NMR region with adjustable field having 100 ppm uniformity, and a very strong field accumulation region. The interaction of these elements must be eliminated to make the system compact. Our Phase 1 STTR project included numerical simulation of novel asymmetric permeability structures to transport, shape, and spread magnetic field lines creating uniform field volumes and smooth transitions between regions. It also included fabrication of prototypes and measurements confirming the agreement between simulation and realization. We completed several hundred design calculations and fabricated and characterized 2 prototypes, meeting the design critera. In Phase II we propose to further refine the design for improved performance, intergrate the polarizer components into their new magnetic environment, and engineer for ease of access to internal components particularly the final hyperpolarized xenon product. These developments will convert our large laboratory prototype into a practical compact commercially-available hospital-based device.
| Hersman, F William; Ruset, Iulian C; Ketel, Stephen et al. (2008) Large production system for hyperpolarized 129Xe for human lung imaging studies. Acad Radiol 15:683-92 |
