from the air we breathe
MagniXene™ production on the XeBox-E10 hyperpolarizer
Xemed announced in May 2007 at the Berlin ISMRM meeting that our model XeBox-E platform would become commercially available beginning in spring 2009 (orders in summer 2008). The core of this system is a finned copper polarizing column consisting of three regions for rubidium saturation, xenon polarization, and rubidium extraction. The cross section of the main 15cm x 15cm column is subdivided into16 polarizing cells. Heat transfer from the gas is facilitated by close proximity of copper dividers. The system is immersed in an oil recirculation system which thermally stabilizes the system and provides precisely controlled rubidium density from the saturator helix. Rubidium is extracted from the flowing gases in the presence of the laser using a water-cooled 30cm extension of the column.
Flowing gases are illuminated by one kilowatt of circularly polarized laser light. Two twelve-bar stacks of hundred watt bars are locked to 795nm with an external cavity tuned by a grating in Littrow configuration. A matrix of optical paths reconfigures the beam to provide an illumination pattern matched to the column geometry. The temperature of the system is controlled by a stainless steel water-to-water heat exchanger coupled to the chilled water supply of the hospital, minimizing the environmental impact of noise and heat load. Safety interlocks protect both equipment and personnel.
Hyperpolarized xenon is extracted from the flowing gases using our novel rising-dewar cryogenic accumulation system. By slowly raising the level of the dewar, the system distributes the location where the xenon is extracted from the downward flowing gases and frozen to the walls of the heat exchanger. The high surface area and low volume of our design provides nearly instantaneous thawing and low losses of both polarization and gas. MagniXene™ output by the system is automatically transferred to a Tedlar bag for medical diagnostic applications.
MagniXene™ polarization is measured both during production and after thawing by our calibrated on-board NMR system. The NMR system offers two-field capability allowing precise and routine calibration with water for quality assurance.
Performance
The XeBox-E10 prototype platform has been demonstrated to provide MagniXene™ at a production rate of 10 liters/hour at typical polarizations of 50%. Its accumulation system is capable of accumulating a two liter bolus without significant freeze-thaw losses. Its NMR system provides polarization measurements with absolute accuracy better than 10% and stability of better than 5%. Operation of the commercial version will be automated through control software. Data on performance, diagnostics, and various safety parameters will be recorded and archived.
