Configuration and Performance of a Mobile 129 Xe Polarizer
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Appl Magn Reson (2013) 44:65–80 DOI 10.1007/s00723-012-0425-7
Magnetic Resonance
Configuration and Performance of a Mobile 129 Xe Polarizer Sergey E. Korchak • Wolfgang Kilian Lorenz Mitschang
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Received: 17 August 2012 / Revised: 17 October 2012 / Published online: 10 November 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com
Abstract A stand-alone, self-contained and transportable system for the polarization of 129Xe by spin exchange optical pumping with Rb is described. This mobile polarizer may be operated in batch or continuous flow modes with medium amounts of hyperpolarized 129Xe for spectroscopic or small animal applications. A key element is an online nuclear magnetic resonance module which facilitates continuous monitoring of polarization generation in the pumping cell as well as the calculation of the absolute 129Xe polarization. The performance of the polarizer with respect to the crucial parameters temperature, xenon and nitrogen partial pressures, and the total gas flow is discussed. In batch mode the highest 129Xe polarization of PXe = 40 % was achieved using 0.1 mbar xenon partial pressure. For a xenon flow of 6.5 and 26 mln/min, PXe = 25 % and PXe = 13 % were reached, respectively. The mobile polarizer may be a practical and efficient means to make the applicability of hyperpolarized 129Xe more widespread.
1 Introduction The nuclear spin polarization of noble gases becomes transiently enhanced by four to five orders of magnitude when the angular momentum from laser photons is transferred to the nuclear spins by spin exchange processes with optically pumped alkali metal atoms [1]. Nuclear magnetic resonance (NMR) measurements on such hyperpolarized noble gases are boosted in sensitivity, offering a great potential for spectroscopy and imaging of molecules, materials and organisms [2–4]. Their biocompatibility and the ability and ease to introduce them non-invasively into cell culture, animals, and humans [5, 6] render hyperpolarized noble gases particularly suitable for biomolecular research and clinical applications. Magnetic resonance S. E. Korchak W. Kilian (&) L. Mitschang Physikalisch-Technische Bundesanstalt, Abbestr. 2-12, 10587 Berlin, Germany e-mail: [email protected]
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imaging (MRI) of human lungs has been developed with the focus on 3He [7, 8], because of the isotopic pureness and the high gyromagnetic ratio which lead when combined with effective polarization techniques to the highest achievable magnetization among the noble gases. Nevertheless, a wide variety of applications using hyperpolarized 129Xe are currently explored due to several reasons. Natural xenon is abundant, inexpensive, and, nowadays, isotope enrichment is affordable. The spin1/2 nucleus 129Xe (natural abundance 26 %) can keep the polarization from tens of seconds in solution [9] and in vivo [10] up to 100 h in the gas phase [11]. The polarizability of its electron shell accounts for a millimolar solubility in aqueous solution with che
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