Optimize Counter-Flowing Polarized Xenon Production

描述(由申请人提供)： 几十年来，由基础物理界资助的氦-3偏振技术的改进，为超极化气体磁共振成像的许多最新发展提供了技术基础。最近用氦-3实现了对肺宏观和微观结构、通风和局部肺泡氧浓度的非侵入性测量。相比之下，物理学界对产生超极化氙气的挑战相对较少。因此，目前成像研究界可以获得的超极化氙气的数量远远不到一升，极化程度通常低于10%，在大多数情况下大大低于10%。充分利用氙气独特的性质所提供的成像方式，即低扩散常数、高溶解度和标志性的化学位移，等待超极化氙气生产的改进方法。NHLBI向UNH核物理小组提供了R21资金，以展示我们的创新概念，即在气体流动与激光传播方向相反的情况下极化氙气。我们开发了偏振过程的计算机模拟，以及它与激光功率、混合气体、流速和温度的关系。这项研究揭示了一种全新的压力-温度制度，它可能会使氙气偏振片的品质因数增加10到100倍。然后，我们实施了一套新的相互关联的技术，使其能够在这一新制度下运行。最近的测试证实了世界级的性能，在每小时一升以上的流速下，产生的极化百分比在35%左右。诊断表明，即使在更高的极化条件下，产量仍可提高数倍。我们提出了一个由三部分组成的实验方案，包括1)测量控制偏振过程的关键内在参数，2)提取偏振率和诊断常数，并用我们对偏振过程的数值模拟来解释这些测量结果，以及3)优化偏振器的操作条件和物理几何。我们研究计划的另一个方面，在布里格姆妇女医院利用氙气进行成像，是由我们的合作成员在2002年秋季提出的。

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.