Optimize Counter-Flowing Polarized Xenon Production

描述（由申请人提供）： 几十年来，基础物理学界资助的氦-3极化技术的改进为超极化气体MRI的许多最新发展提供了技术基础。肺的宏观和微观结构，通气量和局部肺泡氧浓度的非侵入性测量最近已实现与氦-3。相比之下，物理学界对产生超极化氙的挑战所做的努力相对较少。因此，超极化氙目前可用于成像研究界，其量远小于1升，极化通常低于10%，在大多数情况下基本上低于10%。氙的独特性质，其低扩散常数，高溶解度和签名化学位移提供的成像方式的充分利用，等待改进的超极化氙生产方法。NHLBI向UNH核物理组提供了R21资金，以展示我们的创新概念，即用与激光传播方向相反的气体来极化氙气。我们开发了一个计算机模拟的偏振过程及其依赖于激光功率，气体混合物，流量和温度。这项研究揭示了一种全新的压力-温度机制，可以将氙偏振器的品质因数提高10到100倍。然后，我们实施了一套新的相互关联的技术，以实现在这一新制度下的运作。最近的测试证实了世界级的性能，在流量超过每小时一升的情况下，在三十年代中期产生极化百分比。诊断表明，在更高的极化下，产量仍然可以增加几倍。我们在这里提出了一个由三部分组成的实验方案，包括1）测量的关键内在参数，支配的偏振过程，2）提取的偏振速率和诊断常数，并解释这些测量使用我们的数值模拟的偏振过程，和3）优化的操作条件和物理几何的偏振器。我们的研究计划的一个单独的方面，利用氙成像在布里格姆妇女医院，提出了我们的合作成员在2002年秋季。

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.