Large Volume Production of Hyperpolarized Noble Gas for Biological Magnetic Resonance Research

这个项目的目标是开发必要的仪器，将超极化129Xe(HypX)磁共振成像(MRI)和光谱分析(MRS)这一新技术常规应用于体外和体内的生物学研究。目前还没有足够的仪器来生产这类研究所需的多升容量。超极化稀有气体磁共振研究可能会阐明常规磁共振技术难以解释的生物结构和功能。磁共振成像通常使用来自水质子的强烈信号，这种信号在生物体中含量丰富，但对比度往往很低。此外，基于质子的技术在一些最有趣的生物环境中也存在缺陷，尤其是肺、神经和大脑的脂肪部分。129Xe极易溶于脂类，有一个自旋为1/2的原子核，具有中等的MR快乐性，但在活体中可获得的浓度下几乎无法检测到。利用光学碰撞Rb蒸气与~(129)Xe进行自旋交换，使~(129)Xe在体外超极化，使其可乐性提高约10万倍。循环血液中溶解的超极化氙弛豫时间较长，与循环时间相当，提示吸气式超极化129Xe可用作远端组织的磁共振探头。利用超极化的129Xe，首次获得了小鼠离体肺气体空间的图像，并将该技术扩展到了活体动物的气体空间图像。最终，129Xe在脂类中的溶解性可能使富脂组织(如脑白质)的血流灌注直接成像，目前任何形式的MRI都无法获得这些组织的灌注。到目前为止，文献中报道的HypX-MRI实验的体积相对较小，极化较低。这项由该奖项资助的工作希望通过开发一种稳定的、高功率二极管激光驱动的光学泵浦设备来产生少量超极化的129Xe，从而使HypX-MRI成为常规。该装置的主要部件将包括：(A)为大的HypX气体产生率优化的光学泵浦室；(B)用于给受试者注射HypX的气体输送系统；(C)用于去除Rb蒸气的低温疏水器；以及(D)低温储存系统。通过建模和计算机模拟对光学泵浦进行系统研究，设计新型泵浦单元和激光传输系统，以及监测和绘制偏振的空间分布，将优化系统的性能。该仪器的模块化性质将使我们能够利用改进的光源和新的概念。

Award Abstract 9876741Mitch AlbertThe objective of this project is to develop the instrumentation necessary to routinely apply the novel technique of hyperpolarized 129Xe (HypX) magnetic resonance imaging (MRI) and spectroscopy (MRS) to biological investigations conducted in vitro and in vivo. No adequate instrumentation is readily available for producing the multi-liter quantities necessary for such investigations.Hyperpolarized noble gas magnetic resonance studies may illuminate biological structures and functions that have proved difficult for conventional MR techniques. Magnetic resonance imaging usually employs the strong signal from water protons, abundant in the organism, but the contrast is often low. Moreover, proton-based techniques have shortcomings in some of the most interesting biological environments, notable the lungs and lipid parts of nerves and the brain. 129Xe is extremely soluble in lipids and has a spin-1/2 nucleus of moderate MR delectability, but is virtually undetectable at the concentrations attainable in living organisms. Hyperpolarization of 129Xe ex vivo by spin exchange with optically bumped Rb vapor can enhance its delectability by about a hundred thousand times. The long relaxation time of dissolved hyperpolarized xenon in circulating blood, comparable to the circuit time, suggests that inbreathed, hyperpolarized 129Xe can be used as a magnetic resonance probe of distal tissues. Using hyperpolarized 129Xe, the first images of the gas space in excised mouse lungs have been obtained and the technique has been extended to images of the gas space in living animals. Eventually, the solubility of 129Xe in lipids may permit direct imaging of the perfusion of lipid rich tissues such as the white matter of brain, currently inaccessible to any form of MRI.To date, HypX-MRI experiments reported in the literature suffer from relatively small volumes and low polarizations. The work funded by this award hopes to make HypX-MRI routine by developing a stable, high-power diode-laser driven optical pumping apparatus to produce liter quantities of hyperpolarized 129Xe. The major components of this apparatus will include (a) an optical pumping chamber optimized for large HypX gas production rates, (b) a gas delivery system for administration of HypX to the subject, (c) a low temperature trap for removal of Rb vapor, and (d) a cryogenic storage system. The system performance will be optimized by systematic studies of optical pumping through modeling and computer simulations, design of novel pumping cells and laser delivery systems, and monitoring and mapping the spatial distribution of the polarization. The modular nature of the instrument will allow us to utilize improved light sources and new concepts.