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

该项目的目的是开发必要的仪器，以常规应用超极化129Xe （HypX）磁共振成像（MRI）和光谱（MRS）的新技术进行体外和体内的生物研究。没有足够的仪器可以随时用于生产这种调查所需的多升数量。超极化惰性气体磁共振研究可以阐明传统磁共振技术难以揭示的生物结构和功能。磁共振成像通常利用生物体中丰富的水质子发出的强信号，但对比度通常很低。此外，基于质子的技术在一些最有趣的生物环境中有缺点，特别是在肺和神经和大脑的脂质部分。129Xe极易溶于脂质，具有中等MR可降解性的自旋1/2核，但在活生物体中几乎无法检测到可达到的浓度。通过与Rb蒸气的自旋交换，使129Xe的超偏振性提高了10万倍左右。溶解的超极化氙在循环血液中的弛豫时间较长，与回路时间相当，提示吸入的超极化129Xe可作为远端组织的磁共振探头。利用超偏振129Xe，获得了切除小鼠肺部气体空间的第一张图像，并将该技术扩展到活体动物的气体空间图像。最终，129Xe在脂质中的溶解度可能允许直接成像富脂组织的灌注，如脑白质，目前无法通过任何形式的MRI。迄今为止，文献中报道的HypX-MRI实验存在相对较小的体积和低极化。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泵浦装置来产生升量的超偏振129Xe，使HypX-MRI成为常规。该装置的主要组成部分将包括(a)针对大HypX气体生产速率优化的光泵腔，(b)用于向受试者输送HypX的气体输送系统，(c)用于去除Rb蒸气的低温陷阱，以及(d)低温储存系统。系统研究光泵浦的建模和计算机模拟，设计新型泵浦单元和激光传输系统，监测和绘制偏振的空间分布，从而优化系统性能。该仪器的模块化特性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.