A Compact LHe-Free Fast-Switching-Field MRI Magnet for Ratiometric Molecular Imaging and Novel Contrast Exploration

项目摘要 在这个项目中，我们提出了一种新的磁共振成像(MRI)概念，该概念基于我们创新的FAST- 开关场磁铁设计。我们相信，这种核磁共振磁体将使新的造影剂机制成为可能。 以及用于生物医学研究的比率分子成像。我们将开发和演示一种液氦 (LHe)-无超导磁体，可以在时间上非常迅速地改变磁场，显著不同 场强：中等均匀度的高(3T)场，足以进行弛豫测量和预极化；低场强 (0.5T)用于光谱和成像的高度均匀的场。由此实现的新的对比度机制 磁体包括自旋1/2和四极核之间的能级交叉，加速的自旋-晶格弛豫，以及 绝热退磁-再磁化。通过测量不同场的松弛参数，松弛 可以区分在野外具有不同相对弛豫率的对比度源。这会有帮助的 根据背景量化显像剂浓度或区分显示的单个显像剂的状态 放松行为的环境依赖性变化。超导磁体中的快场变化 可以通过采用最先进的低交流损耗高温超导体(HTS)来实现 温度裕度足够高，以避免淬火。两个场之间的场切换时间将会很快 足以保持极化和弛豫，但对动物和人类都是安全的(&lt；1 S)。我们的其他应用程序 切换磁场可能包括介入性MR和术中手术。在0.5T的磁化率伪影 来自微磁性器件和植入物的，以及来自导电器件的射频加热要少得多。我们相信 随着磁共振波谱和成像技术的进步，图像可以与1.5T相媲美。我们是 相信我们提出的开关场磁共振磁体不仅可以提供新颖的对比剂机制，而且 也是临床前动物甚至人类核磁共振具有竞争力和成本效益的垫脚石 传统的核磁共振磁铁。具体目标是开发一种不含LHe的快速切换场磁共振磁体 通过组合两个HTS磁体-一个2.5-T开关场磁体和一个0.5-T MRI磁体-和 展示快速场切换(高达3T/S)时的MRI场均匀度和稳定性。我们还将表演 具有最佳设计磁场的人体大小的快速切换场磁共振磁体的概念设计。独一无二的 我们的磁体设计的特点是非常低的损耗和在快速切换磁场中的稳定性， 常规低温超导体(LTS)和两个单独工作的HTS的配置 磁体-一个稳定的高度均匀的低场和一个磁场质量适中的快速循环的高场-实现 快速切换功能，性价比高。我们的固体氮气冷却低温系统不 依赖氦，这已经成为一种稀缺和不可靠的商品。这个项目的成功完成将 为更大的--包括人类规模--和更高的磁场铺平道路，使生物医学科学受益。

Project Summary In this project we propose a novel magnetic resonance imaging (MRI) concept based on our innovative fast- switching-field magnet design. We believe that this MRI magnet will make possible new contrast mechanisms and ratiometric molecular imaging for biomedical research. We will develop and demonstrate a liquid-helium (LHe)-free superconducting magnet that can change the field very quickly in time between significantly different field strengths: a high (3T) field of modest-homogeneity adequate for relaxometry and prepolarization; and a low (0.5T) field of high-homogeneity for spectroscopy and imaging. New contrast mechanisms enabled by this magnet include level-crossing between spin 1/2 and quadrupolar nuclei, accelerated spin-lattice relaxation, and adiabatic demagnetization-remagnetization. By measuring relaxation parameters at different fields, relaxation contrast sources that have different relative relaxation rates at the fields could be distinguished. This will help quantify imaging agent concentrations against background or differentiate states of individual agents that exhibit environmentally-dependent changes in relaxation behavior. The fast field change in a superconducting magnet can be achieved by adopting most advanced low-AC-loss high-temperature superconductors (HTS) having a sufficiently high temperature margin to avoid quench. The field switching time between two fields will be rapid enough (<1 s) to retain polarization and relaxometry yet safe for animal and human. Other applications of our switching-field magnet might include interventional MR and intraoperative surgery. At 0.5 T susceptibility artifacts from slightly magnetic devices and implants, and RF heating from conductive devices are much less. We believe the images can be comparable to 1.5 T with progressing MR spectroscopy and imaging technologies. We are convinced that our proposed switching-field MR magnet can not only promise novel contrast mechanisms but also serve as a stepping stone for preclinical animal and even human MRI competitive and cost effective against conventional MRI magnets. The specific aims are to develop a LHe-free fast-switching-field MRI magnet prototype by combining two HTS magnets—a 2.5-T switched-field magnet and a 0.5-T MRI magnet—and demonstrate the MRI field homogeneity and stability during fast field-switching (up to 3 T/s). We will also perform a conceptual design of a human-size fast-switching-field MRI magnet with optimum design fields. The unique features of our magnet design are very low-loss and stable in a fast-switching field, impossible with a conventional low-temperature superconductor (LTS), and configuration of two separately operating HTS magnets—a steady low field of high-homogeneity and a fast-cycling high field of modest-field-quality—to achieve fast-switching feature efficiently in performance and cost. Our solid-nitrogen-cooled cryogenic system does not rely on helium, which has become a scarce and unreliable commodity. Successful completion of this project will pave the way to larger—including human-scale—and higher field magnets, benefitting biomedical sciences.