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，我们提出了一个新的磁共振成像（MRI）的概念，基于我们的创新快速- 开关磁场磁铁设计。我们相信这种磁共振成像磁铁将使新的对比机制成为可能 以及用于生物医学研究的比率分子成像。我们将开发并演示一种液态氦 （LHe）的无超导磁体，其可以在显著不同的时间之间非常快速地改变场。 场强：适度均匀的高（3 T）场，足以进行弛豫测量和预极化; （0.5T）用于光谱和成像的高均匀性场。由此启用的新对比机制 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磁场下的弛豫参数， 可以区分在这些场中具有不同相对弛豫速率的对比源。这将有助于 相对于背景量化成像剂浓度或区分表现出以下特征的个体药剂的状态： 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， 足够高的温度裕度以避免淬火。两个场之间的场切换时间将很快 足够（<1 s）以保持极化和弛豫测定，但对动物和人安全。我们的其他应用 开关场磁体可能包括介入MR和术中手术。在0.5 T磁化率伪影下 来自轻微磁性设备和植入物的射频加热和来自导电设备的射频加热要少得多。我们相信 随着磁共振波谱学和成像技术的进步，图像可以与1.5T相媲美。我们 相信我们提出的开关场MR磁体不仅可以保证新的对比机制， 也可以作为临床前动物甚至人类MRI的垫脚石， 常规MRI磁体。具体目标是开发一种无LHe的快速切换场MRI磁体 通过结合两个HTS磁体（2.5 T开关场磁体和0.5 T MRI磁体）的原型， 证明在快速场切换（高达3 T/s）期间的MRI场均匀性和稳定性。我们还将表演 具有最佳设计磁场的人体尺寸快速切换磁场MRI磁体的概念设计。独特的 我们的磁铁设计的特点是非常低的损耗和稳定的快速切换领域，不可能与一个 传统的低温超导体（LTS），以及两个独立运行的HTS的配置 磁体-高均匀性的稳定低场和中等场质量的快速循环高场-以实现 在性能和成本上具有快速切换的特点。我们的固体氮冷却低温系统不 依赖于氦，而氦已经成为一种稀缺且不可靠的商品。该项目的成功完成将 为更大（包括人类规模）和更高磁场的磁体铺平道路，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.