Microscopic MRI with Joule-Thomson Micro-Refrigerators

0071837 wright磁共振微成像（u-MRI）由于其非破坏性、非侵入性和丰富多样的对比度机制，已成为材料微观表征的宝贵工具，尽管许多生成对比度的技术存在低信噪比（SNR）的问题。然而，近年来的一项技术创新是使用高tc超导体（HTS）材料构建极高保真度的射频（RF）探测器线圈，以大大提高生物组织的u-MRI信噪比。虽然低温冷却射频线圈的回报可能是巨大的，正如最近对传统铜制线圈的演示，线圈通常冷却到约40 K，并且必须保持在接近被成像的（体温）组织的位置。因此，它们的实施对现有的低温技术提出了重大挑战，目前的解决方案引起了人们对液态低温危害的关注。然而，最近，一种新型的两级焦耳-汤姆逊微型制冷机已经开发出来，能够在35 K的温度下持续工作。这项工作提出了一种低温探针设计的新方法，适用于由传统和高温超导材料制成的线圈，其中包括通过这种微型焦耳-汤姆逊冰箱进行精确冷却。这种有待探索和开发的新方法代表了对u-MRI重要的现有技术的重大变化，也是该领域低温工程的创新，并可能对生物医学研究产生广泛影响。它还包含一个风险因素，因为它寻求应用新颖的焦耳-汤姆逊微制冷技术来推进u-MRI低温学的新兴子领域，但它有可能承认以前因信噪比限制而无法使用的成像和光谱技术。本工作所开发的微低温探针将作为u-MRI和核磁共振（NMR）光谱学的新工具应用于正常和病理组织以及具有医学意义的生物结构。应用可能包括骨小梁结构和脊髓损伤的体内成像，小鼠大脑的体外成像，以及生物相关细胞和液体的体外高场核磁共振波谱。据设想，这些工具将允许对组织微观结构和组成进行更准确的定量分析，对代谢性骨病、脊髓损伤和修复、发育中的大脑基因表达和癌症的理解、诊断和治疗产生影响。

0071837WrightMagnetic resonance micro-imaging (u-MRI) has become an invaluable tool for the microscopic characterization of materials due to its non-destructive, non-invasive nature and the rich variety of available contrast mechanisms, although many of the techniques for generating contrast suffer from low signal-to-noise ratio (SNR). A technological innovation of recent years, however, has been the use of high-Tc superconductor (HTS) materials to construct radio frequency (RF) detector coils of extremely high fidelity for greatly increased SNR in u-MRI of biological tissues. While the rewards of cryogenically cooling the RF coil can be great, as recently demonstrated for conventional coils made of copper, the coils are typically cooled to about 40 K and must be maintained in close proximity to the (body-temperature) tissue being imaged. Their implementation thus has posed significant challenges to existing cryogenic technology, with current solutions raising concern over the hazards of liquid cryogens. Very recently, however, a new type of two-stage Joule-Thomson micro-refrigerator has been developed, capable of sustained operation at 35 K. This work proposes a new approach to cryogenic probe design, applicable to coils made from both conventional and HTS materials, that involves precision cooling by means of such micro-miniature Joule-Thomson refrigerators. This new approach to be explored and developed represents a substantial change in the existing technology important to u-MRI as well as an innovation in cryogenic engineering specific to this field and is likely to have broad implications for biomedical research. It also contains an element of risk in that it seeks to apply novel Joule-Thomson micro-refrigeration technology to advance the emerging sub-field of u-MRI cryogenics, yet it has potential to admit imaging and spectroscopy techniques previously precluded by the limits of SNR.The micro-cryo-probes to be developed in this work will have application as new tools for u-MRI and nuclear magnetic resonance (NMR) spectroscopy of normal and pathological tissues and biological structures of medical significance. Applications may include in vivo imaging of trabecular bone structure and spinal cord injuries, ex vivo imaging of the mouse brain, and in vitro high-field NMR spectroscopy of biologically relevant cells and fluids. It is envisioned that such tools will permit more accurate quantitative analyses of tissue microstructure and composition, with impact on the understanding, diagnosis and treatment of metabolic bone diseases, spinal cord injury and repair, genetic expression in the developing brain, and cancer.