Novel RF Volume Coils for High and Ultra-High Field Magnetic Resonance Imaging Scanners

磁共振成像（MRI）是一种成熟的医学诊断方法和工具，广泛用于获得身体或其部分和器官内部结构的高分辨率图像，其中被成像的组织的原子核吸收并重新发射施加的射频（RF）辐射。这是由所谓的射频线圈产生的射频激发磁场实现的，其频率与扫描仪磁铁的强度成正比，单位为特斯拉(T)。虽然最先进的临床MRI扫描仪是3-T系统，但运行在1.5 T的MRI机器仍然在医院中占据很大的优势。磁共振成像系统具有更强的磁铁和更高的射频频率，可以提供更高的图像分辨率，更快的检查，并为患者提供更多的舒适度，以及其他改进。然而，他们需要新的工程和设计方法，使他们的操作，安全和高效。推进核磁共振成像扫描仪的主要工程研究领域是改进射频线圈和磁场。这正是本研究项目的重点领域，旨在引入、开发、测试、评估和建立新型射频激发器，并推进射频线圈设计，用于最先进和下一代临床MRI扫描仪的3t、4.7 T、7t等磁体强度。本研究提出了一种新的科学方法和工程技术，以解决射频与核磁共振之间的接口和工程与科学之间的结合处的一个非常普遍和具有挑战性的问题，并具有直接的应用，因此它对科学和技术具有实质性的更广泛的影响。对基于人体、器官和组织的高分辨率成像的医疗诊断工具的巨大且不断增长的需求，尤其保证了对社会产生更广泛的影响。该项目的教育和推广计划包括加强课程材料和教学、研究生的咨询和培训、本科生的研究、代表性不足的群体、K-12的推广和国际合作。高场（HF） MRI扫描仪指的是3t至7t的主静态磁场（由磁铁产生），而超高场（UHF）是7t及以上。提出的射频磁场多通道激励的新方法和新方法是基于高频和超高频MRI的主体负载多丝状螺旋天线射频体积线圈，以推进3t（目前最好的，但仍在先进和广泛应用于诊所和医院）和7t（预计在不久的将来进行下一次重大临床改革，但有许多未知和挑战）的射频线圈设计。这种方法的新颖之处在于利用螺旋线圈的内部体积来激发目标样品。在7 T的幻影中获得的4通道和8通道螺旋线圈的初步MRI数据证明了所提出方法的可行性，实验结果与数值模拟之间具有一致性。在3t下的初步模拟表明，螺旋天线激振器提供了更好的射频场均匀性和更大的视场，与其他报道的结果相比，具有相当的发射效率。该项目将分别对3T和7t的多通道螺旋射频线圈进行表征、评估和改进。在此基础上，本研究将开发、优化并实现4.7 T运行线圈，选择在3 T和7 T之间，并通过模拟实验和仿真对射频效率、比吸收率分布和空间射频场编码进行量化。主要目标是提供改进的射频性能，同时潜在地保持体积覆盖线圈的易用性，确定拟议的新线圈结构提供的潜在收益，并进一步推进它们更接近临床前医学研究和实现全球范围内的临床实践。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Magnetic resonance imaging (MRI) is an established medical diagnostic method and tool widely utilized to obtain high-resolution images of the internal structure of the body or its parts and organs, where atom nuclei of the tissue that is imaged absorb and reemit applied radio-frequency (RF) radiation. This is enabled by RF-excitation magnetic fields generated by so-called RF coils, whose frequency is proportional to the strength of the scanner's magnet, in units of tesla (T). Whereas state-of-the-art clinical MRI scanners are 3-T systems, MRI machines operating at 1.5 T still prevail in hospitals by a very large margin. MRI systems with stronger magnets and higher RF frequencies can provide higher resolution of images, faster exams, and more comfort for patients, among other improvements. However, they require new engineering and design approaches to make them operational, safe, and efficient. The main area of engineering research in advancing MRI scanners is in improving RF coils and fields. This exactly is the area of focus of this research project, aimed at introducing, developing, testing, evaluating, and establishing novel RF exciters and advancing RF coil designs for magnet strengths of 3 T, 4.7 T, 7 T, etc., for both state-of-the-art and next-generation clinical MRI scanners. The proposed research provides a new scientific methodology and engineering technology to solve a very general and challenging problem at the interface between RF and MRI and junction between engineering and science and with immediate applications, and hence it has substantial broader impacts on science and technology. Broader impacts on society are especially warranted by great and growing needs for medical diagnostic tools based on high-resolution imaging of human bodies, organs, and tissues. Education and outreach plan of this project includes enhancing course materials and delivery, advising and training of graduate students, undergraduate research, underrepresented groups, K-12 outreach, and international collaboration.High-field (HF) MRI scanners are referring to the main static magnetic field (generated by magnet) from 3 T to 7 T, while ultra-high field (UHF) is 7 T and above. The proposed approach and novel method for multi-channel excitation of RF magnetic fields is based on subject-loaded multifilar helical-antenna RF volume coils for HF and UHF MRI, to advance RF coil designs at both 3 T (current best, yet to be advanced and broadly adopted at clinics and hospitals) and 7 T (expected next major clinical overhaul in the near future, yet with lots of unknowns and challenges). The novelty of this approach consists of using the inner volume of the helix coil to excite the target sample. Preliminary MRI data obtained in phantoms at 7 T with 4- and 8-channel helix coils demonstrated the feasibility of the proposed approach, with consistency between experimental results and numerical simulations. Preliminary simulations at 3 T show that the helical-antenna exciter provides better RF-field uniformity and larger field of view than other reported results, with comparable transmit efficiencies. The project will pursue characterization, evaluation, and advancement of multi-channel helix RF coils at 3T and 7 T, respectively. Based on the obtained results, it will develop, optimize, and realize coils for 4.7 T operation, chosen for this proposed research midway between 3 T and 7 T, with RF efficiency, specific absorption rate distribution, and spatial RF-field encoding quantified in phantom experiments and in simulations. Principal goals are to provide improved RF performance while potentially preserving the easiness of use for a volume coverage coil, to determine the potential gains offered by the proposed new coil structures, and to further advance them closer to preclinical medical research and realization for clinical practice on a more global scale.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.