Collaborative Research: Electromagnetic Field Profile Design for Next-Generation Travelling-Wave MRI

合作研究：下一代行波 MRI 的电磁场轮廓设计

• 批准号: 1307614
• 负责人: Zoya Popovic
• 金额: $ 20万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1307614&HistoricalAwards=false
• 关键词: Collaborative; Research; Electromagnetic; Field; Profile

This collaborative proposal develops a new method of integrated design of exposure and excitation of electromagnetic (EM) fields in the UHF and low microwave frequency range for next-generation magnetic resonance imaging (MRI) at high magnetic fields (B3T). High magnetic fields improve the signal-to-noise ratio in MRI, and are accompanied by increased RF frequencies, which can lead to propagating modes inside the bore with a patient. For example, at 7T, the required RF frequency is in the 300MHz range, while a bore that fits a human is at least 60cm in diameter, making it above the cutoff frequency for at least one mode of the bore viewed as a waveguide, when loaded with the body. The travelling waves can potentially be advantageous in terms of a more comfortable environment for patients, larger field of view, imaging to-date MRI inaccessible areas, and enabling new spatial encoding schemes and a variety of mode sensitivity profiles. It is important, however, to be able to design the modes in the bore for better excitation field profile uniformity and control of power exposure to the body. Intellectual Merit: The principal goal of the proposed research is development of design methodologies for RF field profiles and associated cavity wall surface impedances and excitation probes, enabled by extremely fast and accurate full-wave higher order computational EM simulations of large body-loaded cavities. Several of the designs will be fabricated, characterized, and transitioned to clinical and research collaborators at Harvard University for imaging research. The specific issues to be addressed are: (a) Understanding the fundamental principles and limitations of radio-frequency electromagnetic field profile design for next-generation travelling-wave, high-field MRI; (b) Developing an engineering approach for modification of surface impedances in body-loaded bore cavities, enabled by extremely fast and reliable simulation techniques; (c) Solving the problem of proper field profile excitation (probe) design integrated with loaded cavity; (d) Evaluation and control of specific absorption rates inside the phantom, animal, or human; and (e) Implementing the designs for several clinical and research MRI machines operated by collaborators at Harvard University (these implementations are not supported by the proposed grant). The project will investigate periodic or quasi-periodic surface impedance structures in the form of printed resonant structures or three-dimensional dielectric-metal artificial surface impedances, and different types of excitations combining wire dipoles and loops, patch-antenna probes with coaxial feeds, and cavity backed slot exciters (multiple probes for different modes will be incorporated with switching circuits). Other (non-MRI) applications of the resulting research in loaded multi-mode cavities include areas from low-power wireless power delivery in closed spaces to high-power advanced smart microwave ovens. Broader impacts of the proposed work on basic science and engineering support the nation's science and technology advantage. The anticipated results will provide a new method of medical imaging with more comfort for patients, and an increased field of view, sensitivity, and functionality. Broader impacts on society are especially warranted by growing needs for such improved medical diagnostic tool. Because of the potential to change the way medical diagnostics using MRI is done in the longer term, the proposal may be considered transformative in its nature. Multi-disciplinary education at the undergraduate and graduate levels, spanning areas of high-frequency analog circuit design, EM simulations, bio-EM, and metrology, will make an impact on two top institutions in the state of Colorado, strengthening the existing core competency. The PIs at both institutions have been active in outreach, and related to this proposed work plan to add several new modules to the existing K-12 outreach, with hundreds of middle-school children on "Electric Field Trip" visits. A recruiting effort at all levels focusing on underrepresented groups will continue to enrich the educational environments. Collaborations related to medical applications with Harvard and Intermountain Neuroimaging Consortium, international collaboration with XLIM, University of Limoges, in France, and industry partnership (NXP) are evidenced by no-cost technical participation and insertion into clinical studies, student exchanges, and hardware donations.

这一合作方案为下一代高磁场磁共振成像(B3T)开发了一种新的集成设计方法，用于超高频和低微波频率范围内的电磁场曝光和激励。高磁场提高了磁共振成像的信噪比，并伴随着射频频率的增加，这可能导致患者钻孔内的传播模式。例如，在7T时，所需的射频频率在300 MHz范围内，而适合人体的弹孔直径至少为60厘米，当加载到人体时，使其高于至少一个被视为波导的弹孔模式的截止频率。行波可能在为患者提供更舒适的环境、更大的视野、成像最新的MRI无法到达的区域以及支持新的空间编码方案和各种模式敏感性配置文件方面具有潜在优势。然而，重要的是能够设计炮膛中的模式，以获得更好的激励场分布均匀性和对身体的功率暴露的控制。智力优势：拟议研究的主要目标是开发射频场分布以及相关腔壁表面阻抗和激励探头的设计方法，通过对大型体载腔体进行极快且准确的全波高阶计算电磁模拟来实现。其中几个设计将被制造、表征，并过渡到哈佛大学的临床和研究合作者进行成像研究。要解决的具体问题是：(A)了解下一代行波、高场磁共振的射频电磁场剖面设计的基本原理和局限性；(B)开发一种工程方法，通过极快速和可靠的模拟技术，修改身体负载的钻孔腔中的表面阻抗；(C)解决与加载的腔体相结合的适当的场剖面激励(探头)设计的问题；(D)评估和控制体模、动物或人体内的特定吸收率；以及(E)实施由哈佛大学合作者运营的几台临床和研究核磁共振机器的设计(这些实施不受拟议拨款的支持)。该项目将研究印刷谐振结构或三维介质-金属人工表面阻抗形式的周期性或准周期性表面阻抗结构，以及结合线偶极子和环路的不同类型的激励、具有同轴馈电的贴片天线探头和腔背缝隙激励器(不同模式的多个探头将与开关电路结合)。在加载的多模腔中所产生的研究的其他(非磁共振)应用包括从封闭空间中的低功率无线功率传输到高功率先进的智能微波炉。拟议工作对基础科学和工程的更广泛影响支持了国家的科学和技术优势。预期的结果将为患者提供一种更舒适的新的医学成像方法，并增加视野、灵敏度和功能性。对这种改进的医疗诊断工具的需求日益增长，尤其需要对社会产生更广泛的影响。由于从长远来看，这项提议可能会改变使用核磁共振进行医疗诊断的方式，因此这项提议可能会被认为具有变革性。本科生和研究生水平的多学科教育，横跨高频模拟电路设计、EM仿真、生物EM和计量学等领域，将对科罗拉多州的两所顶尖大学产生影响，加强现有的核心竞争力。这两个机构的主管一直积极开展外联活动，并与这项拟议的工作计划有关，在现有的K-12外联活动中增加了几个新的单元，数百名中学生参加了“电子实地考察”。各级以任职人数不足的群体为重点的招聘工作将继续丰富教育环境。与哈佛大学和山间神经成像联盟在医疗应用方面的合作，与法国利摩日大学XLIM的国际合作，以及与恩智浦的行业合作伙伴关系，都体现在免费的技术参与和临床研究、学生交流和硬件捐赠上。