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: 1307863
• 负责人: Branislav Notaros
• 金额: $ 20万
• 依托单位: Colorado State University
• 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 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1307863&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.

该合作提案开发了一种在 UHF 和低微波频率范围内集成设计电磁 (EM) 场暴露和激励的新方法，用于高磁场 (B3T) 下的下一代磁共振成像 (MRI)。高磁场提高了 MRI 的信噪比，并伴随着射频频率的增加，这可能导致患者孔内的传播模式。例如，在 7T 时，所需的 RF 频率在 300MHz 范围内，而适合人体的孔直径至少为 60cm，使其高于被视为波导的孔的至少一种模式的截止频率，当装载着身体。行波在为患者提供更舒适的环境、更大的视野、对最新 MRI 无法到达的区域进行成像以及实现新的空间编码方案和各种模式灵敏度配置文件方面具有潜在的优势。然而，重要的是能够设计孔中的模式，以实现更好的激励场分布均匀性和对身体功率暴露的控制。 智力优点：所提议研究的主要目标是开发射频场轮廓和相关腔壁表面阻抗和激励探针的设计方法，通过对大型人体负载腔进行极快速和精确的全波高阶计算电磁模拟来实现。其中一些设计将被制造、表征并转移给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 MRI 射频电磁场分布设计的基本原理和局限性； (b) 开发一种工程方法，通过极其快速和可靠的模拟技术来修改人体负载孔腔中的表面阻抗； (c) 解决与负载腔集成的适当场分布激励（探头）设计问题； (d) 模型、动物或人体内部特定吸收率的评估和控制； (e) 实施哈佛大学合作者操作的几台临床和研究 MRI 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电金属人造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、具有同轴馈电的贴片天线探头和不同类型的激励。腔背槽激励器（用于不同模式的多个探头将与开关电路合并）。由此产生的研究成果在负载多模腔中的其他（非 MRI）应用包括从封闭空间中的低功率无线供电到高功率先进智能微波炉等领域。拟议的基础科学和工程工作的更广泛影响支持国家的科学和技术优势。预期结果将提供一种新的医学成像方法，使患者更加舒适，并增加视野、灵敏度和功能。对这种改进的医疗诊断工具的需求不断增长，尤其需要对社会产生更广泛的影响。由于从长远来看有可能改变使用 MRI 进行医疗诊断的方式，因此该提案在本质上可能被认为是变革性的。本科生和研究生的多学科教育，涵盖高频模拟电路设计、电磁仿真、生物电磁和计量学等领域，将对科罗拉多州的两所顶尖院校产生影响，加强现有的核心能力。两家机构的 PI 一直积极开展外展活动，并与拟议的工作计划相关，即在现有 K-12 外展活动中添加几个新模块，让数百名中学生进行电动实地考察。各级针对代表性不足群体的招聘工作将继续丰富教育环境。与哈佛大学和山间神经影像联盟在医学应用方面的合作、与法国利摩日大学 XLIM 的国际合作以及行业合作伙伴关系 (NXP) 均通过免费技术参与和插入临床研究、学生交流和硬件捐赠来证明。