Traveling Wave Approaches for Improved Sensitivity and Spatial Coverage in Continuous-Wave (CW) Electron Paramagnetic Resonance Imaging

电子顺磁共振成像（EPRI）是一种低成本、高特异性的成像技术，具有重要的应用价值。在医学成像中，EPRI可用于获得组织氧合图像，以识别组织缺氧区域。缺乏氧气的癌症区域通常更具侵袭性，更难治疗，因此识别缺氧的医学成像工具将非常有用。相对于其他医学成像技术，EPRI的主要优势是其仪器的成本明显较低。例如，与磁共振成像（MRI）相比，EPRI可以在不使用超导磁铁的情况下进行。与MRI系统相比，这大大降低了构建、选址和操作EPRI系统的成本。然而，与MRI不同的是，使用EPRI进行全身人体成像的技术尚未开发出来。EPRI进一步发展的主要挑战之一是难以在高灵敏度成像所需的频率范围内进行信号激励。该项目通过开发新型仪器解决了这一缺点，最终使EPRI系统能够用于全身人体成像。该项目的成功完成将为低成本人体成像技术的发展提供潜力。由于这项技术提供了类似于核磁共振成像的成像能力，但成本只是其一小部分，因此预计将大大降低基于成像技术的医疗诊断技术的成本。这可能有助于降低向美国和世界各地公众提供的整体医疗保健服务的成本。此外，该项目具有重要的教育影响，包括增加代表性不足的学生参与研究和研究生工程教育，本科生积极参与研究，指导K-12科学教师和课程开发，以及向公众广泛传播研究成果。该项目的总体目标是开发连续波（CW）电子顺磁共振成像（EPRI）的新技术，提高其灵敏度，并朝着能够进行全身人体成像的仪器发展。具体来说，我们建议发展一种行波（TW）方法用于连续波电子顺磁共振成像。在TW方法中，射频信号激励是使用从波导内的远程天线或探头通过组织传播的行波来执行的。与传统的反应性近场方法相比，使用TW方法可以实现更大体积上的均匀磁场。因此，连续波的发展，TW-EPRI有望实现必要的体积覆盖和足够高的磁场强度，需要进行全身人体成像。为了实现这一目标，我们将追求四个目标，开发和研究新颖，低成本的CW， TW-EPRI仪器。其中包括：1)在平行板波导环境中开发连续波行波EPRI系统，以证明行波EPRI系统的可行性；2)开发相控阵发射技术，以改善高频（300 MHz）连续波，TW-EPRI系统的磁场均匀性；3)整合成像系统，开发改进的重建算法；4)开发加速图像采集速度和提高CW、TW-EPRI系统灵敏度的技术。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。

Electron paramagnetic resonance imaging (EPRI) is a low-cost and highly specific imaging technique with significant applications. In medical imaging, EPRI can be used to obtain tissue oxygenation images to identify oxygen-starved areas of tissue. Oxygen-starved areas of cancer are usually more aggressive and harder to treat, so a medical imaging tool to identify hypoxia would be highly useful. A primary advantage of EPRI relative to other medical imaging techniques is the significantly lower cost of its instrumentation. For example, in comparison to magnetic resonance imaging (MRI), EPRI can be performed without using a superconducting magnet. This drastically reduces the cost of constructing, siting, and operating EPRI systems compared to MRI systems. Unlike MRI, however, the technology for using EPRI to perform whole-body human imaging has not yet been developed. One of the primary challenges in further development of EPRI is the difficulty in performing signal excitation at the frequency ranges that are desirable for high-sensitivity imaging. This project addresses this shortcoming by developing novel instrumentations that will ultimately enable EPRI systems to be used for whole-body human imaging. The successful completion of this project has the potential for the development of a low-cost, human imaging technology. Since this technology offers imaging capabilities similar to MRI but at a small fraction of its cost it is expected to significantly reduce the cost of medical diagnostic techniques based on imaging technologies. This will likely contribute towards reducing the cost of overall healthcare services provided to the public in the U.S. and around the world. Additionally, this project has important educational impacts, which include increased participation of under-represented students in research and graduate engineering education, active involvement of undergraduate students in research, mentoring K-12 science teachers and curriculum development, and broad dissemination of research results to the public.The overall objective of this project is to develop new techniques for continuous-wave (CW) electron paramagnetic resonance imaging (EPRI) that enhance its sensitivity and move towards the development of instrumentation capable of whole-body human imaging. Specifically, we propose to develop a traveling-wave (TW) approach for continuous-wave electron-paramagnetic resonance imaging. In the TW approach, RF signal excitation is performed using traveling waves that propagate from a remote antenna or probe inside a waveguide through tissue. In comparison to the conventional reactive near field approach, uniform magnetic fields across a much larger volume can be realized using the TW approach. Therefore, the development of the continuous-wave, TW-EPRI is expected to enable both the necessary volumetric coverage and sufficiently high magnetic field strength needed to perform whole-body human imaging. To accomplish this, we will pursue four aims to develop and study novel, low-cost CW, TW-EPRI instrumentation. These include: 1) develop a CW, traveling-wave EPRI system in a parallel plate waveguide environment to demonstrate feasibility for a traveling wave EPRI system; 2) Develop phased-array transmit techniques for improved magnetic field uniformity in high-frequency (300 MHz) continuous-wave, TW-EPRI systems; 3) Integrate the imaging system and develop improved reconstruction algorithms; and 4) Develop techniques for accelerating image acquisition speed and improving the sensitivity of CW, TW-EPRI systems.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.