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

Colorado State University, Fort Collins CO

Investigators

Abstract

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.