The central goal of this project is to introduce, develop, and establish novel RF volume exciters, to advance RF coil designs in human magnetic resonance imaging (MRI) at both 3 T - 4.7 T [high field (HF) MRI; current state-of-the-art clinical scanners) and 7 T [ultra-high field (UHF) MRI; predicted next-generation clinical scanners]. The main area of engineering research in advancing MRI scanners is in improving RF coils (exciters) and RF-excitation circularly polarized magnetic fields. Our approach and novel method for multi-channel excitation of RF magnetic field is predominantly based on subject-loaded multifilar helical-antenna RF volume coils as well as coil arrays for HF and UHF MRI. Our focus is developing, optimization, and realization of RF coils for 4.7 T operation, chosen for this research right midway between 3 T (current best, yet to be advanced and broadly adopted at clinics and hospitals) and 7 T (expected next big clinical overhaul in the near future, yet with lots of unknowns and challenges). This research is aimed to, in a longer term, advance both state-of-the-art clinical HF MRI scanners and next-generation UHF MRI systems. The major outcomes of the project can be summarized as follows.

Methodologies and technologies that were developed in this project are aimed to provide a new method of medical imaging with substantially increased RF power deposition in the imaged subject, power efficiency, RF field uniformity in the imaged area, field of view, imaging sensitivity, and resolution in diagnostics. The principal outcome of this research is to provide improved RF performance while potentially preserving the easiness of use of a volume coverage coil.

There is a lack of reported numerical and experimental results in literature for RF coils and exciters at 4.7 T, and our development, MR measurements in a 4.7-T human-size scanner, and analysis of multi-channel helix MR RF volume coils at this extremely interesting and rewarding intermediate field strength (midway between 3 T and 7 T) and Larmor frequency are unique and the first of its kind in many aspects.

Our studies of RF magnetic field profiling with a dielectric bore lining and other types of dielectric inclusions, such as dielectric lenses, for high-field and ultra-high-field MRI, may have impact on translating traveling wave MRI ideas to 3-T scanners and on better focusing the electromagnetic energy into the imaged phantom or subject at 7 T.

Our novel microstrip array RF coil for ultra-high-field MRI outperforms the stripline array coil, which is considered the best existing UHF MRI RF coil, in all of the simulation results. The novel microstrip model has lower S-parameter values, lower coupling, higher accepted power with a uniform field. The new coil shows lower transmission-line losses, more closely related modal velocities and lower dispersion, higher transmit efficiencies than stripline coil, as well as design flexibilities which can be simply exploited.

The recently optimized novel microstrip array RF coil at 4.7T, 200 MHz, showed a nearly 200% improvement over a standard stripline design of equal channels and similar geometric characteristics for maximum field efficiency, and a significant improvement in field uniformity. This new coil design offers many additional performances over the standard stripline design in terms of RF shimming and electrical interfaces. The new microstrip array design at 4.7T showed that what was previously thought to be effective only at ultra-high field, >7T, was applicable to the high-field regime, with potential for even lower field strengths such as 3T.

The MR images of the novel microstrip array and multi-channel helical antenna RF coil prototypes obtained in a 4.7 Tesla human MRI scanner are first such MR results for RF coils of these types at 4.7 T. The measured results showed ample field distribution across the phantoms and clear images, and were in excellent agreement, in post-imaging analysis, with computational electromagnetic simulations at 200 MHz, validating the field distributions and efficiency of each of the coils.

This grant has resulted so far in 21 journal and conference papers and presentations and three US patents.

This project has directly provided research training and development of five PhD graduate students, supported fully or partially by this grant as Research Assistants, as well as three REU undergraduate students supported as REU stipends. One graduate student is now a researcher in Keysight Technologies and another is now a researcher in HP. The project provided excellent education and research training for the students, whose gained expertise in computational and applied electromagnetics, antennas, and bio-electromagnetics would be an asset to any future employer in academia, government, or industry.  In their learning and research, the students were integrating numerous advanced research tools and interdisciplinary knowledge from electromagnetic theory, RF/antennas, microwaves, computational algorithms, MRI technology, and programming. The project has also furthered the education of 18 seniors on the ECE senior design projects on RF Design for Next-Generation MRI Scanners over several years.

Last Modified: 01/09/2025
Modified by: Branislav M Notaros