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Excitation and RF Field Control of a Human-Size 10.5-T MRI System
Patrick Bluem1, Pierre-Francois Van de Moortele2, Gregor Adriany2
1Department of Electrical, Computer and Energy Engineering, University of Colorado, Boulder, CO 80309-0425 USA.
IEEE Transactions on Microwave Theory and Techniques
|November 22, 2019
Summary
Researchers improved magnetic field homogeneity in MRI scans using novel probe designs and boundary modifications. These advancements enhance imaging quality across various phantoms and human head models.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Electromagnetics
- Biomedical Engineering
Background:
- Achieving uniform transmit B1 fields is critical for high-resolution MRI, especially at ultra-high field strengths (UHF-MRI).
- Existing methods often struggle with homogeneity in diverse and anatomically complex dielectric phantoms.
- The 10.5 T MRI system presents unique challenges for B1 field uniformity.
Purpose of the Study:
- To investigate and demonstrate methods for enhancing transmit B1 field homogeneity in dielectric phantoms at 10.5 T.
- To evaluate the effectiveness of proposed techniques using both simulations and experimental measurements.
- To assess the impact of improved homogeneity on specific absorption rate (SAR) in human head models.
Main Methods:
- Utilized a quadrature-fed circular patch-probe and a 12-element capacitively-loaded microstrip array for B1 field excitation.
- Employed full-wave finite-difference time-domain (FDTD) simulations (Sim4Life) to analyze B1 field distribution.
- Modified electromagnetic boundary conditions with a passive quadrifilar helix for enhanced field uniformity.
Main Results:
- Demonstrated improved B1 field homogeneity in cylindrical water, pineapple, and NIST standard phantoms.
- Simulation results correlated well with gradient recalled echo (GRE) imaging and efficiency measurements.
- Application to a human head model (Duke) showed enhanced homogeneity and reduced specific absorption rate (SAR).
Conclusions:
- The proposed methods effectively improve B1 field homogeneity in various dielectric phantoms at 10.5 T.
- The integration of passive quadrifilar helix structures offers a viable strategy for further field uniformity enhancement.
- These advancements hold promise for improving image quality and safety in UHF-MRI applications, including human head imaging.
