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Traveling-wave RF shimming and parallel MRI
David O Brunner1, Jan Paška, Juerg Froehlich
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
Magnetic Resonance in Medicine
|June 23, 2011
Summary
Researchers enabled multi-channel magnetic resonance imaging by using the magnet bore as a waveguide. This approach supports radiofrequency shimming and parallel imaging, enhancing magnetic resonance (MR) capabilities.
Area of Science:
- Magnetic Resonance Imaging
- Electromagnetism
- Waveguide Technology
Background:
- Traveling electromagnetic waves in magnet bores enable remote magnetic resonance (MR) excitation and detection.
- Current methods are limited to the lowest waveguide modes, restricting multi-channel operations like radiofrequency (RF) shimming and parallel imaging.
Purpose of the Study:
- To overcome limitations of single-mode waveguide operation in MR magnet bores.
- To enable multi-channel RF shimming and parallel imaging using diverse waveguide modes.
Main Methods:
- Increased the number of propagating modes in the magnet bore using dielectric inserts.
- Implemented multiple waveguide ports with stub and loop couplers for signal diversity.
- Tested a traveling-wave array at 298 MHz in a 7T whole-body magnet.
Main Results:
- Demonstrated successful radiofrequency shimming and parallel imaging with common acceleration factors.
- Determined that minimal dielectric loading (water-filled inserts occupying ~5% of bore cross-section) is sufficient.
- Showcased the effectiveness of a multi-mode traveling-wave array for advanced MR applications.
Conclusions:
- Multi-mode waveguide operation within a magnet bore significantly expands MR capabilities.
- This technique facilitates advanced MR techniques like RF shimming and parallel imaging.
- Efficient parallel imaging is achievable with modest dielectric loading in the waveguide.
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