A Coaxial RF Applicator for Ultra-High Field Human MRI

A Coaxial RF Applicator for Ultra-High Field Human MRI

Objective: To develop a novel radio-frequency (RF) concept for ultra-high field (UHF) human magnetic resonance imaging (MRI) based on a coaxial resonant cavity. Methods: A two-channel slotted coaxial cavity RF applicator was designed for human head MRI at 9.4T. Physical dimensions made the proposed...

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Bibliographic Details
Published in:IEEE transactions on biomedical engineering Vol. 66; no. 10; pp. 2848 - 2854
Main Authors: Solomakha, Georgiy, Andreychenko, Anna, Moortele, Pierre-Francois van de, Kroeze, H., Raaijmakers, Alexander J., Euwe, F. E., Lagendijk, J. J. W., Luijten, P. R., Berg, C. A. T. van den
Format: Journal Article
Language:English
Published: United States IEEE 01-10-2019
The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subjects:
9.4T
Applicators
Arrays
Cavity resonators
Circular polarization
Coaxial radio-frequency applicator
Coils
Computer simulation
Design
Design optimization
Homogeneity
Impedance matching
Input impedance
Magnetic fields
Magnetic heads
Magnetic resonance imaging
Mapping
NMR
Nuclear magnetic resonance
Numerical models
Radio frequency
resonant cavity
Robustness (mathematics)
Safety engineering
Tuning
ultra high field
Ultrahigh frequencies
waveguide
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Summary:Objective: To develop a novel radio-frequency (RF) concept for ultra-high field (UHF) human magnetic resonance imaging (MRI) based on a coaxial resonant cavity. Methods: A two-channel slotted coaxial cavity RF applicator was designed for human head MRI at 9.4T. Physical dimensions made the proposed conducting structure resonant at the required frequency without tuning lumped elements. Numerical electromagnetic modeling was used to optimize the design. RF safety was assessed with two representative human body models. MR experiments on a 9.4T scanner included gradient echo images and mapping of a circularly polarized RF magnetic field in the human head phantom. Results: The simulations and the phantom MR experiments agreed both qualitatively and quantitatively. The design was relatively simple, robust and required only a few additional reactive elements for the applicator's input impedance matching. The transmit efficiency and homogeneity of the excitation field were only 20% and 4% lower compared to a conventional 8-channel head array. Conclusion: The coaxial RF applicator was feasible for human MRI at UHF and required no lumped elements for its tuning. Imaging performance of the RF applicator was only moderately lower compared to the conventional transmit array, but would be sufficient to provide an anatomical reference for the heteronuclei MRI. Significance: An alternative approach with the minimal involvement of lumped elements becomes feasible to design volume-type RF coils for UHF human MRI.
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ISSN:0018-9294
1558-2531
DOI:10.1109/TBME.2019.2897029