A Preliminary Study for Reference RF Coil at 11.7 T MRI: Based on Electromagnetic Field Simulation of Hybrid-BC RF Coil According to Diameter and Length at 3.0, 7.0 and 11.7 T

Seo, Jeung-Hoon; Chung, Jun‐Young

doi:10.3390/s22041512

Cited by 6 publications

(9 citation statements)

References 88 publications

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“…By distributing series capacitors on both end-ring and leg conductor segments this issue is avoided. In addition, the hybrid topology has a more balanced field/voltage distribution across its structure leading to improved insensitivity to loading and avoiding large conservative electric fields that would increase the localized SAR [30], [31]. A 1.4 m long conductive shield with 55 cm diameter encompasses both designs in simulation to account for the outer conductor (RF shield) of the bore.…”

Section: Practical Metamaterials Liner a Metamaterials Liner And Bird...mentioning

confidence: 99%

“…By placing distributed series capacitors on both end-ring and leg conductor segments this mode can be excited despite the large dimensions of the coil. In addition, the hybrid topology has a more balanced field/voltage distribution across its structure leading to greater insensitivity to loading and minimizing large conservative electric fields that would increase the localized SAR [30], [31].…”

Section: Alternative Bc Sar Reduction Strategiesmentioning

confidence: 99%

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Metamaterial Liner for MRI Excitation—Part 2: Design and Performance at 4.7T

2022

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The theoretical foundations of a metamaterial (MM) liner for the MRI bore that facilitates the propagation of reduced-cutoff cylindrical waveguide modes are presented in the Part 1 companion paper to this work. Here, in Part 2, the practical design and modelling of the novel MM liner is applied to a body MRI radio-frequency (RF) transmitter for 4.7T. An equivalent network mesh model is developed to reduce the distributed structure of the MM to one that uses lumped discrete tuning elements. The close match between full-wave simulation and the network model is demonstrated by comparison of the longitudinal propagation dispersion curves and input impedance. The application of the methods developed for analysis of the MM liner behavior are demonstrated in the design of a practical MM liner as an effective MRI RF transmitter. The liner's simulated performance was evaluated using three key metrics of MR radio-frequency (RF) coil performance: transmit efficiency, the variation of the transmit field (a measure of homogeneity), and the 10g averaged local specific absorption rate (SAR). These metrics are compared to those of the commonly used birdcage (BC) coil. The main advantage of the MM liner is the 29.6% reduction in maximum SAR normalized to transmit field relative to the BC coil, with comparable transmit efficiency and homogeneity. Thus, the liner can potentially replace the BC coil as an RF transmitter and provide an enhanced safety margin, or allow the use of faster, more SAR-aggressive imaging sequences.

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Section: Practical Metamaterials Liner a Metamaterials Liner And Bird...mentioning

confidence: 99%

Section: Alternative Bc Sar Reduction Strategiesmentioning

confidence: 99%

Metamaterial Liner for MRI Excitation—Part 2: Design and Performance at 4.7T

2022

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“…Plasma ignition in a plasma source with the birdcage resonator at a frequency relevant to today's state-of-the-art MRI devices [13], [14] was not studied up to this moment. Our team have already brought preliminary work on this topic [15], [16]; however, only the electrical properties of the resonators have been studied yet.…”

Section: Introductionmentioning

confidence: 99%

Design and Fabrication of Birdcage Resonators for Low-pressure Plasma Excitation

Jurik¹,

Stary²,

Drexler³

2023

RADIOENGINEERING

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This paper presents a design, analysis and optimization of birdcage resonators employed in a novel radiofrequency plasma source. Three resonators were simulated and fabricated. The resonators differ in their design and in the different materials of used dielectric -polyimide and polytetrafluorethylene (PTFE). The resonance frequency of fabricated samples possesses a maximal error of 2.2% compared to the simulated values. The performance in plasma excitation is related to the electrical parameters, while the best performing resonator (PTFE-based) exhibits the maximum real impedance of 644.3 Ω at the resonance frequency and the 799.5 V/m electric field strength. This resonator shows the best power efficiency in a plasma ignition experiment. The resonator ignited the discharge at ca. 1 Pa of ambient air atmosphere with only 0.34 W of input radiofrequency power.

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“…A conventional MRI is a closed system with a bore diameter of 60 cm and a magnetic field of 1.5 T. Recently, open MRI FIGURE 1 (a) Electrical circuit of MRI system and (b) trimmer location in matching block [1] γ is equal to 42.58 MHz/T [3]. The 3 T magnetic field strength implies higher operating frequencies f Larmor (128 MHz versus 64 MHz for traditional closed MRI systems), which leads to better tissue penetration and thus improving the image quality [4].…”

Section: Introductionmentioning

confidence: 99%

“…At the end of the RF excitation, each atom sends back a RF wave with a frequency depending on its position. The information is then processed to build a 3D image [1].…”

Section: Introductionmentioning

confidence: 99%

FEM simulation‐based development of a new tunable non‐magnetic RF high voltage capacitor for the new generation of MRI

Jebri

Bord‐Majek

Bardet

et al. 2022

The Journal of Engineering

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Using Radio Frequency (RF) waves, magnetic resonance imaging (MRI) systems can make detailed images of human organs for accurate diagnostic processes and disease detection. The overhaul of certain electronic components has become necessary to keep up with the progress of MRI systems. Among the components responsible for image quality, the adjustable non-magnetic capacitors, also called trimmers, are of great importance. The purpose of this paper is to suggest a new design of a trimmer using non-magnetic materials, able to hold a high voltage ( >3 kV) and reach a resonance frequency above 100 MHz. Constructional analysis performed on existing commercial trimmers, combined with the electrical Finite Element Method, were carried out to propose a prototype matching the desired specifications. A dielectric shield surrounding the electrodes was sized to ensure voltage withstand. Moreover, the rotor and the worm-and-gear set were joined together to combat the vibrations generated by the MRI system. The present study includes the modelling step of the component by numerical simulation, the manufacturing, the electrical performance characterization, and the mechanical solution for tuning capacitance. The final prototype combines electrical performance corresponding to the required specifications in particular a high breakdown voltage (39.7 kV) and a resonance frequency (130 MHz).

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A Preliminary Study for Reference RF Coil at 11.7 T MRI: Based on Electromagnetic Field Simulation of Hybrid-BC RF Coil According to Diameter and Length at 3.0, 7.0 and 11.7 T

Cited by 6 publications

References 88 publications

Metamaterial Liner for MRI Excitation—Part 2: Design and Performance at 4.7T

Metamaterial Liner for MRI Excitation—Part 2: Design and Performance at 4.7T

Design and Fabrication of Birdcage Resonators for Low-pressure Plasma Excitation

FEM simulation‐based development of a new tunable non‐magnetic RF high voltage capacitor for the new generation of MRI

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