RF Aspects of High-Field Magnetic Resonance Imaging (HF-MRI): Recent Advances

Caverly, Robert H.

doi:10.1109/jerm.2018.2879396

Cited by 6 publications

(13 citation statements)

References 49 publications

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“…In particular, in clinical MRI systems under 7.0 T, quantitative performance evaluations are usually performed using a low-pass-type BC (LP-BC) RF coil. In clinical settings, to obtain high-field (HF) and ultrahigh-field (UHF) MRI signals and replace existing coil-based structures for low-field (LF) MRI, the demand for the development of new structures and electronic devices is increasing [4].…”

Section: Introductionmentioning

confidence: 99%

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

Chung

2022

Sensors

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Magnetic resonance imaging (MRI) systems must undergo quantitative evaluation through daily and periodic performance assessments. In general, the reference or standard radiofrequency (RF) coils for these performance assessments of 1.5 to 7.0 T MRI systems have been low-pass-type birdcage (LP-BC) RF coils. However, LP-BC RF coils are inappropriate for use as reference RF coils because of their relatively lower magnetic field (B1-field) sensitivity than other types of BC RF coils, especially in ultrahigh-field (UHF) MRI systems above 3.0 T. Herein, we propose a hybrid-type BC (Hybrid-BC) RF coil as a reference RF coil with improved B1-field sensitivity in UHF MRI system and applied it to an 11.7 T MRI system. An electromagnetic field (EM-field) analysis on the Hybrid-BC RF coil was performed to provide the proper dimensions for its use as a reference RF coil. Commercial finite difference time-domain program was used in EM-field simulation, and home-made analysis programs were used in analysis. The optimal specifications of the proposed Hybrid-BC RF coils for them to qualify as reference RF coils are proposed based on their B1+-field sensitivity under unnormalized conditions, as well as by considering their B1+-field uniformity and RF safety under normalized conditions.

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Section: Introductionmentioning

confidence: 99%

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

Chung

2022

Sensors

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“…M AGNETIC resonance imaging (MRI) is a goldstandard technique for the assessment of several human diseases, and it is capable to offer a wide range of anatomical and functional information [1], [2]. MRI aims to provide clinically relevant images with high-contrast using the quantum principle of nuclear magnetic resonance [3].…”

Section: Introductionmentioning

confidence: 99%

“…They also allow acquiring high-resolution images in a short time [5]. One of the fundamental components of MRIs are the radiofre-quency (RF) coils, which are responsible for transmitting and receiving signals from different areas of the human body and play a major role in determining the images' SNR [2]. RF coils can be mainly categorized into volume and surface coils [6].…”

Section: Introductionmentioning

confidence: 99%

“…Hexagonal coils have been proposed [8]- [10]. However, these shapes exhibited lower performance with stronger applied static magnetic fields, as the coil current path is electrically large, due to the limited wavelength (∼ 1 m @ 300 MHz, in air), increasing the coil radiation losses [2], [11]. Therefore, the octagonal configuration has been proposed [12], allowing the current to flow more easily in UHF, avoiding high current densities at the corners of the coil, [12], [13], minimizing the lateral skin effect [14], achieving larger magnetic sensitivity [15], and providing improved SNR [13].…”

Section: Introductionmentioning

confidence: 99%

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Analysis of a Flexible Dual-Channel Octagonal Coil System for UHF MRI

et al. 2022

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Nowadays, MRI is focused on using ultra-high static magnetic fields (> 7 T) to increase the signal-to-noise ratio. The use of high fields, on the other hand, requires novel technical solutions as well as more stringent design criteria for specific absorption rate levels, reducing radiative effect and coil resistance. In this paper, two flexible RF coils for 7 T human magnetic resonance, and 298 MHz ultrahigh frequency operations were analyzed and characterized. Imaging of lower human limbs is regarded as a case study. The lumped element theory and subsequent numerical simulations were used to finetune the single-coil element and the dual-coil array design, respectively. Here, we demonstrate how the shape, size, configuration, and presence of the sample influence the coil performance. The penetration depth of the B 1 -field and the specific absorption rate values have been determined numerically using two numerical surface phantoms: saline and a multilayer human tissue. A preliminary study in the presence of a saline solution phantom has been carried out to develop and validate the dual-coil system. The frequency response of the dual-coil array was measured to assess its robustness when coupled to twelve human volunteers. We found that our design is robust to variations in the anatomical properties of the human thighs, and hence to coil bending. The presented approach can be useful for the implementation of flexible devices with high sensitivity levels and low specific absorption rate.

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“…Though, this method is susceptible to human errors, and also lacks essential accuracy. To reduce errors, a number of standardized solutions have been used, such as magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound scan [8][9][10][11][12][13]. Several innovative methods have also been reported for microwave imaging purposes, as well as for biomedical detection and scanning [14,15].…”

Section: Introductionmentioning

confidence: 99%

Hybrid Development of a Compact Antenna Based on a Novel Skin-Matched Ceramic Composite for Body Fat Measurement

et al. 2020

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This work presents the thorough hybrid (numerical and experimental) development of a miniaturized microwave antenna, to be better matched to the permittivity of the human skin. This would allow the abdominal fat to be measured more accurately, based on the employed reflection methods with minimal mismatches. This objective was achieved by designing the pyramidal horn antenna that was modeled based on the proposed and manufactured ceramic composite material. Moreover, by using the developed composite of barium titanate and titanium oxide, the ratio of the two could be precisely adjusted, so that the permittivity was a reasonable match to that of the skin. This step was validated by the open-ended probe method. This framework can be instrumental in a range of microwave biomedical applications, which aim to realize the body-centric systems.

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RF Aspects of High-Field Magnetic Resonance Imaging (HF-MRI): Recent Advances

Cited by 6 publications

References 49 publications

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

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

Analysis of a Flexible Dual-Channel Octagonal Coil System for UHF MRI

Hybrid Development of a Compact Antenna Based on a Novel Skin-Matched Ceramic Composite for Body Fat Measurement

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