scholarly journals A 16-Channel Dipole Antenna Array for Human Head Magnetic Resonance Imaging at 10.5 Tesla

Sensors ◽  
2021 ◽  
Vol 21 (21) ◽  
pp. 7250
Author(s):  
Myung Kyun Woo ◽  
Lance DelaBarre ◽  
Matt Waks ◽  
Jerahmie Radder ◽  
Uk-Su Choi ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Antenna Array ◽  
Antenna Arrays ◽  
Human Head ◽  
Biological Tissues ◽  
Dipole Antenna ◽  
Human Model ◽  
Resonance Imaging ◽  
Array Configuration

For ultra-high field and frequency (UHF) magnetic resonance imaging (MRI), the associated short wavelengths in biological tissues leads to penetration and homogeneity issues at 10.5 tesla (T) and require antenna transmit arrays for efficiently generated 447 MHz B1+ fields (defined as the transmit radiofrequency (RF) magnetic field generated by RF coils). Previously, we evaluated a 16-channel combined loop + dipole antenna (LD) 10.5 T head array. While the LD array configuration did not achieve the desired B1+ efficiency, it showed an improvement of the specific absorption rate (SAR) efficiency compared to the separate 8-channel loop and separate 8-channel dipole antenna arrays at 10.5 T. Here we compare a 16-channel dipole antenna array with a 16-channel LD array of the same dimensions to evaluate B1+ efficiency, 10 g SAR, and SAR efficiency. The 16-channel dipole antenna array achieved a 24% increase in B1+ efficiency in the electromagnetic simulation and MR experiment compared to the LD array, as measured in the central region of a phantom. Based on the simulation results with a human model, we estimate that a 16-channel dipole antenna array for human brain imaging can increase B1+ efficiency by 15% with similar SAR efficiency compared to a 16-channel LD head array.

scholarly journals Dipole-Fed Rectangular Dielectric Resonator Antennas for Magnetic Resonance Imaging at 7 T: The Impact of Quasi-Transverse Electric Modes on Transmit Field Distribution

2021 ◽  
Vol 9 ◽  
Author(s):  
Daniel Wenz ◽  
Rolf Gruetter
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Field Distribution ◽  
Human Head ◽  
Dipole Antenna ◽  
Resonance Imaging ◽  
Dipole Antennas ◽  
Rectangular Block ◽  
The Impact

Shortened dipole antennas based on rectangular dielectric blocks play an important role in ultrahigh field magnetic resonance imaging (UHF-MRI) radio frequency (RF) coil design. However, the generally assumed direct contact with the subject is difficult to maintain in typical in vivo settings. We have previously observed that certain dielectrically shortened dipole antennas can produce a substantially altered transmit field distribution with a very low transmit efficiency when the block and the sample are physically separated. Therefore, the aim of this study was to determine a) why certain designs of dielectrically shortened dipole antennas can produce an inefficient transmit field when the block and the sample are physically separated and b) how this depends on key parameters such as rectangular block geometry, dielectric constant, loading geometry, and RF feeding. In this work, two main types of quasi-transverse dielectric modes were found in different rectangular block geometries and interpreted as TE11δz (MR efficient) and TE1δδy (MR inefficient), and their impact on in vivo MRI experiments involving the human head, calf, and wrist was explored. This study shows, for the first time, why certain antennas preserve their transmit field efficiency despite physical separation from the sample. We conclude that the proposed approach has the potential to provide new insights into dipole antenna design for UHF-MRI.

scholarly journals Evaluation of 8-Channel Radiative Antenna Arrays for Human Head Imaging at 10.5 Tesla

Sensors ◽  
2021 ◽  
Vol 21 (18) ◽  
pp. 6000
Author(s):  
Myung Kyun Woo ◽  
Lance DelaBarre ◽  
Matt Thomas Waks ◽  
Young Woo Park ◽  
Russell Luke Lagore ◽  
...  
Keyword(s):  
Antenna Array ◽  
Antenna Arrays ◽  
Specific Absorption Rate ◽  
Human Head ◽  
Dipole Antenna ◽  
Monopole Antenna ◽  
Human Model ◽  
Head Model ◽  
Coaxial Feed ◽  
Substantial Drop

For human head magnetic resonance imaging at 10.5 tesla (T), we built an 8-channel transceiver dipole antenna array and evaluated the influence of coaxial feed cables. The influence of coaxial feed cables was evaluated in simulation and compared against a physically constructed array in terms of transmit magnetic field (B1+) and specific absorption rate (SAR) efficiency. A substantial drop (23.1% in simulation and 20.7% in experiment) in B1+ efficiency was observed with a tight coaxial feed cable setup. For the investigation of the feed location, the center-fed dipole antenna array was compared to two 8-channel end-fed arrays: monopole and sleeve antenna arrays. The simulation results with a phantom indicate that these arrays achieved ~24% higher SAR efficiency compared to the dipole antenna array. For a human head model, we observed 30.8% lower SAR efficiency with the 8-channel monopole antenna array compared to the phantom. Importantly, our simulation with the human model indicates that the sleeve antenna arrays can achieve 23.8% and 21% higher SAR efficiency compared to the dipole and monopole antenna arrays, respectively. Finally, we obtained high-resolution human cadaver images at 10.5 T with the 8-channel sleeve antenna array.

scholarly journals Monopole antenna array design for 3 T and 7 T magnetic resonance imaging

PLoS ONE ◽  
2019 ◽  
Vol 14 (4) ◽  
pp. e0214637
Author(s):  
A. S. M. Zahid Kausar ◽  
David C. Reutens ◽  
Ewald Weber ◽  
Viktor Vegh
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Antenna Array ◽  
Monopole Antenna ◽  
Resonance Imaging ◽  
Array Design

Numerical Evaluation of Heating of the Human Head Due to Magnetic Resonance Imaging

2004 ◽  
Vol 51 (8) ◽  
pp. 1301-1309 ◽  
Author(s):  
U.D. Nguyen ◽  
J.S. Brown ◽  
I.A. Chang ◽  
J. Krycia ◽  
M.S. Mirotznik
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Numerical Evaluation ◽  
Human Head ◽  
Resonance Imaging

scholarly journals A numerical study of pre-polarisation switching in ultra-low field magnetic resonance imaging using dynamic permanent magnet arrays

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Ruben Pellicer-Guridi ◽  
Michael W. Vogel ◽  
Viktor Vegh ◽  
Jiasheng Su ◽  
Matthew S. Rosen ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Permanent Magnet ◽  
Structural Integrity ◽  
Numerical Study ◽  
Human Head ◽  
Von Mises Stress ◽  
Resonance Imaging ◽  
Polarisation Field ◽  
Low Field

Abstract Dynamically adjustable permanent magnet arrays have been proposed to generate switchable magnetic fields for pre-polarisation in Ultra-Low Field magnetic resonance imaging. However, the optimal switching dynamics of the pre-polarisation magnetic field as well as the energy requirements, mechanical forces and stresses during switching of the pre-polarisation field have not been evaluated. We analysed these requirements numerically and estimated the magnetic resonance signal strength and image quality for two practical switching modes in an instrument suitable for scanning the human head. Von Mises stress analysis showed that although magnetic forces were significantly higher for two specific rungs, the structural integrity of magnet rungs would not be compromised. Our simulations suggest that a significantly higher signal yield is obtained by switching off the pre-polarisation field with the angular velocity in each rung dependent on its location.

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