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In-vivo and numerical analysis of the eigenmodes produced by a multi-level Tic-Tac-Toe head transmit array for 7 Tesla MRI.
- Source :
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PloS one [PLoS One] 2018 Nov 27; Vol. 13 (11), pp. e0206127. Date of Electronic Publication: 2018 Nov 27 (Print Publication: 2018). - Publication Year :
- 2018
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Abstract
- Radio-frequency (RF) field inhomogeneities and higher levels of specific absorption rate (SAR) still present great challenges in ultrahigh-field (UHF) MRI. In this study, an in-depth analysis of the eigenmodes of a 20-channel transmit Tic-Tac-Toe (TTT) RF array for 7T neuro MRI is presented. The eigenmodes were calculated for five different Z levels (along the static magnetic field direction) of the coil. Four eigenmodes were obtained for each Z level (composed of 4 excitation ports), and they were named based on the characteristics of their field distributions: quadrature, opposite-phase, anti-quadrature, and zero-phase. Corresponding finite-difference time-domain (FDTD) simulations were performed and experimental B1+ field maps were acquired using a homogeneous spherical phantom and human head (in-vivo). The quadrature mode is the most efficient and it excites the central brain regions; the opposite-phase mode excites the brain peripheral regions; anti-quadrature mode excites the head periphery; and the zero-phase mode excites cerebellum and temporal lobes. Using this RF array, up to five eigenmodes (from five different Z levels) can be simultaneously excited. The superposition of these modes has the potential to produce homogeneous excitation with full brain coverage and low levels of SAR at 7T MRI.<br />Competing Interests: Tiejun Zhao is employed by Siemens Medical Solutions. There are no patents or products in development to declare. This does not alter our adherence to PLOS ONE policies on sharing data and materials.
- Subjects :
- Cerebellum radiation effects
Electromagnetic Fields
Head diagnostic imaging
Head radiation effects
Humans
Magnetic Fields
Nasal Cavity diagnostic imaging
Nasal Cavity radiation effects
Phantoms, Imaging
Radio Waves
Temporal Lobe radiation effects
Cerebellum diagnostic imaging
Computer Simulation
Magnetic Resonance Imaging methods
Temporal Lobe diagnostic imaging
Subjects
Details
- Language :
- English
- ISSN :
- 1932-6203
- Volume :
- 13
- Issue :
- 11
- Database :
- MEDLINE
- Journal :
- PloS one
- Publication Type :
- Academic Journal
- Accession number :
- 30481187
- Full Text :
- https://doi.org/10.1371/journal.pone.0206127