TY - JOUR
T1 - Magnetic-Resonance-Based Electrical Property Mapping Using Global Maxwell Tomography with an 8-Channel Head Coil at 7 Tesla
T2 - A Simulation Study
AU - Giannakopoulos, Ilias I.
AU - Serralles, Jose E.C.
AU - Daniel, Luca
AU - Sodickson, Daniel K.
AU - Polimeridis, Athanasios G.
AU - White, Jacob K.
AU - Lattanzi, Riccardo
N1 - Funding Information:
This work was supported in part by the Skoltech-MIT Next Generation Program, by NIH R01 EB024536, and by NSF 1453675. It was performed under the rubric of the Center for Advanced Imaging Innovation and Research (CAI), a NIBIB Biomedical Technology Resource Center (NIH P41 EB017183).
Funding Information:
Manuscript received December 18, 2019; revised March 11, 2020; accepted April 28, 2020. Date of publication April 30, 2020; date of current version December 21, 2020. This work was supported in part by the Skoltech-MIT Next-Generation Program, the National Science Foundation (NSF 1453675) and in part by the National Institutes of Health (NIH R01EB024536, NIH P41EB017183). (Corresponding author: Ilias Giannakopoulos.) Ilias I. Giannakopoulos is with the Skoltech Center for Computational Data-Intensive Science and Engineering, Skolkovo Institute of Science and Technology, 143026 Moscow, Russia, and also with the Department of Electrical Engineering and Computer Science, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139 USA (e-mail: iliasgiannako@gmail.com).
Publisher Copyright:
© 1964-2012 IEEE.
PY - 2021/1
Y1 - 2021/1
N2 - Objective: Global Maxwell Tomography (GMT) is a recently introduced volumetric technique for noninvasive estimation of electrical properties (EP) from magnetic resonance measurements. Previous work evaluated GMT using ideal radiofrequency (RF) excitations. The aim of this simulation study was to assess GMT performance with a realistic RF coil. Methods: We designed a transmit-receive RF coil with 8 decoupled channels for 7T head imaging. We calculated the RF transmit field (B1+) inside heterogeneous head models for different RF shimming approaches, and used them as input for GMT to reconstruct EP for all voxels. Results: Coil tuning/decoupling remained relatively stable when the coil was loaded with different head models. Mean error in EP estimation changed from 7.5% to 9.5% and from 4.8% to 7.2% for relative permittivity and conductivity, respectively, when changing head model without re-tuning the coil. Results slightly improved when an SVD-based RF shimming algorithm was applied, in place of excitation with one coil at a time. Despite errors in EP, RF transmit field (B1+) and absorbed power could be predicted with less than 0.5% error over the entire head. GMT could accurately detect a numerically inserted tumor. Conclusion: This work demonstrates that GMT can reliably reconstruct EP in realistic simulated scenarios using a tailored 8-channel RF coil design at 7T. Future work will focus on construction of the coil and optimization of GMT's robustness to noise, to enable in-vivo GMT experiments. Significance: GMT could provide accurate estimations of tissue EP, which could be used as biomarkers and could enable patient-specific estimation of RF power deposition, which is an unsolved problem for ultra-high-field magnetic resonance imaging.
AB - Objective: Global Maxwell Tomography (GMT) is a recently introduced volumetric technique for noninvasive estimation of electrical properties (EP) from magnetic resonance measurements. Previous work evaluated GMT using ideal radiofrequency (RF) excitations. The aim of this simulation study was to assess GMT performance with a realistic RF coil. Methods: We designed a transmit-receive RF coil with 8 decoupled channels for 7T head imaging. We calculated the RF transmit field (B1+) inside heterogeneous head models for different RF shimming approaches, and used them as input for GMT to reconstruct EP for all voxels. Results: Coil tuning/decoupling remained relatively stable when the coil was loaded with different head models. Mean error in EP estimation changed from 7.5% to 9.5% and from 4.8% to 7.2% for relative permittivity and conductivity, respectively, when changing head model without re-tuning the coil. Results slightly improved when an SVD-based RF shimming algorithm was applied, in place of excitation with one coil at a time. Despite errors in EP, RF transmit field (B1+) and absorbed power could be predicted with less than 0.5% error over the entire head. GMT could accurately detect a numerically inserted tumor. Conclusion: This work demonstrates that GMT can reliably reconstruct EP in realistic simulated scenarios using a tailored 8-channel RF coil design at 7T. Future work will focus on construction of the coil and optimization of GMT's robustness to noise, to enable in-vivo GMT experiments. Significance: GMT could provide accurate estimations of tissue EP, which could be used as biomarkers and could enable patient-specific estimation of RF power deposition, which is an unsolved problem for ultra-high-field magnetic resonance imaging.
KW - Global Maxwell Tomography
KW - MR-based electrical property mapping
KW - RF shimming
KW - integral equations
KW - inverse scattering
KW - ultra-high-field magnetic resonance imaging
KW - Magnetic Resonance Spectroscopy
KW - Humans
KW - Radio Waves
KW - Equipment Design
KW - Magnetic Resonance Imaging
KW - Tomography
KW - Phantoms, Imaging
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U2 - 10.1109/TBME.2020.2991399
DO - 10.1109/TBME.2020.2991399
M3 - Article
C2 - 32365014
AN - SCOPUS:85084231279
SN - 0018-9294
VL - 68
SP - 236
EP - 246
JO - IRE transactions on medical electronics
JF - IRE transactions on medical electronics
IS - 1
M1 - 9082887
ER -