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Gandji NP, Sica CT, Lanagan MT, et al. Displacement current distribution on a high dielectric constant helmet and its effect on RF field at 10.5 T (447 MHz). Magn Reson Med. 2021;86(6):3292-3303doi: 10.1002/mrm.28923.
Gandji, N. P., Sica, C. T., Lanagan, M. T., Woo, M. K., DelaBarre, L., Radder, J., Zhang, B., Lattanzi, R., Adriany, G., Ugurbil, K., & Yang, Q. X. (2021). Displacement current distribution on a high dielectric constant helmet and its effect on RF field at 10.5 T (447 MHz). Magnetic resonance in medicine, 86(6), 3292-3303. https://doi.org/10.1002/mrm.28923
Gandji, Navid P, et al. "Displacement current distribution on a high dielectric constant helmet and its effect on RF field at 10.5 T (447 MHz)." Magnetic resonance in medicine vol. 86,6 (2021): 3292-3303. doi: https://doi.org/10.1002/mrm.28923
Gandji NP, Sica CT, Lanagan MT, Woo MK, DelaBarre L, Radder J, Zhang B, Lattanzi R, Adriany G, Ugurbil K, Yang QX. Displacement current distribution on a high dielectric constant helmet and its effect on RF field at 10.5 T (447 MHz). Magn Reson Med. 2021 Dec;86(6):3292-3303. doi: 10.1002/mrm.28923. Epub 2021 Jul 17. PMID: 34272898.
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Magn Reson Med. 2021 Dec;86(6):3292-3303. doi: 10.1002/mrm.28923. Epub 2021 Jul 17.

Displacement current distribution on a high dielectric constant helmet and its effect on RF field at 10.5 T (447 MHz).

Magnetic resonance in medicine

Navid P Gandji, Christopher T Sica, Michael T Lanagan, Myung-Kyun Woo, Lance DelaBarre, Jerahmie Radder, Bei Zhang, Riccardo Lattanzi, Gregor Adriany, Kamil Ugurbil, Qing X Yang

Affiliations

  1. Center for NMR Research, Departments of Neurosurgery and Radiology, College of Medicine, Pennsylvania State University, Hershey, Pennsylvania, USA.
  2. Department of Engineering Science and Mechanics, Pennsylvania State University, State College, Pennsylvania, USA.
  3. Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
  4. UT Southwestern Medical Center, Advance Imaging Research Center, Dallas, Texas, USA.
  5. Center for Advanced Imaging Innovation and Research (CAI2R) and Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.

PMID: 34272898 DOI: 10.1002/mrm.28923

Abstract

PURPOSE: Investigating the designs and effects of high dielectric constant (HDC) materials in the shape of a conformal helmet on the enhancement of RF field and reduction of specific absorption rate at 10.5 T for human brain studies.

METHODS: A continuous and a segmented four-piece HDC helmet fit to a human head inside an eight-channel fractionated-dipole array were constructed and studied with a phantom and a human head model using computer electromagnetic simulations. The simulated transmit efficiency and receive sensitivity were experimentally validated using a phantom with identical electric properties and helmet-coil configurations of the computer model. The temporal and spatial distributions of displacement currents on the HDC helmets were analyzed.

RESULTS: Using the continuous HDC helmet, simulation results in the human head model demonstrated an average transmit efficiency enhancement of 66%. A propagating displacement current was induced on the continuous helmet, leading to an inhomogeneous RF field enhancement in the brain. Using the segmented four-piece helmet design to reduce this effect, an average 55% and 57% enhancement in the transmit efficiency and SNR was achieved in human head, respectively, along with 8% and 28% reductions in average and maximum local specific absorption rate.

CONCLUSION: The HDC helmets enhanced the transmit efficiency and SNR of the dipole array coil in the human head at 10.5 T. The segmentation of the helmet to disrupt the continuity of circumscribing displacement currents in the helmet produced a more uniform distribution of the transmit field and lower specific absorption rate in the human head compared with the continuous helmet design.

© 2021 International Society for Magnetic Resonance in Medicine.

Keywords: SAR reduction; SNR enhancement; high dielectric constant material; ultrahigh-field MRI

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