Metamaterial Magnetic Sheet at 3.7-T MRI for Animal Imaging
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https://doi.org/10.1007/s11664-020-08512-0 2020 The Minerals, Metals & Materials Society
Metamaterial Magnetic Sheet at 3.7-T MRI for Animal Imaging HASSAN ALI
,1,4 XIN XU,2 and HAIBIN NI3
1.—University of Illinois at Urbana-Champaign Institute, Zhejiang University, Haining 314400, China. 2.—Ningbo Scientific Research and Design Institute of Environmental Protection, Liyuan South Road 219, Ningbo 315200, Zhejiang, China. 3.—Jiangsu Key Laboratory of Meteorological Observation and Information Processing, Nanjing University of Information Science and Technology, Nanjing 210044, China. 4.—e-mail: [email protected]
Animal models have been utilized for many decades to examine human diseases and symptoms via magnetic resonance imaging (MRI) techniques. To avoid the fatal effects of the strong static magnetic field (B0) when imaging the mouse brain at higher Tesla values in MRI, i.e., 7-T, we propose a compact metamaterial magnetic sheet which can improve the image resolution for simulation of the mouse brain even at lower Tesla values in MRI systems. The magnetic sheet operates at 3.7-T MRI working frequency and provides a passband within its interfaces to restore the formation of scattering of an evanescent radio-frequency (RF) field radiating from the MRI gradient coils towards the sheet. We show in the optimized simulated test bed setup that the magnetic sheet localizes and adjusts the response of the evanescent RF field and improves the transient transverse magnetic field B1 and signal-to-noise ratio at the designated region of interest, i.e., mouse brain (Mb), where B1 at the mouse brain is the response of the static magnetic field B0 generated by the magnetic resonance gradient coils. The unique concept proposed here is that negative permeability (l) controls the metamaterial magnetic sheet to improve image resolution inside the human brain without increasing B0 intensity at the brain, in order to avoid thermal heating of the brain tissues. Key words: MRI, magnetic materials, negative permeability, SRR, SAR
INTRODUCTION Metamaterials are utilized for multiple engineering applications,1,2 one of which is magnetic resonance imaging (MRI). It is observed that animal species like monkeys or mice possess anatomy similar to that of humans. Therefore, these animals are typically initially analyzed for clinical trials and investigations.3–7 Experiments reveal that MRI radiation perturbs the nuclei of the atoms in the biological tissue from equilibrium to a wobbling motion during tissue exposure to high static magnetic fields (B0). The formation of B0 around the gradient coils of the MRI unit generates transient transverse magnetic fields (B1) at magnetically
(Received June 8, 2020; accepted September 22, 2020)
exposed nuclei, and as a result, the nuclei change their spin energy level and become resonant at their Larmor frequency. This Larmor frequency is the frequency of resonance of nuclei which depends upon the gyromagnetic ratio of the nuclei, which is different for different nuclei (blood, brain, bones, flesh,
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