Design and Fabrication of Compact Arrayed Magnet for Biological EPR Imaging
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Applied Magnetic Resonance
ORIGINAL PAPER
Design and Fabrication of Compact Arrayed Magnet for Biological EPR Imaging Hideo Sato‑Akaba1 · Yuki Okada2 · Kentaro Tsuji2 · Miho C. Emoto3 · Hirotada G. Fujii4 Received: 26 May 2020 / Revised: 4 August 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract A portable and compact electron paramagnetic resonance (EPR) imaging magnet was developed for building a 750 MHz EPR imaging system. To realize low-cost fabrication, it was shown that the magnetic homogeneity required for redox EPR imaging using nitroxyl probes can be approximately reproduced by regularly arranging small neodymium magnets that are easy to handle. A five-channel coil driver consisting of operational amplifiers and switching power supplies was developed for field sweep, field modulation, and three field gradients to downsize the imaging system. The EPR imaging of 4-oxo-2,2,6,6-tetramethylpiperidine-d16-1-oxyl (tempone-d16) using a phantom was successfully performed by employing a 3D radial sequence controlled by a digital EPR console.
1 Introduction Recently, a compact electron paramagnetic resonance (EPR) digital console has been developed for in vivo imaging of mouse [1, 2]. Replacing the analog signal processing by digital signal processing using a field-programmable gate array (FPGA) ICs can enhance the stability of measurement and ease of operation. Through the digital feedback control for reflection reduction, the decay rate of the nitroxyl radical in the head of the mouse can be visualized to evaluate the redox state of the brain [3, 4]. To obtain a 3D image of the decay rate, several 3D radial projection data sets are obtained with a temporal resolution of 9 s; this enabled the use of a six-membered * Hideo Sato‑Akaba [email protected]‑u.ac.jp 1
Department of Systems Innovation, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560‑8531, Japan
2
School of Engineering Science, Osaka University, Toyonaka, Osaka 560‑8531, Japan
3
Health Sciences University of Hokkaido, Sapporo, Hokkaido 002‑8072, Japan
4
Health Sciences University of Hokkaido, Ishikari, Hokkaido 061‑0293, Japan
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ring nitroxyl radical, which decays faster than a five-membered ring nitroxyl radical. This EPR console was operated using a commercial permanent magnet equipped with field sweep and XYZ gradient coils. However, most commercial EPR magnets used for in vivo imaging are large and heavy for a portable system. To realize a small portable magnet, an electromagnet with cylindrical coils has been developed and used for a tabletop EPR imaging system [5]. For a low-field MRI magnet, several arrayed magnets using small permeant magnets were reported to build a low-cost [6] and lightweight [7, 8] imaging system. As the magnetic field (less than 50 mT) of an L-band EPR imaging (EPRI) is weaker than that (several hundred mT) of a low-field MRI, the design of the arrayed magnet for the EPRI should be more feasible than that of the MR
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