Impact of the Characteristic Impedance of Coaxial Lines on the Sensitivity of a 750-MHz Electronically Tunable EPR Resonator
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A 750-MHz electronically tunable resonator was investigated in terms of the sensitivity of electron paramagnetic resonance (EPR) signal detection. The conversion efficiency of the radio-frequency magnetic field was calculated for resonators with 50- and 100-Ω coaxial coupling lines using three-dimensional (3D) microwave field and microwave circuit simulators. Based on the simulation results, two tunable resonators were physically constructed and compared in terms of EPR signal sensitivity using a nitroxyl radical solution. While the resonator with 100-Ω coaxial lines provided 14% greater signal intensity, its signal-to-noise ratio was lower than that of the resonator with 50-Ω lines. To demonstrate the capability of the constructed tunable resonator for EPR imaging experiments, a solution of nitroxyl radical and the leg of a tumor-bearing mouse were visualized.
The nitroxyl radical probe 2H,15N-DCP used in this study was kindly provided by Dr. Igor A. Kirilyuk, Novosibirsk Institute of Organic Chemistry, Novosibirsk, Russia. We appreciate Kumiko Yamamoto and Prof. Osamu Inanami at the Graduate School of Veterinary Medicine, Hokkaido University, for their help in the experiments with tumor-bearing mice. This work was supported in part by JSPS KAKENHI Grant numbers 26249057 and 16K12862.
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