DNP-MRI is the special imaging system for free radical and redox state in vivo. This imaging system is MRI scanning of H₁ spins with DNP(Dynamic Nuclear Polarization) after excitation unpaired electron spins in the radical. This system is useful for the study of oxidant stress disease in vivo. DNP-MRI use electron spin excitation. Using high magnetic field for high sensitivity and high resolution, excitation RF plus has very high frequency. At 0.3T electron spin excitation frequency is very high (8.4GHz). Because of limited penetration depth of radio frequency, there is the serious problem that is inhomogeneously excited of electron spins in vivo. Therefore the field cycle method is suggested as solution to turn down the main magnetic field only during electron excitation. This method has several ways, for example, “magnetic field switching using the electric magnet” or “sample transportation between two permanent magnets”.₁However for clinical application, “magnetic field switching using the electric magnet” is limited by FOV, and “sample transportation between two permanent magnets” is limited by human being transportation at a slow speed. We developed New "field cycle MRI system with rotary magnet" which has 300mT and 13.5mT magnets on a circle. Main magnetic field increase and decrease by Rotation two magnets on a circle.

Based on the experience from “sample transportation between two permanent magnets” magnetic field cycle method, we assemble and the magnets, the rotational mechanism, the console system and so on. into the system in Kyushu university. The magnets: commercialized permanent magnet (0.3T) for MRI, and circular arc-like permanent magnet for ESR excitation were produced by NOEMAX ENGENEERING Co., LTD. The rotational mechanism were produced and tuned by FUJI ELECTRIC CO., LTD. and MEIKO Co., LTD.. The console were produced by Japan Redox Limited. MRI resonator has internal ellipsoidal space (64mm*125mm).There are some problems attributed to magnet rotation. Therefore we refine and tune this system.In fig.3, we show the static and rotational images for the spherical phantom. Magnet rotational period is 3.0017±0.0002s, and velocity at magnet center is 838mm/s. (Condition: self-produced spherical phantom outer diameter 39.3mm, CuSO4 5mM with milli-Q; Spin Echo, NMR Freq. 12.48MHz, TR 3000ms, TE 7ms, FA 90, FOV 48mm*48mm, Slice 100mm, average 1, Acq. Band Width 25kHz, Acq. Num 64, Phase Encode 64, T=3s) Some problems attributed to magnet rotation are mismatched shimming, eddy current, induced electromotive force, and so on. Therefore we refine system and tune several imaging parameters. we get static image’s SNR=35.2, rotational image’s SNR23.6. SNR decrese attributed to magnet rotation is about 30%. New "field cycle MRI system with rotary magnet" is useful for DNP-MRI.