title: Assessment of magnetic field interactions and radiofrequency-radiation-induced heating of metallic spinal implants in 7 T field.
abstract: The safety of metallic spinal implants in magnetic resonance imaging (MRI) performed using ultrahigh fields has not been established. Hence, we examined whether the displacement forces caused by a static magnetic field and the heating induced by radiofrequency radiation are substantial for spinal implants in a 7 T field. We investigated spinal rods of various lengths and materials, a screw, and a cross-linking bridge in accordance with the American Society for Testing and Materials guidelines. The displacement forces of the metallic implants in static 7 T and 3 T static magnetic fields were measured and compared. The temperature changes of the implants during 15-min-long fast spin-echo and balanced gradient-echo image acquisition sequences were measured in the 7 T field. The deflection angles of the metallic spinal materials in the 7 T field were 5.0-21.0° [median: 6.7°], significantly larger than those in the 3 T field (1.0-6.3° [2.2°]). Among the metallic rods, the cobalt-chrome rods had significantly larger deflection angles (17.8-21.0° [19.8°]) than the pure titanium and titanium alloy rods (5.0-7.7° [6.2°]). The temperature changes of the implants, including the cross-linked rods, were 0.7-1.0°C [0.8°C] and 0.6-1.0°C [0.7°C] during the fast spin-echo and balanced gradient-echo sequences, respectively; these changes were slightly larger than those of the controls (0.4-1.1°C [0.5°C] and 0.3-0.9°C [0.6°C], respectively). All of the metallic spinal implants exhibited small displacement forces and minimal heating, indicating that MRI examinations using 7 T fields may be performed safely on patients with these implants. © 2016 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 35:1831-1837, 2017.
authors: Department of Orthopedic Surgery, School of Medicine, Iwate Medical University, 19-1 Uchimaru, Morioka, 020-8505, Japan.
authors: Itsuko
authors: I
authors: Tsukimura
authors: Department of Orthopedic Surgery, School of Medicine, Iwate Medical University, 19-1 Uchimaru, Morioka, 020-8505, Japan.
authors: Hideki
authors: H
authors: Murakami
authors: Division of Ultrahigh Field MRI, Institute of Biomedical Sciences, Iwate Medical University, Morioka, Japan.
authors: Makoto
authors: M
authors: Sasaki
authors: Department of Orthopedic Surgery, School of Medicine, Iwate Medical University, 19-1 Uchimaru, Morioka, 020-8505, Japan.
authors: Hirooki
authors: H
authors: Endo
authors: Department of Orthopedic Surgery, School of Medicine, Iwate Medical University, 19-1 Uchimaru, Morioka, 020-8505, Japan.
authors: Daisuke
authors: D
authors: Yamabe
authors: Department of Orthopedic Surgery, School of Medicine, Iwate Medical University, 19-1 Uchimaru, Morioka, 020-8505, Japan.
authors: Ryosuke
authors: R
authors: Oikawa
authors: Department of Orthopedic Surgery, School of Medicine, Iwate Medical University, 19-1 Uchimaru, Morioka, 020-8505, Japan.
authors: Minoru
authors: M
authors: Doita
mesh_terms: D000075202:Contraindications; D006801:Humans; D016268:Internal Fixators; D060526:Magnetic Fields / Q000009:adverse effects*; D008279:Magnetic Resonance Imaging / Q000009:adverse effects; D008670:Metals; D019637:Orthopedic Procedures / Q000295:instrumentation*; D013131:Spine / Q000601:surgery
chemical_list: D008670:Metals
keywords: 7 T; displacement; heating; metallic spinal implants; safety