Impact of the Static and Radiofrequency Magnetic Fields Produced by a 7T MR Imager on Metallic Dental Materials

Oriso, Kenta; Kobayashi, Takuya; Sasaki, Makoto; Uwano, Ikuko; Kihara, Hidemichi; Kondo, Hisatomo

doi:10.2463/mrms.2014-0122

Cited by 24 publications

(20 citation statements)

References 19 publications

(19 reference statements)

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“…The measurements correspond well with those obtained in previous studies for dental and orthopedic implants made from the same materials 14, 15. These results indicate that the displacement forces on these implants in a 7 T field are minimal compared to gravity, although they are significantly larger than the displacement forces in a 3 T field.…”

Section: Discussionsupporting

confidence: 89%

“…In each assessment, the material being tested was suspended by a polyester thread (length 4–11 cm [median: 7.25 cm]; weight 0.002–0.003 mg [0.0025 mg]), and the deflection angle of the thread from the vertical line was visually measured using a protractor. These measurements were performed three times when the center of the materials was on the axis of the bore ( x = 0 cm, y = 0 cm) and at positions of 131 cm (7 T) and 85 cm (3 T) from the isocenter of the scanner, at which the deflection angles of metallic materials were the largest in our previous study, indicating the dB/dz is nearly the maximum value on the axis of the bore 14. The data obtained were then averaged.…”

Section: Methodsmentioning

confidence: 99%

“…These measurements were performed three times when the center of the materials was on the axis of the bore (x ¼ 0 cm, y ¼ 0 cm) and at positions of 131 cm (7 T) and 85 cm (3 T) from the isocenter of the scanner, at which the deflection angles of metallic materials were the largest in our previous study, indicating the dB/dz is nearly the maximum value on the axis of the bore. 14 The data obtained were then averaged.…”

Section: Magnetic-field-induced Deflection Testmentioning

confidence: 99%

“…For a 7 T magnetic field, the safety of various metallic implants must be revisited because metallic materials can experience unexpectedly strong attractive forces and heating due to the increased static magnetic field strength and RF radiation, respectively. A few reports have been published regarding this issue; however, the studies they described provided no information on spinal metallic implants in 7 T fields 14, 15, 16. Therefore, we investigated whether the displacement forces and heating of various spinal metallic implants are substantial in 7 T fields to ensure the safety of these implants during examinations using ultrahigh‐field MRI systems.…”

mentioning

confidence: 99%

“…A few reports have been published regarding this issue; however, the studies they described provided no information on spinal metallic implants in 7 T fields. [14][15][16] Therefore, we investigated whether the displacement forces and heating of various spinal metallic implants are substantial in 7 T fields to ensure the safety of these implants during examinations using ultrahigh-field MRI systems.…”

mentioning

confidence: 99%

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Assessment of magnetic field interactions and radiofrequency-radiation-induced heating of metallic spinal implants in 7 T field

et al. 2017

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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.

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Section: Discussionsupporting

confidence: 89%

Section: Methodsmentioning

confidence: 99%

Section: Magnetic-field-induced Deflection Testmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Assessment of magnetic field interactions and radiofrequency-radiation-induced heating of metallic spinal implants in 7 T field

et al. 2017

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Magnetic resonance imaging

MacDonald¹

2019

Oral and Maxillofacial Radiology

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Study of the radiofrequency‐induced heating inside the human head with dental implants at 7 T

Duan,

Wu,

Shi

et al. 2023

Bioelectromagnetics

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Conductive dental implants are commonly used in restorative therapy to replace missing teeth in patients. Ensuring the radiofrequency (RF) safety of these patients is crucial when performing 7 T magnetic resonance scans of their heads. This study aimed to investigate RF‐induced heating inside the human head with dental implants at 7 T. Dental implants and their attachments were fabricated and integrated into an anatomical head model, creating different measurement configurations (MCs). Numerical simulations were conducted using a 7 T transmit coil loaded with the anatomical head model, both with and without dental implants. The maximum temperatures inside the head for various MCs were computed using the maximum permissible input powers (MPIPs) obtained without dental implants and compared with published limits. Additionally, the MPIPs with dental implants were calculated for scenarios where the temperature limits were exceeded. The maximum temperatures observed inside the head ranged from 38.4°C to 39.6°C. The MPIPs in the presence of dental implants were 81.9%–97.3% of the MPIPs in the absence of dental implants for scenarios that exceeded the regulatory limit. RF‐induced heating effect of the dental implants was not significant. The safe scanning condition in terms of RF exposure was achievable for patients with dental implants. For patients with conductive dental implants of unknown configuration, it is recommended to reduce the input power by 18.1% of MPIP without dental implants to ensure RF safety.

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Impact of the Static and Radiofrequency Magnetic Fields Produced by a 7T MR Imager on Metallic Dental Materials

Cited by 24 publications

References 19 publications

Assessment of magnetic field interactions and radiofrequency-radiation-induced heating of metallic spinal implants in 7 T field

Assessment of magnetic field interactions and radiofrequency-radiation-induced heating of metallic spinal implants in 7 T field

Magnetic resonance imaging

Study of the radiofrequency‐induced heating inside the human head with dental implants at 7 T

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