Cochlear implant with a non-removable magnet: preliminary research at 3-T MRI

• Published in: European radiology Vol. 23; no. 6; pp. 1510 - 1518
• Main Authors: Dubrulle, F., Sufana Iancu, A., Vincent, C., Tourrel, G., Ernst, O.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-06-2013; Springer Nature B.V
• Subjects: Cochlear Implantation - instrumentation; Cochlear Implantation - methods; Cochlear Implants; Contraindications; Diagnostic Radiology; Electronics; Equipment Design; Head and Neck; Humans; Imaging; Internal Medicine; Interventional Radiology; Magnetic fields; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Magnets; Materials Testing; Medicine; Medicine & Public Health; Neuroradiology; Otology; Prosthesis Design; R&D; Radiology; Research & development; Temperature; Transplants & implants; Ultrasound; France; Cochlear implants; Adverse effects; Magnetic resonance imaging; Magnetic fields; Contraindications
• ISSN: 0938-7994; 1432-1084
• DOI: 10.1007/s00330-012-2760-3

Objective
To perform preliminary tests in vitro and with healthy volunteers to determine the 3-T MRI compatibility of a cochlear implant with a non-removable magnet.
Methods
In the in vitro phase, we tested six implants for temperature changes and internal malfunctioning. We measured the demagnetisation of 65 internal magnets with different tilt angles between the implant’s magnetic field (bi) and the main magnetic field (b0). In the in vivo phase, we tested 28 operational implants attached to the scalps of volunteers with the head in three different positions.
Results
The study did not find significant temperature changes or electronic malfunction in the implants tested in vitro. We found considerable demagnetisation of the cochlear implant magnets in the in vitro and in vivo testing influenced by the position of the magnet in the main magnetic field. We found that if the bi/b0 angle is <90°, there is no demagnetisation; if the bi/b0 angle is >90°, there is demagnetisation in almost 60 % of the cases. When the angle is around 90°, the risk of demagnetisation is low (6.6 %).
Conclusion
The preliminary results on cochlear implants with non-removable magnets indicate the need to maintain the contraindication of passage through 3-T MRI.
Key Points
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Magnetic resonance imaging can affect cochlear implants and vice versa.
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Demagnetisation of cochlear implant correlates with the angle between bi and b0.
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The position of the head in the MRI influences the demagnetisation.
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Three-Tesla MRI for cochlear implants is still contraindicated.
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However some future solutions are discussed.