MRI Induced Torque and Demagnetization in Retention Magnets for a Bone Conduction Implant
Journal article, 2014

Performing magnetic resonance imaging (MRI) examinations in patients who use implantable medical devices involve safety risks both for the patient and the implant. Hearing implants often use two permanent magnets, one implanted and one external, for the retention of the external transmitter coil to the implanted receiver coil to achieve an optimal signal transmission. The implanted magnet is subjected to both demagnetization and torque, magnetically induced by the MRI scanner. In this paper, demagnetization and a comparison between measured and simulated induced torque is studied for the retention magnet used in a bone conduction implant (BCI) system. The torque was measured and simulated in a uniform static magnetic field of 1.5 T. The magnetic field was generated by a dipole electromagnet and permanent magnets with two different types of coercive fields were tested. Demagnetization and maximum torque for the high coercive field magnets was 7.7% +/- 2.5% and 0.20 +/- 0.01 Nm, respectively and 71.4% +/- 19.1% and 0.18 +/- 0.01 Nm for the low coercive field magnets, respectively. The simulated maximum torque was 0.34 Nm, deviating from the measured torque in terms of amplitude, mainly related to an insufficient magnet model. The BCI implant with high coercive field magnets is believed to be magnetic resonance (MR) conditional up to 1.5 T if a compression band is used around the skull to fix the implant. This is not approved and requires further investigations, and if removal of the implant is needed, the surgical operation is expected to be simple.

demagnetization

magnetic resonance (MR) safety

magnetic torque

Boneconduction implant (BCI)

Author

Karl-Johan Fredén Jansson

Chalmers, Signals and Systems, Signalbehandling och medicinsk teknik, Biomedical Signals and Systems

Bo Håkansson

Chalmers, Signals and Systems, Signalbehandling och medicinsk teknik, Biomedical Signals and Systems

Sabine Reinfeldt

Chalmers, Signals and Systems, Signalbehandling och medicinsk teknik, Biomedical Signals and Systems

Hamidreza Taghavi

Chalmers, Signals and Systems, Signalbehandling och medicinsk teknik, Biomedical Signals and Systems

Måns Eeg-Olofsson

University of Gothenburg

IEEE Transactions on Biomedical Engineering

0018-9294 (ISSN)

Vol. 61 6 1887-1893

Subject Categories

Otorhinolaryngology

DOI

10.1109/tbme.2014.2309978

PubMed

24845299

More information

Created

10/7/2017