Effect of magnetic resonance imaging on a new electromagnetic implantable middle ear hearing device

Objective: A 1.5-T magnetic resonance imager has been shown to be contraindicated for use in patients with pacemakers, cochLear implants, and neurostimulators. Our semi-implantable middle ear device uses a new adhesive bone cement. 4-META/MMA-TBB, for cementation of a 29-mg titaniumencased neodymium-iron-boron (NdFeB) magnet to the incus. Methods: Five NdFeB magnets and four solid titanium cylinders were cemented onto the incus of five preserved human temporal bones and two cadaver heads. They were all inserted into a magnetic resonance imager and evaluated for possible disruption. Results: Owing to the magnetic torque, the three magnets on the temporal bone were disrupted from the incus. The two cylinders on the temporal bones and the two cylinders and two magnets on the whole heads were not affected. The magnetic resonance imaging field did not affect the coercive force of the NdFeB magnets. Conclusion: The large torque produced by a magnetic resonance imager may disrupt the magnet-cement and cement-incus interfaces, causing dislodgement. We postulate that patients with implantable magnets on the incus should not undergo magnetic resonance imaging testing.