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 cont raindicated for use in patients with pacemakers, cochlear implants, an d neurostimulators. Our semi-implantable middle ear device uses a new adhesive bone cement, 4-META/MMA-TBB, for cementation of a 29-mg titan ium-encased neodymium-iron-boron (NdFeB) magnet to the incus. Methods: Five NdFeB magnets and four solid titanium cylinders were cemented on to the incus of five preserved human temporal bones and two cadaver he ads. They were all inserted into a magnetic resonance imager and evalu ated for possible disruption. Results: Owing to the magnetic torque, t he three magnets on the temporal bone were disrupted from the incus. T he two cylinders on the temporal bones and the two cylinders and two m agnets on the whole heads were not affected. The magnetic resonance im aging field did nor affect the coercive force of the NdFeB magnets. Co nclusion: The large torque produced by a magnetic resonance imager may disrupt the magnet-cement and cement-incus interfaces, causing dislod gement. We postulate that patients with implantable magnets on the inc us should not undergo magnetic resonance imaging testing.