Multiple MRIs demagnetized an internal BAHA magnet – An enriching case for the everyday practice

Abstract

AbstractWe present a Baha patient with demagnetization after repeated magnetic resonance imagings (MRIs) and demonstrate a novel way of monitoring magnet adherence. A 53-year-old man with a Baha Attract System reported reduced holding force of the external audio processor after nine MRIs (eight at 1.5 T and one at 3 T). Subsequently, the original external magnet was replaced by a stronger magnet without benefit. After three additional MRIs at 1.5 T, a total loss of magnetic adherence was reported. During revision surgery replacing the internal magnet, we used three different methods to document the magnetic field of the old and new internal magnet; a gaussmeter, a flux detector film and in-situ determination of the minimum adhesive magnetic force. Measurements performed with the gaussmeter served as the gold standard and were confirmed by the other two methods. The application of MR imaging at 3 T in patients with a Baha system is off-label use and initiates magnetic-implant damage, while repeated MRI at 1.5 T scans seems to be harmless. To document potential demagnetization, a flux detector film can be used in daily practice due to its simplicity of application and broad availability.

Keywords

• Baha
• bone-anchored hearing aid
• demagnetization
• electromagnetic field
• MRI