The Safety of Active Hearing Implants in the Ultra-high Field Magnetic Resonance Environment: A Pilot Study

This study aimed to evaluate the interactions of multiple active hearing implants in the 7T magnetic resonance (MR) environment by assessing interactions occurring between the implantable device and the MR environment. One cochlear implant and 2 bone conduction implant models were used in the study.

The use of MR techniques in patients with active hearing implants has become a daily practice at 1.5 and 3T. Scanners using field strengths of 7T are becoming more widely available and are likely to be associated with even greater patient risk.

Six potential interactions were investigated: magnetically induced force and torque, retaining magnet magnetization, device functionality, device heating, and image artifacts.

Device functionality was verified after 10 exposures. When no magnet was present, the force ratio, defined as the magnetically induced force divided by the force induced by gravity, remained below 0.3 for all devices. With the magnet in place, the force ratio increased to 11. Average magnetization changes measured were similar to the population spread at baseline. For all devices, heating did not exceed 0.35 °C compared with background heating after 15 minutes of consecutive scanning at 3.2 W/kg or with a gradient field strength of 41.8T/s.

The findings show no adverse effects or performance degradation of the implant within the predefined test conditions. Preliminary outcomes of this feasibility study are positive, yet do not imply implant safety in the 7T MR environment. Formal verification will be required to label a device safe at this field strength.