Magnetic resonance imaging safety of the floating mass transducer.

HYPOTHESIS

The goals of this study are to observe 1.5-T magnetic resonance imaging (MRI)-related changes to the Vibrant Soundbridge floating mass transducer (FMT) magnetization, function, and position in different coupling modes within the middle ear; changes to middle ear structures; and effects on the transfer function to the inner ear.

BACKGROUND

The MRI safety of implantable hearing devices is important in daily routine clinical care as well as in urgent care.

METHODS

Nine FMTs were repeatedly investigated before and after MRI scanning. Changes in the position of the FMT (round window, incus, and stapes) and in the ossicular chain in temporal bones were estimated by microscopy, microendoscopy, and flat panel angiography. Functional investigations of the FMT in different coupling modes were done using laser Doppler vibrometry.

RESULTS

Qualitative demagnetization could be ruled out in all specimens after up to 11 MRI scans. In FMT couplings to the long process of the incus (n = 18), positional changes were found in 5 temporal bones. A disarticulation or exarticulation of the ossicles was not observed. Mean laser Doppler vibrometry measurements showed MRI-related changes in the stapes velocity. In FMT couplings to the round window (n = 23), we observed a fixation-dependent influence of MRI scanning on the FMT position and mean transfer function.

CONCLUSION

The functional integrity of the FMT was not significantly influenced after multiple MRI scans. Positional changes of the FMT within the middle ear are possible, but we observed no structural damage to middle ear structures. Effects on the transfer function are possible.