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Stability of the standard incus coupling of the Carina middle ear actuator after 1.5T MRI
Tijdschriftbijdrage - Tijdschriftartikel
Limited data is available concerning the safety of active middle ear implants (AMEI) duringMagnetic Resonance Imaging (MRI). Measurements in temporal bones are the gold standard for preclinical assessment of device safety. In this study the coupling stability of anactuator as used in a fully implantable AMEI was determined in temporal bones. Eleventemporal bones were implanted with the actuator according to the manufacturer’s surgicalguidelines. The actuator was coupled on the incus short process as recommended for sensorineural hearing loss. Temporal bones were exposed 10 times to the MRI magnetic fieldby entering the MRI suite in a clinically relevant way. Computed Tomography (CT) imageswere acquired before and after the experiment to investigate the risk of actuator dislocation.Based on the electrical impedance of the actuator, the loading of the actuator to the incuswas confirmed. Relative actuator displacement was determined on the CT images by comparing the initial with the final actuator position in 3D space. Impedance curves were analyzed after each exposure to check the loading of the actuator to the ossicles. Analysis ofCT images with a 0.30.6 mm in-plane resolution indicate no actuator displacement. Themaximum detected change in impedance for all actuators was 8.43 Ω at the actuator’s resonance frequency. Impedance curves measured when the actuator was retracted from theshort process after the experiment still indicate the presence of a clear resonance peak. Noactuator displacement or dislocation could be detected in the analysis of CT images and themeasured impedance curves. Impedance curves obtained when the actuator was retractedfrom the incus short process still show a clear resonance peak, indicating the device is stillfunctional after the MRI exposures.