Intraoperative stimulation and measurement system for the Bonebridge with distance compensationDieses Projekt wurde vom DFG Cluster of Excellence EXC 1077/1 "Hearing4all" unterstützt.
23 April 2019 (online)
The transmission loss in analogue systems such as Bonebridge (MED-EL, Innsbruck, Austria) due to larger distances > 10 mm between the audio processors and the implant as it may occur in intraoperative stimulation causes increased inter-individual variability. We developed an inductive link to transmit a calibrated stimulus of known signal amplitude to the Bonebridge implant.
The change of the mutual inductance in the primary coil due to coupling coefficient changes was used to measure the distance between the transmitter and receiver coils. In a range between 2 to 17 mm the transmission losses were measured with the Bonebridge Floating Mass Transducer (BC-FMT) on an artificial mastoid (B&K, type 4935) with the Audio Processor 304 (AP304) and our stimulation device with/without compensation using the estimated distance.
The acceleration output amplitude of the Bonebridge driven with the AP304 showed 10 to 20 dB drop between 0.1 and 10 kHz when the distance between the AP304 and receiver coil increased from 2 to 17 mm. The acceleration amplitude of the Bonebridge driven with the developed transmission system showed up to 17 dB drop in the same frequency range. In contrast the compensated acceleration amplitude of BC-FMT driven with the developed system showed < 3 dB variations in the same distance range.
The new transmission system provides a well-characterized stimulus to the Bonebridge by estimating the distances between the transmitter and receiver coils and applying the compensation.