Abstract
Semi-implantable bone conduction implants (BCI) and active middle ear implants (AMEI) for patients with sensorineural, conductive or mixed hearing loss commonly use an amplitude modulation technology to transmit power and sound signals from an external audio processor to the implant. In patients, the distance dependence of the signal amplitude is of minor importance as the skin thickness is constant and only varies between 3–7 mm. In this range, critical coupling transmission technique sufficiently reduces the variability in amplitude, but fails to provide well-defined amplitudes in many research and clinical applications such as intraoperative integrity tests where the distance range is exceeded by using sterile covers. Here we used the BCI Bonebridge (BB, Med-El, Austria) as an example to develop and demonstrate a system that synthesizes the transmission signal, determines the distance between the transmitter and the receiver implant coil and compensates transmission losses. When compared to an external audio processor (AP304) on an artificial mastoid, our system mainly decreased amplitude variability from over 11 dB to less than 3 dB for audio frequencies (0.1–10 kHz) at distances up to 15 mm, making it adequate for intraoperative and audiometric tests.
Highlights
The Bonebridge (Fig. 1, BB, MED-EL, Innsbruck, Austria) transcutaneous bone conduction implant (TBCI), recently certified and introduced to the market, is used to treat patients with conductive or mixed hearing loss[1]
With the TBCI on the artificial mastoid, the output vibration level of the implant driven with the AP 304 was compared to our developed transmission system with varying distances ranging from 0–15 mm between the respective transmitter and the implant coil housings
The acceleration output amplitude of the TBCI driven with the AP 304 showed (Fig. 6a) an average 11.0 ± 2.6 dB (mean value (MV) ± standard deviation (SD)) drop across frequencies between 0.1 and 10 kHz from the maximum amplitude when the distance between the AP 304 and receiver coil was increased from 0 to 15 mm
Summary
The Bonebridge (Fig. 1, BB, MED-EL, Innsbruck, Austria) transcutaneous bone conduction implant (TBCI), recently certified and introduced to the market, is used to treat patients with conductive or mixed hearing loss[1]. The demodulated audio signal stimulates the cochlea with bone vibration, bypassing the middle ear[2] For quantitative measurements such as those performed intraoperatively to verify the functionality of the implant or audiological testing, transmitting a well-characterized stimulus amplitude to the implant is required. The implant’s external processor transmission system is designed for daily use in patients with normal skin thickness of approximately 5 to 7 mm This distance between the audio processor and the implant should be kept less than 7 mm[3]. To transmit a well-defined stimulus, it was necessary to develop a transmission and measurement system that allows for output level compensation of the vibrator transducer output by estimating the unknown distance between the transmitter and the receiver implant coil as well as to compensate for attenuations. The input signal amplitude is adjusted to compensate for transmission losses arising from the distance, increasing the accuracy
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