A New Audiometric Bone Vibrator, Radioear B81, and the Bone Conduction Implant with Emphasis on Magnetic Resonance Imaging

University dissertation from Chalmers University of Technology

Abstract: Hearing by air conduction (AC) and bone conduction (BC) are attributed to be the natural ways of stimulating the cochlea. With AC hearing, the cochlea is stimulated by air pressure variations via the ear canal, whereas with BC hearing, sound vibrations are transmitted thru the skull bone to the cochlea. Sensorineural hearing losses are commonly rehabilitated with conventional AC hearing aids in the ear canal, but patients who are suffering from conductive or mixed hearing losses, and who are unable to use AC hearing aids, may instead use bone conduction devices (BCDs). In order to determine the type and degree of hearing loss, the BC hearing thresholds are measured using a bone vibrator, and then analyzed together with the AC hearing thresholds to suggest an appropriate rehabilitation alternative. This thesis deals with two BC hearing related topics. The first topic is evaluating a new audiometric bone vibrator, Radioear B81, which is assumed to offer more accurate BC hearing threshold measurements. The second topic is related to a new type of active transcutaneous BCD, called the Bone Conduction Implant (BCI), which leaves the skin intact by using a wireless solution that does not require a permanent skin penetration. Even though the applications are different, both devices use the same Balanced Electromagnetic Separation Transducer (BEST) principle as motor unit in their design. The audiometric bone vibrator Radioear B81 was found to have an improved low frequency performance and can produce higher output levels with less harmonic distortion than was possible before. In a clinical study of the first six patients, it was found that the BCI is a realistic alternative to already commercially available BCDs. In technical evaluations, the BCI was shown to be insensitive to skin thickness variations and to have robust output, and that it possibly tolerates magnetic resonance imaging at 1.5 Tesla.