Multidisciplinary Approaches toward an Improved Efficacy of Cochlear Implants

Abstract

The cochlear implant (CI) is an auditory prosthesis that electrically stimulates the cochlear nerve to restore hearing. Although modern CI systems have proven to be a successful treatment for hearing impaired or deaf people, there are significant differences in the performance between people with normal hearing and CI recipients. This thesis aims to contribute to the field of cochlear implantation with a multidisciplinary approach, addressing problems related to minimally invasive surgical implantation and front-end processing of CI audio processors. First, concepts required for the clinical application of a minimally invasive robotic cochlear implantation approach were investigated. A computer-assisted method for scala tympani access and insertion trajectory planning was developed and evaluated in ex vivo models. With the proposed method, it was possible to achieve full scala tympani insertions in cases demanding a trajectory positioning accuracy below 0.5 mm. The study demonstrated that an optimal access to the scala tympani can be planned and performed with the robotic system. Furthermore, a manual insertion procedure for the minimally invasive approach was developed and tested. In all 8 tested specimens it was possible to insert the CI electrode arrays through the small drill tunnel using the proposed procedure, showing the feasibility of the approach. Second, front-end processing strategies of novel CI audio processors were evaluated. The influence of the microphone position of a single-unit processor on speech intelligibility in noise was investigated in a clinical study with 12 experienced CI users. It was shown that detrimental effects on speech reception are introduced by microphones positioned further to the back of the head. The signal-to-noise ratio was significantly better with the behind-the-ear processor when compared with the single-unit processor, if noise was presented from behind (4.4 dB, p <0.001). Directional microphone systems could be applied to overcome this drawback. A second audiological study with 10 subjects evaluated the expected benefit of a pinna effect imitating directional microphone system. The directional microphone setting improved the speech reception thresholds by up to 3.6 dB (p <0.01) on average when compared to the omnidirectional mode, indicating that CI users can benefit from the directional microphone system.