Acronym: CIModelPLUS

Grant agreement ID: 702030

Funded under: H2020-EU.1.3.2.

Funding call: H2020-MSCA-IF-2015

Project Fellow: Dr. Siwei Bai

Project duration: 1 March 2017 – 28 February 2019

Objective

Cochlear implants (CIs) are proven effective in restoring hearing to the severe-to-profoundly deaf. Up to 2012, there were more than 100,000 CI users in Europe, which only accounts for 7% of all adult CI candidates. The most severe limitation of current CI technology is caused by the wide spread of electric current in the cochlea, which results in a poor spectral resolution of electrical stimulation of the nerve and limits the number of effective electrodes. Computational models of the cochlea have been used to facilitate the development of CIs. These models depend on the geometry of the reconstructed cochlea and the exact knowledge of the electrical impedances of different tissues. However, only crude estimation of the impedances of all media is available, and most computational models of the cochlea only adopted an ideal representation of the geometry.

Therefore, CIModelPLUS aims to provide engineers an advanced computational model of the cochlea with incorporated CI, which will show improved accuracy of the electric current distribution in the tissues, in order to facilitate the development of next-generation CIs. To fulfil this aim, computational models of cochleae will be reconstructed from the µ-CT scans of temporal bone specimens, and the electric current distribution inside the cochlea will also be measured experimentally. The simulation and experimental results will later be combined to develop the advanced computational model of the cochlea.

CIModelPLUS involves interdisciplinary research between engineering, physics, neuroscience and medicine, and intersectoral collaboration between academia and CI industry. It will lead to the future development of CIs due to the accurate and validated computational approach adopted, and the advancement of CI technology will improve the quality of life of over 100,000 current CI users and other CI candidates in Europe, as well as that of their families and the communities that they reside in.

Project Progress:

All milestones defined for CIModelPLUS have been reached.

A three-dimensional (3D) anatomically-accurate computer model of the human cochlea with imbedded CI electrode array was reconstructed based on a set of high-resolution micro-CT scans of a human temporal bone. Electric current distribution in the cochlea as a result of electrical stimulation from CI electrodes was simulated using this 3D cochlear model.

Three different tasks were performed to measure the electric current inside the cochlea, and the results were later used as a reference for optimising the computer model. Task 1 was to perform direct measurements of the electric potential within the cochlea of a temporal bone specimen by using an additional microelectrode. Task 2 was to directly visualise the electric current flow using a technique called current density imaging (CDI). It turned out that this method was not sensitive enough. We therefore conducted additional measurements (Task 3) where we measured electric potentials inside the cochlea of implanted patients using the implanted electrode. Task 3 was to directly measure the electric potential within the cochlea of CI recipients by using already-implanted CI electrodes, which was a non-invasive method applied to living human subjects. Subsequently, these measurements were used to optimise the electrical conductivity values of different tissues in the cochlear model. The influence of CI electrode positions on the electric current distribution in the cochlea was investigated using the optimised model.

Moreover, a semi-automated algorithm was developed to reconstruct the path created of auditory nerve fibres (ANFs) inside the cochlear model by searching for the shortest path between given starting and end points. In order to implement a biophysical model on the reconstructed ANFs, we conducted a systemic review of different models in the literature. We hope that based on the review, we will be able to select or create the optimal biophysical model to be implemented within our advanced computational model of human cochlea.

Preliminary results obtained within CIModelPLUS have been presented at major conferences and invited talks within the field of medical engineering and hearing research. Final results will be published at high-impact international journals with Open Access.

Public relations:

• 15x4 Talks: Medicine, Atomic video, Cochlea, Supramolecules. Hosted by 15x4 Munich and Marie Curie Alumni Association. Friedrich von Thiersch Hörsaal, Technical University of Munich, Munich, Germany

Invited talks:

• 3D Model of the Implanted Cochlea for the Study of Current Spread. Hörenseminar. October 2018. Hörzentrum München, Munich, Germany
• From Anatomical Images to Computer Models — 3D Computational Modelling for Bio-implants. May 2018. University of Hong Kong, Hong Kong

Conference presentations:

• 40^th International Conference of the IEEE Engineering in Medicine and Biology Conference. Oral presentation: Influence of the Cochlear Implant Electrode Array Placement on the Current Spread in the Cochlea. July 2018. Honolulu, US
• 44. Jahrestagung für Akustik. Poster presentation: Einfluss der Position des Elektroden-Arrays eines Cochlea-Implantats auf die Potentialverteilung in der Cochlea. March 2018. Munich, Germany
• 41^st Annual MidWinter Meeting of the Association for Research in Otolaryngology. Poster presentation: Activation Pattern of Auditory Nerve Fibres due to Cochlear Implant Stimulation: A Modeling Study. February 2018. San Diego, US
• 41^st Annual MidWinter Meeting of the Association for Research in Otolaryngology. Poster presentation: A High-Resolution Cochlear Model with Reconstructed Cochlear Nerve Fibres. February 2018. San Diego, US
• Conference on Implantable Auditory Prostheses. Poster presentation:  a biophysical model of the auditory nerve based on high-resolution microct scans. July 2017. Tahoe City, US
• Conference on Implantable Auditory Prostheses. Poster presentation:  Reconstruction of a high-resolution cochlear model for cochlear implant research. July 2017. Tahoe City, US

Journal Publications:

• R Bachmaier, J Encke, M Obando-Leiton, W Hemmert, S Bai. Comparison of multicompartment cable models of human auditory nerve fibres. (in preparation for Frontiers in Neuroscience)
• S Bai, J Encke, R Weiß, F Schäfer, F Böhnke, W Hemmert. Current distribution in the human cochlea: a computational study based on high-resolution µCT scans. (in preparation for Frontiers in Neuroscience)