Assistive tool for cochlear implant fitting: Estimation and monitoring of the effective stimulation thresholds

One of the key factors for successful cochlear implantation is the correct fitting of the stimulation values. Once the cochlear implant is activated, obtaining a fitting that maximizes chances of complete rehabilitation is a long and difficult task, especially in the case of pediatric patients. Fitting protocols and principles vary from one specialist to another. Based on the experience gained through fitting of more than 150 patients, the paper introduces a new derived fitting parameter, the Effective Stimulation Threshold (EST), which represents the stimulation level evoking conscious hearing sensations to the patient upon free field sound stimulation. The paper also introduces the methodology to compute EST levels and presents preliminary observations on its importance and long term evolution. To help fitting procedures, the methodology is implemented by a software tool that loads the history of the maximum comfortable levels (MCL), threshold levels (THR), Maplaw settings and all registered audiograms, and computes the evolution of the EST levels of each individual electrode. Using the current EST levels, the newly registered audiograms and the intended new fitting settings introduced by the fitting specialist, the software predicts changes in the threshold hearing levels shown by the audiogram. The proposed solution is designed for MED-EL's Maestro Cochlear Implant system. However the presented concepts can be easily adapted to other cochlear implants.