Cochlear Model for the Evaluation of MRI Sequences and Cochlear Implant Electrode Pattern at 3T

Introduction Cochlear implant (CI) magnets and surgical techniques (e.g., positioning) have made an impact on the relationship between CI and magnetic resonance imaging (MRI) by solving the problem of pain and artifact. Recent investigations displayed the possibility to evaluate the CI electrode position by MRI in vivo. However, further improved perceptual quality is needed to allow an improved evaluation of the electrode. Aims The aim of this study was to assess a cochlear model for the examination of CI electrode pattern and MRI sequences in vitro. Materials and Methods We investigated CI electrodes in a fluid-filled three-dimensional artificial scala tympani model combined with a fluid package in a 3T MRI scanner. Different high-resolution T2 sequences (0.6–0.2 mm voxel size) were used for the visual electrode pattern evaluation for finding an optimized sequence. Results Artificial models can be used to evaluate MRI characteristics of CI electrodes. In our scanner configuration, a 0.3 mm voxel and 0.9 mm slice thickness sequence showed the best compromise between resolution and scanning time. Conclusion and Significance MRI model-based testing can be performed in vitro to evaluate CI electrodes’ pattern and to optimize sequences. An MRI model is a tool for in vitro testing of MRI sequences and might help for future in vivo applications.

A Capacitive Cochlear Implant Electrode Array Sensing System to Discriminate Fold-Over Pattern

Purpose During insertion of the cochlear implant electrode array, the tip of the array may fold back on itself and can cause serious complications to patients. This article presents a sensing system for cochlear implantation in a cochlear model. The electrode array fold-over behaviors can be detected by analyzing capacitive information from the array tip. Method Depending on the angle of the array tip against the cochlear inner wall when it enters the cochlear model, different insertion patterns of the electrode array could occur, including smooth insertion, buckling, and fold-over. The insertion force simulating the haptic feedback for surgeons and bipolar capacitance signals during the insertion progress were collected and compared. The Pearson correlation coefficient (PCC) was applied to the collected capacitive signals to discriminate the fold-over pattern. Results Forty-six electrode array insertions were conducted and the deviation of the measured insertion force varies between a range of 20% and 30%. The capacitance values from electrode pair (1, 2) were recorded for analyzing. A threshold for the PCC is set to be 0.94 that can successfully discriminate the fold over insertions from the other two types of insertions, with a success rate of 97.83%. Conclusions Capacitive measurement is an effective method for the detection of faulty insertions and the maximization of the outcome of cochlear implantation. The proposed capacitive sensing system can be used in other tissue implants in vessels, spinal cord, or heart.

Minimizing Intracochlear Pressure: Influence of the Insertion Sheath

Objective: Atraumatic cochlear implantation (CI) and insertion of the electrode in particular are major goals of recent CI surgery. Perimodiolar electrode arrays need a stylet or exosheath for insertion. The sheath can influence the intracochlear pressure changes during insertion of the electrode. The aim of this study was to modify the insertion sheath to optimize intracochlear pressure changes. Methods: In an artifical cochlear model, 7 different modified insertion sheaths were used. The intracochlear pressure was measured with a micro-optical sensor in the apical part of the model cochlea. Results: Significant lower intracochlear pressure changes were observed when the apical part of the insertion sheath was either shortened or tapered. Modification of the stopper does influence the intracochlear pressure significantly. Conclusion: Modification of the insertion sheath leads to lower intracochlear pressure gain. The differences and impact on intracochlear pressure changes found in this study underline the importance of even subtle modifications of the electrode insertion technique.