Transimpedance Matrix (TIM) Measurement for the Detection of Intraoperative Electrode Tip Foldover Using the Slim Modiolar Electrode: A Proof of Concept Study

Abstract

Objectives: The aim of this study is to report on our preliminary experience with Transimpedance Matrix (TIM)measurement for the detection of cochlear implant electrode tip foldovers compared with intraoperative imaging in patients implanted with the slim modiolar electrode (SME). Study Design: Proof of concept study. Setting: Tertiary university referral center. Patients: Twenty five ears (in 22 patients) implanted consecutively with the SME. Intervention(s): Following cochlear implantation, intraoperative TIM-measurement and fluoroscopy were performed. One week postoperatively, the electrode position was evaluated using Computed Tomography (CT)-imaging. Main Outcome Measures: Electrode array tip foldover.Results: Electrode array tip foldover occurred in three of the 25 cochlear implantations performed (12%). In each case, the foldover was detected by both TIM and fluoroscopy, leading to reposition and correct intracochlear placement of the array. Conclusions: TIM-measurement is a promising method for the intraoperative detection of an electrode array tip foldover. The TIM-tool with intuitive heatmap display is easy to use, fast, and readily available to clinics using TIM-software in the operating theatre.

Analysis of Neural Interface When Using Modiolar Electrode Stimulation. Radiological Evaluation, Trans-Impedance Matrix Analysis and Effect on Listening Effort in Cochlear Implantation

“…The full set of electrical spread curves, when normalized by the current, is known as trans-impedance matrix (TIM). Several studies have demonstrated the utility of TIM and other voltage measurement algorithms [16,17] to identify the intra-cochlear electrode positioning. The proximity of the electrode to the modiolar wall may result in some variation in the tissue and fluid environment, and it is of interest to investigate the effect of the modiolar proximity, the measured transimpedance and the cognitive effort on pitch discrimination.…”

Variations in Microanatomy of the Human Modiolus: Implications for Cochlear Implants

“…This is probably intended to lean on the modiolus and prevent a foldover. Nonetheless, even experienced surgeons cannot prevent tip fold-over in all cochleae with this electrode 20,32,33 , indicating that this approach is not always successful.…”

“…Furthermore, perimodiolar placements require preformed electrode arrays 20,23 . These cannot be implanted in their precurved form, and even using a positioner (straightener or stylet) that straightens their form for implantation still involves the risk of a fold-over of the electrode array once it is released from the positioner 20,[31][32][33] or a scalar translocation 34 . No detailed analysis of the relation between the electrode and the modiolus and its interindividual variability has been published yet.…”

Variations in microanatomy of the human modiolus require individualized cochlear implantation

“…Furthermore, perimodiolar placements require preformed electrode arrays 21 , 24 . These cannot be implanted in their precurved form, and even using a positioner (straightener or stylet) that straightens their form for implantation still involves the risk of a fold-over of the electrode array once it is released from the positioner 21 , 32 – 34 or the risk of a scalar translocation 35 . In fact, a recent retrospective study on 1722 cochlear implantations reported that dependent on the electrode array that was implanted, tip fold-over rates may go up to 10.5% 33 .…”