The development of a procedure for the measurement of insertion depth angles of cochlear implant electrode arrays based on flat-panel computed tomography (FPCT) and the application of this technique to in vivo postoperative images. The knowledge of the insertion depth angle of electrode arrays is relevant for the preservation of low-frequency residual hearing and for optimizing speech coding strategies. Until now, the angular position of electrodes was derived from 2-dimensional radiographs. In the present study, 3-dimensional (3D) radiographs provided by FPCT were used to determine the insertion depth according to angular electrode positions with higher accuracy. For this purpose, a new evaluation procedure was designed and applied to radiographs of 15 cochlear implant patients. In contrast to 2-dimensional radiographs, the obtained 3D images show all 3 semicircular channels and therefore allow the determination of a clear reference, which is required for precise insertion angle measurements. Furthermore, the presented FPCT radiographs visualize distinct electrodes. Despite the constant length of the implanted electrode arrays, we have found a considerable variation of measured insertion depth angles, which is consistent with published observations on the variability and the gender dependence of the size of human cochleae. FPCT provides 3D high-resolution radiographic data that enable the determination of the insertion depth angle with high accuracy and, potentially, an angle determination of individual electrodes. Therefore, this low-dose technique is especially appropriate for postoperative investigations after cochlea implantation.

Hypothesis The aim of the study is to investigate the insertion depth angles for different types of electrode arrays and its variability depending on the individual cochlear size. Background Preoperative estimation of the insertion depth angles for different electrode arrays can help surgeons choose the optimal electrode length, especially for low-frequency residual hearing preservation. Methods Four different electrode arrays varying in lengths (20, 24, 28, and 31 mm) were inserted in 10 temporal bones to quantify the insertion depth angle of each inserted electrode. High-resolution 3D radiographs provided by Flat Panel Computed Volume Tomography (FPCT) were used to determine electrode array insertion depth angle and diameter of the cochlea’s basal turn. Results The high-resolution FPCT images from all electrode arrays inserted into the temporal bones allowed reliable measurements of insertion depth angles. In particular, statistically significant different insertion depth angles between the various array types were identified. The insertion of the 20-, 24-, 28-, and 31-mm arrays yielded a mean insertion depth angle of 341 degrees (SD, 22 degrees), 477 degrees (SD, 36 degrees), 587 degrees (SD, 42 degrees), and 673 degrees (SD, 38 degrees), respectively. Furthermore, a statistically significant negative correlation between insertion depth angle and diameter of the cochlea’s basal turn was found for the 20- and 31-mm arrays. Conclusion The results suggest an individually adapted length of electrode arrays, which should be taken into account for an improved decision paradigm for patients scheduled for cochlear implantation. This is of particular importance for patients with low-frequency residual hearing.

Objective: To develop an algorithm, based on the voltage matrix, for detecting regular cochlear implant (CI) electrode position during the implantation procedure, tip fold-over or basal kinking for lateral-wall electrodes. The availability of an algorithm would be valuable in clinical routine, as incorrect positioning of the electrode array can potentially be recognized intraoperatively. Design: In this retrospective study, intraoperative voltage matrix and postoperative digital volume tomography of 525 CI recipients were analyzed. On the basis of these data an algorithm was developed for detecting various kinds of electrode misplacements. Results: Seven incorrect electrode positions, three tip fold (0.57%) and four basal kinking (0.76%) were detected. For detecting correct positioning, a sensitivity of 100%, a specificity of 83.3%, and a positive predictive value (PPV) of 99.8% were found. For detecting tip fold-over, a sensitivity of 100%, a specificity of 100%, and a PPV of 100% were found. For detecting basal kinking, a sensitivity of 66%, a specificity of 100%, and a PPV of 100% were determined. Conclusion: The algorithm was found to be an effective screening tool for detecting tip fold-over or basal kinking.

To determine the relation between stapedius reflex thresholds in cochlear implant users evoked once through direct electric stimulation on single channels (ESRT) and once through acoustic stimulati...

ObjectiveThe goal of this study was to determine open field stapedius reflex thresholds (oSRTs) in CI patients with fittings based on subjective loudness ratings. A further objective was to compare these oSRTs and those of eSRT-based fittings that are similar to the oSRTs of normal hearing.DesignImpedance measurements of the ear drum were taken while subjects were wearing their audio processors. The stapedius reflex was elicited by electrical stimulation transmitted through the activated CI system in response to an acoustic stimulus presented in the free sound field.Study sampleSubjects were 50 experienced CI users (n = 57 ears) with CI fittings based on subjective loudness scaling.ResultsA reference range for the oSRTs was defined that was identified in CI patients with eSRT-based fittings. Sound levels for stapedius reflex detection were inside the reference target range in 70% of the cases, below the reference range (i.e. down to 40 dB HL) in 20% of the cases, and above the reference range in 10% of the cases.ConclusionStapedius reflex detection in a free sound field may help detect fittings with too high or too low stimulation levels that might reduce audiological performance.