Individual Optimization of the Insertion of a Preformed Cochlear Implant Electrode Array

Purpose. The aim of this study was to show that individual adjustment of the curling behaviour of a preformed cochlear implant (CI) electrode array to the patient-specific shape of the cochlea can improve the insertion process in terms of reduced risk of insertion trauma. Methods. Geometry and curling behaviour of preformed, commercially available electrode arrays were modelled. Additionally, the anatomy of each small, medium-sized, and large human cochlea was modelled to consider anatomical variations. Finally, using a custom-made simulation tool, three different insertion strategies (conventional Advanced Off-Stylet (AOS) insertion technique, an automated implementation of the AOS technique, and a manually optimized insertion process) were simulated and compared with respect to the risk of insertion-related trauma. The risk of trauma was evaluated using a newly developed “trauma risk” rating scale. Results. Using this simulation-based approach, it was shown that an individually optimized insertion procedure is advantageous compared with the AOS insertion technique. Conclusion. This finding leads to the conclusion that, in general, consideration of the specific curling behaviour of a CI electrode array is beneficial in terms of less traumatic insertion. Therefore, these results highlight an entirely novel aspect of clinical application of preformed perimodiolar electrode arrays in general

Three-dimensional histological specimen preparation for accurate imaging and spatial reconstruction of the middle and inner ear

PURPOSE:    This paper presents a highly accurate cross-sectional preparation technique. The research aim was to develop an adequate imaging modality for both soft and bony tissue structures featuring high contrast and high resolution. Therefore, the advancement of an already existing microgrinding procedure was pursued. The central objectives were to preserve spatial relations and to ensure the accurate three-dimensional reconstruction of histological sections. METHODS:    Twelve human temporal bone specimens including middle and inner ear structures were utilized. They were embedded in epoxy resin, then dissected by serial grinding and finally digitalized. The actual abrasion of each grinding slice was measured using a tactile length gauge with an accuracy of one micrometre. The cross-sectional images were aligned with the aid of artificial markers and by applying a feature-based, custom-made auto-registration algorithm. To determine the accuracy of the overall reconstruction procedure, a well-known reference object was used for comparison. To ensure the compatibility of the histological data with conventional clinical image data, the image stacks were finally converted into the DICOM standard. RESULTS:    The image fusion of data from temporal bone specimens’ and from non-destructive flat-panel-based volume computed tomography confirmed the spatial accuracy achieved by the procedure, as did the evaluation using the reference object. CONCLUSION:    This systematic and easy-to-follow preparation technique enables the three-dimensional (3D) histological reconstruction of complex soft and bony tissue structures. It facilitates the creation of detailed and spatially correct 3D anatomical models. Such models are of great benefit for image-based segmentation and planning in the field of computer-assisted surgery as well as in finite element analysis. In the context of human inner ear surgery, three-dimensional histology will improve the experimental evaluation and determination of intra-cochlear trauma after the insertion of an electrode array of a cochlear implant system

Eine strukturierte, biomechanische Analyse regenerativer und adaptiver Fähigkeiten des Knochens

Umbauvorgänge im Knochen werden in der Endoprothetik häufig als Störgröße und Hauptursache beschrieben, die zu aseptischen Lockerungen und somit Implantatversagen führen. Dem entgegen ist es Ziel des vorliegenden Buches, die adaptiven und regenerativen Fähigkeiten des Knochens als Potential für die Optimierung lasttragender Implantate darzulegen. Durch die strukturierte Aufbereitung der knocheninternen Gesetzmäßigkeiten – wie reparative Prozesse, adaptive Fähigkeiten, biomechanische und hydrodynamische Gestaltungsmerkmale einschließlich der Mechanismen der Mechanosensorik – werden diese für den konstruktiven Entwicklungsprozess zukünftiger Prothesensysteme zugänglich. Dadurch kann verbesserte knöcherne Integration und dauerhafte Verankerung durch die konsequente Ausnutzung der Dynamik des Knochens realisiert werden. Der darauf aufbauende Optimierungsprozess des Implantatdesigns folgt diesem biologisch-orientierten Ansatz und mündet im beispielhaften Konzept einer hydrodynamischen Hüftendoprothese. Deren Integration in die flüssigkeitsvermittelte Knochenphysiologie stellt eine grundlegende Neuerung in der bionisch inspirierten Endoprothetik dar und soll fehlgeleitete Umbauvorgänge im Knochen vermeiden.Teilw. zugl.: Ilmenau, Techn. Univ., Diplomarbeit, 200

Embankment Design in Seismic Areas — Indian Practice

A number of river valley projects for the development of water and power resources, particularly in the Northern and North Eastern part of India, lie on the foothills of Himalayas which is seismically active. In the developmental activity of dam building, aseismic design of dam is therefore recognized and adopted. The paper presents the current Indian practice in the aseismic design of embankment dams with illustrations from studies carried out on some recent dams

Identification of factors influencing insertion characteristics of cochlear implant electrode carriers

Insertion studies in artificial cochlea models (aCM) are used for the analysis of insertion characteristics of different cochlear implant electrode carrier (EC) designs by measuring insertion forces. These forces are summed forces due to the measuring position which is directly underneath the aCM. The current hypothesis is that they include dynamic friction forces during the insertion process and the forces needed to bend an initially straight EC into the curved form of the aCM. For the purposes of the present study, straight EC substitutes with a constant diameter of 0.7 mm and 20.5 mm intracochlear length were fabricated out of silicone in two versions with different stiffness by varying the number of embedded wires. The EC substitutes were inserted into three different models made of polytetrafluoroethylene (PTFE), each model showing only one constant radius. Three different insertion speeds were used (0.11 / 0.4 / 1.6 mm/s) with an automated insertion test bench. For each parameter combination (curvature, speed, stiffness) twelve insertions were conducted. Measurements included six full insertions and six paused insertions. Paused insertions include a ten second paused time interval without further insertion movement each five millimetres. Measurements showed that dynamic and static components of the measured summed forces can be identified. Dynamic force components increase with increased insertion speeds and also with increased stiffness of the EC substitutes. Both force components decrease with larger radius of the PTFE model. After the insertion, the EC substitutes showed a curved shape, which indicates a plastic deformation of the embedded wires due to the insertion into the curved models. The results can be used for further research on an analytical model to predict the insertions forces of a specific combination of selected parameters as insertion speed and type of EC, combined with given factors such as cochlear geometry

Force measurement at the insertion process of cochlear implant electrodes

Several research groups have reported studies on the insertion force measurement at different cochlear implant electrodes. So far, all experimental setups to measure the forces applied to the electrode outside the cochlea (inner ear), ie have measured externally. Our aim was to integrate the sensors into an automatically operating instrument insertion, so that the forces can be measured, which act directly on the electrode, ie an internal force measurement

Temporal bone phantom for decoupled cochlear implant electrode insertion force measurement

In research on cochlear implants, preclinical testing of newly developed electrode arrays and surgical tools is an essential procedure, which requires the availability of a suitable testing environment. For this purpose, human temporal bone specimens are most realistic, but their availability is limited and additional parameters such as insertion forces are hardly measurable. Therefore, the aim of this study was to develop a temporal bone phantom with realistic anatomical structures for intracochlear force measurement. The temporal bone was segmented from CBCT data of a human cadaver head. The segmented model was 3D printed with an additional artificial skin layer to enable the simulated use of surgical instruments such as a self-retaining retractor. A mechanically decoupled artificial cochlear model was realistically positioned within the temporal bone and was furthermore attached to a force sensor. The usability of the phantom was evaluated by performing automated EA insertions using an automated hydraulic insertion device. The experiments showed that the insertion forces within the cochlea could be measured without interferences from surrounding structures. Moreover, the artificial skin provided a rigid interface for the insertion tool. The new phantom is a realistic testing and training platform for cochlear implant electrode insertions with the advantage of measureable insertion forces

Toward automated cochlear implant insertion using tubular manipulators

During manual cochlear implant electrode insertion the surgeon is at risk to damage the intracochlear fine-structure, as the electrode array is inserted through a small opening in the cochlea blindly with little force-feedback. This paper addresses a novel concept for cochlear electrode insertion using tubular manipulators to reduce risks of causing trauma during insertion and to automate the insertion process. We propose a tubular manipulator incorporated into the electrode array composed of an inner wire within a tube, both elastic and helically shaped. It is our vision to use this manipulator to actuate the initially straight electrode array during insertion into the cochlea by actuation of the wire and tube, i.e. translation and slight axial rotation. In this paper, we evaluate the geometry of the human cochlea in 22 patient datasets in order to derive design requirements for the manipulator. We propose an optimization algorithm to automatically determine the tube set parameters (curvature, torsion, diameter, length) for an ideal final position within the cochlea. To prove our concept, we demonstrate that insertion can be realized in a follow-the-leader fashion for 19 out of 22 cochleas. This is possible with only 4 different tube/wire sets. © 2016 SPIE

Reducing the manual length setting error of a passive Gough-Stewart platform for surgical template fabrication using a digital measurement system

As recently demonstrated, a passive Gough-Stewart platform (a.k.a. hexapod) can be used to create a personalized surgical template to achieve minimally invasive access to the cochlea. The legs of the hexapod are manually adjusted to the desired length, which must be read off an analog scale. Previous experiments have shown that manual length setting of the hexapod's legs is error-prone because of the imprecise readability of the analog scale. The objective of this study is to determine if integration of a linear encoder and digitally displaying the measured length help reduce the length setting error. Two experiments were conducted where users set the leg length manually. In both experiments, the users were asked to set the leg length to 20 nominal values using the whole setting range from 0 mm to 10 mm. In the first experiment, users had to rely only on the analog scale; in the second experiment, the electronic display additionally showed the user the actual leg length. Results show that the mean length setting error without using the digital display and only relying on the analog scale was (0.036 ± 0.020) mm (max: 0.107 mm) in contrast to (0.001 ± 0.000) mm (max: 0.002 mm) for the experiment with the integrated digital measurement system. The results support integration of digital length measurement systems as a promising tool to increase the accuracy of surgical template fabrication and thereby patients' safety. Future studies must be conducted to evaluate if integration of a linear encoder in each of the six legs is feasible

A Tool to Enable Intraoperative Insertion Force Measurements for Cochlear Implant Surgery

Objective: Residual hearing preservation during cochlear implant (CI) surgery is closely linked to the magnitude of intracochlear forces acting during the insertion process. So far, these forces have only been measured in vitro. Therefore, the range of insertion forces and the magnitude of damage-inducing thresholds in the human cochlea in vivo remain unknown. We aimed to develop a method to intraoperatively measure insertion forces without negatively affecting the established surgical workflow. Initial experiments showed that this requires the compensation of orientation-dependent gravitational forces. Methods: We devised design requirements for a force-sensing manual insertion tool. Experienced CI surgeons evaluated the proposed design for surgical safety and handling quality. Measured forces from automated and manual insertions into an artificial cochlea model were evaluated against data from a static external force sensor representing the gold standard. Results: The finalized manual insertion tool uses an embedded force sensor and inertial measurement unit to measure insertion forces. The evaluation of the proposed design shows the feasibility of orientation-independent insertion force measurements. Recorded forces correspond well to externally recorded reference forces after reliable removal of gravitational disturbances. CI surgeons successfully used the tool to insert electrode arrays into human cadaver cochleae. Conclusion: The presented positive evaluation poses the first step towards intraoperative use of the proposed tool. Further in vitro experiments with human specimens will ensure reliable in vivo measurements. Significance: Intraoperative insertion force measurements enabled by this tool will provide insights on the relationship between forces and hearing outcomes in cochlear implant surgery