Thomas S. Rau

Force measurement of insertion of cochlear implant electrode arrays in vitro: comparison of surgeon to automated insertion tool

Conclusions: We have demonstrated that an automated insertion tool (i.e. a robot) can be used to duplicate a complex surgical motion in inserting cochlear implant (CI) electrode arrays via the ‘advance-off-stylet’ (AOS) technique. As compared with human operators, the forces generated by the robot were slightly larger but the robot was more reliable (i.e. less force maxima). Objectives: We present force data collected during CI electrode insertion by human operators and by an automated insertion tool. Materials and methods: Using a three-dimensional, anatomically correct, translucent model of the scala tympani chamber of the cochlea, CI electrodes were inserted either by one of three surgeons (26 insertions) or by the robotic insertion tool (8 insertions). Force was recorded using a load beam cell calibrated for expected forces of <0.1 Newtons (N). The insertions were also videotaped to allow correlation of force with depth of penetration into the cochlea and speed of insertion. Results: Average insertion force used by the surgeons was 0.004±0.001 N and for the insertion tool it was 0.005±0.014 N (p<0.00001, Students t test). While the average insertion force of the automated tool was larger than that of the surgeons, the surgeons did have intermittent peaks during the AOS component of the insertion (between 120° and 200°).

Demagnetization of Cochlear Implants and Temperature Changes in 3.0T MRI Environment

Objective To investigate the level of demagnetization of the magnets and temperature changes in cochlear implants (Cis) in a 3.0 tesla (3.0T) MRI. Study Design Experimental. Subjects and Methods Demagnetization and remagnetization measurements were done on magnets for different types of CIs. Temperature of different body and electrode sides was measured in the MRI environment. Results Demagnetization of the magnets of the CI is dependent on the angle between the magnetic field of the CI magnet and the MRI. When this angle was greater than 80 degrees, relevant demagnetization occurred and sufficient remagnetization was not possible with the 3.0T MRI magnet. Maximum temperature rise was 0.5°C. Conclusions Patients carrying CIs with non-removable magnets should not enter a 3.0T MRI device in a routine clinical setup. Under special conditions (angle between the two magnets less than 80 degrees) imaging in a 3.0T MRI may be possible without harming the patient or the implant.

Artifacts caused by cochlear implants with non-removable magnets in 3T MRI: phantom and cadaveric studies.

The aim of this study was to evaluate artifacts produced by cochlear implants (CI) during 3.0 Tesla (T) magnetic resonance imaging of the brain using different sequences on phantom and cadaveric specimens. A phantom and three cadaveric specimens with CIs were imaged using a 3.0 T clinical scanner. Artifacts were analyzed quantitatively and according to the sequence used. Different brain regions were evaluated for image distortion and limitation of diagnostic significance. In cadaver studies, all sequences generated signal-void areas around the implant. In T2-weighted sequences, additional periodic shadowing was discovered. Anatomical structures of the brain on the contralateral side of the CI were for the most part undistorted. At 3T, artifacts around CIs with non-removable magnets compromise image quality of the nearby brain regions and diagnosis of brain lesions is limited. In the contralateral hemisphere, diagnostic accuracy is only marginally limited.

An automated insertion tool for cochlear implants: another step towards atraumatic cochlear implant surgery

PurposeAtraumatic electrode insertion has been identified to be a crucial step for the preservation of residual hearing abilities, which allows hybrid electro-acoustic stimulation (EAS). The authors propose a tool for automation of the insertion process to achieve this.MethodsGeneral benefits as well as concept and design of an automated insertion tool are presented. Thirty insertions of Nucleus 24 Contour Advance Practice Electrodes in an artificial scala tympani model as well as 20 insertions in a human cochlea specimen were performed using the tool, implementing the AOS technique. For both studies, the achieved insertion depth angle was evaluated by photographic or X-ray documentation.ResultsThe mean achieved insertion depth angle was 410° for the lubricated model and 330° for the human cochlea specimen.ConclusionThe automated insertion tool has proven its capability to perform electrode insertions with final insertion depth angles within the target range of a standard cochlear implant surgery. Additionally, to the knowledge of the authors, it represents the only possibility to automatically insert cochlear implant electrodes via minimally invasive approaches.

Design of a Tool Integrating Force Sensing With Automated Insertion in Cochlear Implantation

The quality of hearing restored to a deaf patient by a cochlear implant in hearing preservation cochlear implant surgery (and possibly also in routine cochlear implant surgery) is believed to depend on preserving delicate cochlear membranes while accurately inserting an electrode array deep into the spiral cochlea. Membrane rupture forces, and possibly, other indicators of suboptimal placement, are below the threshold detectable by human hands, motivating a force sensing insertion tool. Furthermore, recent studies have shown significant variability in manual insertion forces and velocities that may explain some instances of imperfect placement. Toward addressing this, an automated insertion tool was recently developed by Hussong et al. By following the same insertion tool concept, in this paper, we present mechanical enhancements that improve the surgeons interface with the device and make it smaller and lighter. We also present electomechanical design of new components enabling integrated force sensing. The tool is designed to be sufficiently compact and light that it can be mounted to a microstereotactic frame for accurate image-guided preinsertion positioning. The new integrated force sensing system is capable of resolving forces as small as 0.005 N, and we provide experimental illustration of using forces to detect errors in electrode insertion.

Automated insertion of preformed cochlear implant electrodes: evaluation of curling behaviour and insertion forces on an artificial cochlear model

PurposeAs a substantial part of our concept of a minimally invasive cochlear implant (CI) surgery, we developed an automated insertion tool. Studies on an artificial scala tympani model were performed in order to evaluate force application when using the insertion tool.MethodsContour electrodes were automatically inserted into a transparent cochlea model in Advance Off-Stylet technique. Occurring forces were measured by the use of a load cell and correlated with observed intracochlear movement of the electrode carriers.ResultsMean insertion forces were measured up to 20 mN comparable to previous studies on temporal bones. The most influencing factor is the implant’s 2D curling behaviour in comparison to the 3D helical shape of the cochlea.ConclusionThe study confirms the functionality and reliability of the automated insertion tool for insertion of preformed CI. Improved insertion strategies considering patient-specific anatomy become possible.

Conception and design of an automated insertion tool for cochlear implants

Cochlear implants (CI) are electronic devices incorporating an electrode inserted into the human cochlea for direct electric stimulation of the auditory nerve. The implantation has become the standard treatment for patients with severe-to-profound sensorineural loss not aidable with conventional hearing aids. The state of the art operative technique is a facial recess approach to the middle ear, following the opening of the scala tympani (cochleostomy) and insertion of the electrode array. The facial recess approach is applicable only by experienced surgeons and optimal CI results primarily depend on optimal electrode placement and minimal traumatic insertion. This also requires a certain amount of experience. Additionally several groups work on minimally-invasive approaches to the cochlea, resulting in the necessity to insert the implant via a keyhole access, which is not applicable with current techniques. This paper presents a mechatronic device for an automated insertion of the electrode array of a cochlear implant system. Being designed especially for minimally-invasive approaches, the tool is also applicable for regular facial recess approaches. Moreover the device allows reliable and repeatable insertion studies at synthetic models or cadaver specimen. The functionality of the tool is proofed with first experiments on a synthetic model.

A force sensing Automated Insertion Tool for cochlear electrode implantation

Cochlear electrode insertion is a challenging manual procedure. One technique requires the physician to coordinate the motions of an electrode array approximately 1mm in diameter and the smaller stylet within it, using miniature forceps. A new minimally invasive access technique precludes forceps insertion because the electrode must travel through a small-diameter drilled hole to reach the cochlear access point. To address this, we present an automated insertion tool. This second generation device not only enables deployment in the minimally invasive setting, but also makes insertion velocity profiles repeatable and can sense insertion forces. Force sensing is essential because insertion forces can indicate impending damage to cochlear membranes, but are below the thresholds that can be sensed by human hands. The Automated Insertion Tool we present is designed to be compact and lightweight for straightforward integration into the operating room environment. It is able to insert an electrode with a resolution of less than 1µm, achieve velocities of up to 5mm/sec and resolve forces as small as 0.005 N.

Temporal bone borehole accuracy for cochlear implantation influenced by drilling strategy: an in vitro study

PurposeMinimally invasive cochlear implantation is a surgical technique which requires drilling a canal from the mastoid surface toward the basal turn of the cochlea. The choice of an appropriate drilling strategy is hypothesized to have significant influence on the achievable targeting accuracy. Therefore, a method is presented to analyze the contribution of the drilling process and drilling tool to the targeting error isolated from other error sources.MethodsThe experimental setup to evaluate the borehole accuracy comprises a drill handpiece attached to a linear slide as well as a highly accurate coordinate measuring machine (CMM). Based on the specific requirements of the minimally invasive cochlear access, three drilling strategies, mainly characterized by different drill tools, are derived. The strategies are evaluated by drilling into synthetic temporal bone substitutes containing air-filled cavities to simulate mastoid cells. Deviations from the desired drill trajectories are determined based on measurements using the CMM.ResultsUsing the experimental setup, a total of 144 holes were drilled for accuracy evaluation. Errors resulting from the drilling process depend on the specific geometry of the tool as well as the angle at which the drill contacts the bone surface. Furthermore, there is a risk of the drill bit deflecting due to synthetic mastoid cells.ConclusionsA single-flute gun drill combined with a pilot drill of the same diameter provided the best results for simulated minimally invasive cochlear implantation, based on an experimental method that may be used for testing further drilling process improvements.

An automated insertion tool for cochlear implants with integrated force sensing capability

Purpose Minimally invasive cochlear implantation and residual hearing preservation require both the surgical approach to the cochlea as well as the implant insertion to be performed in an atraumatic fashion. Considering the geometric limitations of this approach, specialized instrumentation is required to insert the electrode while preserving intracochlear membranes carrying the sensory hair cells.Methods An automated insertion tool for cochlear implants, which is capable of sensing insertion forces with a theoretical resolution of