Daniel Schurzig

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°).

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.

Force of cochlear implant electrode insertion performed by a robotic insertion tool: comparison of traditional versus Advance Off-Stylet techniques

Objective: Robotic cochlear implant electrode array insertion offers substantial potential advantages, namely repeatability and minimization of insertion forces, leading to decreased intracochlear trauma. Using such a robotic insertion tool, we sought to analyze force profiles during deployment of stylet-containing electrode arrays using either traditional insertion, in which the stylet is withdrawn after complete insertion of the electrode, or Advance Off-Stylet (AOS) insertion, in which the stylet is withdrawn simultaneous with electrode array insertion. Study Design: Prospective. Setting: Tertiary referral center. Interventions: A robotic cochlear implant insertion tool coupled with a force-sensing carriage was used to perform electrode array insertions into an anatomically correct, three-dimensional scala tympani model during either straight insertion (n = 4) or AOS insertion (n = 4). Main Outcome Measures: Both insertion techniques begin with a 7-mm straight insertion during which forces were similar averaging approximately 0.006 N. For insertion from 7 to 17 mm, traditional insertion forces averaged 0.046 ± 0.027 N, with a peak of 0.093 N, and AOS insertion forces averaged 0.008 ± 0.006 N, with a peak of 0.034 N. Beyond 9.74 mm, the difference between traditional and AOS insertion forces was highly significant. Conclusion: With the use of a robotic insertion tool, which minimizes operator variability and maximizes repeatability, we have shown that cochlear implant electrode insertion via AOS is associated with lower average and maximum insertion forces compared with traditional insertion. These findings support the use of AOS over traditional, straight insertion.

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.

Evaluation of portable CT scanners for otologic image-guided surgery

PurposePortable CT scanners are beneficial for diagnosis in the intensive care unit, emergency room, and operating room. Portable fixed-base versus translating-base CT systems were evaluated for otologic image-guided surgical (IGS) applications based on geometric accuracy and utility for percutaneous cochlear implantation.MethodsFive cadaveric skulls were fitted with fiducial markers and scanned using both a translating-base, 8-slice CT scanner (CereTom®) and a fixed-base, flat-panel, volume CT (fpVCT) scanner (Xoran xCAT®). Images were analyzed for: (a) subjective quality (i.e., noise), (b) consistency of attenuation measurements (Hounsfield units) across similar tissue, and (c) geometric accuracy of fiducial marker positions. The utility of these scanners in clinical IGS cases was tested.ResultsFive cadaveric specimens were scanned using each of the scanners. The translating-base, 8-slice CT scanner had spatially consistent Hounsfield units, and the image quality was subjectively good. However, because of movement variations during scanning, the geometric accuracy of fiducial marker positions was low. The fixed-base, fpVCT system had high spatial resolution, but the images were noisy and had spatially inconsistent attenuation measurements, while the geometric representation of the fiducial markers was highly accurate.ConclusionTwo types of portable CT scanners were evaluated for otologic IGS. The translating-base, 8-slice CT scanner provided better image quality than a fixed-base, fpVCT scanner. However, the inherent error in three-dimensional spatial relationships by the translating-based system makes it suboptimal for otologic IGS use.

A Manually Operated, Advance Off-Stylet Insertion Tool for Minimally Invasive Cochlear Implantation Surgery

The current technique for cochlear implantation (CI) surgery requires a mastoidectomy to gain access to the cochlea for electrode array insertion. It has been shown that microstereotactic frames can enable an image-guided, minimally invasive approach to CI surgery called percutaneous cochlear implantation (PCI) that uses a single drill hole for electrode array insertion, avoiding a more invasive mastoidectomy. Current clinical methods for electrode array insertion are not compatible with PCI surgery because they require a mastoidectomy to access the cochlea; thus, we have developed a manually operated electrode array insertion tool that can be deployed through a PCI drill hole. The tool can be adjusted using a preoperative CT scan for accurate execution of the advance off-stylet (AOS) insertion technique and requires less skill to operate than is currently required to implant electrode arrays. We performed three cadaver insertion experiments using the AOS technique and determined that all insertions were successful using CT and microdissection.

Insertion of electrode array using percutaneous cochlear implantation technique: a cadaveric study

Cochlear implantation is a surgical procedure for treating patients with hearing loss in which an electrode array is inserted into the cochlea. The traditional surgical approach requires drilling away a large portion of the bone behind the ear to provide anatomical reference and access to the cochlea. A minimally-invasive technique, called percutaneous cochlear implantation (PCI), has been proposed that involves drilling a linear path from the lateral skull to the cochlea avoiding vital structures and inserting the implant using that drilled path. The steps required to achieve PCI safely include: placing three bone-implanted markers surrounding the ear, obtaining a CT scan, planning a surgical path to the cochlea avoiding vital anatomy, designing and constructing a microstereotactic frame that mounts on the markers and constrains the drill to the planned path, affixing the frame on the markers, using it to drill to the cochlea, and inserting the electrode through the drilled path. We present in this paper a cadaveric study demonstrating the PCI technique on three temporal bone cadaveric specimens for inserting electrode array into the cochlea. A custom fixture, called a Microtable, which is a type of microstereotactic frame that can be constructed in less than five minutes, was fabricated for each specimen and used to reach the cochlea. The insertion was successfully performed on all three specimens. Postinsertion CT scans confirm the correct placement of the electrodes inside the cochlea without any damage to the facial nerve.

A MANUAL INSERTION MECHANISM FOR PERCUTANEOUS COCHLEAR IMPLANTATION

Percutaneous cochlear implantation (PCI) is a recently developed minimally invasive technique that utilizes image guidance and a custom-made microstereotactic frame to guide a drill directly to the cochlea. It enables cochlear access through a single drill port, reducing invasiveness in comparison to mastoidectomy. With the reduction in invasiveness, PCI enables a corresponding reduction in visualization and space in which to work at the cochlear entry point. This precludes standard cochlear implant deployment techniques and necessitates a new insertion tool that can deploy a cochlear implant into the cochlea while working down a deep, narrow channel. In this paper, we describe a manual insertion tool that we have developed for this purpose. The tool is capable of inserting an electrode array into the cochlea using the advance off-stylet technique, using simple manual controls on its handle.

Cochlear helix and duct length identification – Evaluation of different curve fitting techniques

Objective: Within the field of cochlear implantation (CIs), the role of utilizing patient-specific cochlear anatomy for choosing the optimal implant electrode is becoming increasingly important. Unfortunately, performing detailed anatomical measurements of a cochlea using clinical imaging data is rather time consuming and hence difficult to implement into the clinical routine. In order to accelerate clinical cochlear anatomy evaluations, previously developed mathematical models can be adjusted to the patient-specific anatomy by measuring just a few overall cochlear dimensions. However, the accuracy of model-based cochlear anatomy estimations is unclear, and incorrect evaluations may lead to false conclusions regarding the suitability of specific implant electrodes. Methods: Based on 10 cochleae, an error evaluation of various commonly used curve fitting approaches for cochlear shape and duct length approximation was conducted. Spline tracings of the cochlear contours were used as reference values for the various approximations. Results: Parameterized average cochlear helix models and two of five analytical approaches were found to be suitable for reconstructing the cochlear helical shape and estimating its length. Discussion: Spline curve reconstructions are the most accurate and reliable method for assessing patient-specific cochlear geometry, especially in the case of anatomical irregularities. The most accurate results within the group of model-based evaluations still resulted in mean overall cochlear length deviations of approximately 5%. Conclusion: Spline curve reconstructions appear to be the best option for anatomical diagnostics in clinical practice. Retrospective studies can be performed to further evaluate model-based evaluations.