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OBJECTIVE: Surgeons have no direct objective feedback on cochlear-implant electrode array (EA) positioning during insertion, yet optimal hearing outcomes are contingent on placing the EA as close as feasible to viable neural endings. This paper describes a system to non-invasively determine intracochlear positioning of an EA, without requiring any modifications to existing commercial EAs themselves. METHODS: Electrical impedance has been suggested as a way to measure EA proximity to the inner wall of the cochlea that houses auditory nerve endings—the modiolus. In this paper, we extend prior work and demonstrate for the first time the relationship between bipolar access resistance and proximity of the EA to the modiolus (E-M proximity). We also evaluate two methods for producing direct, real-time estimates of E-M proximity from bipolar impedance measurements. RESULTS: We show that bipolar access resistance is highly correlated with E-M proximity and can be approximately modeled by a power law function. This one dimensional model is shown to be capable of producing accurate real-time estimates of E-M proximity, but its simplicity also limits the potential for future improvement. To address this challenge, we propose a new prediction approach based on a recurrent neural network, which generated an overall prediction accuracy of 93.7%. CONCLUSION: Bipolar access resistance is highly correlated with E-M proximity, and can be used to estimate EA positioning. SIGNIFICANCE: This work shows how impedance sensing can be used to localize an EA during insertion into the small, enclosed cochlear environment, without requiring any modifications to existing clinically used EAs.

Cochlear-implant electrode arrays (EAs) must be inserted accurately and precisely to avoid damaging the delicate anatomical structures of the inner ear. It has previously been shown on the benchtop that using magnetic fields to steer magnet-tipped EAs during insertion reduces insertion forces, which correlate with insertion errors and damage to internal cochlear structures. This letter presents several advancements toward the goal of deploying magnetic steering of cochlear-implant EAs in the operating room. In particular, we integrate image guidance with patient-specific insertion vectors, we incorporate a new nonmagnetic insertion tool, and we use an electromagnetic source, which provides programmable control over the generated field. The electromagnet is safer than prior permanent-magnet approaches in two ways: it eliminates motion of the field source relative to the patient's head and creates a field-free source in the power-off state. Using this system, we demonstrate system feasibility by magnetically steering EAs into a cadaver cochlea for the first time. We show that magnetic steering decreases average insertion forces, in comparison to manual insertions and to image-guided robotic insertions alone.

HYPOTHESIS Undesirable forces applied to the basilar membrane during surgical insertion of lateral-wall cochlear-implant electrode arrays (EAs) can be reduced via robotic insertion with magnetic steering of the EA tip. BACKGROUND Robotic insertion of magnetically steered lateral-wall EAs has been shown to reduce insertion forces in vitro and in cadavers. No previous study of robot-assisted insertion has considered force on the basilar membrane. METHODS Insertions were executed in an open-channel scala-tympani phantom. A force plate, representing the basilar membrane, covered the channel to measure forces in the direction of the basilar membrane. An electromagnetic source generated a magnetic field to steer investigational EAs with permanent magnets at their tips, while a robot performed the insertion. RESULTS When magnetic steering was sufficient to pull the tip of the EA off of the lateral wall of the channel, it resulted in at least a 62% reduction of force on the phantom basilar membrane at insertion depths beyond 14.4 mm (p

Objective Minimally invasive, image-guided cochlear implantation (CI) surgery consists of drilling a precise tunnel from the surface of the mastoid cortex through the facial recess to target the scala tympani. In the first set of clinical trials of this technique, heat-induced facial nerve paresis (House-Brackmann II/VI) occurred on a patient on the last day of the initial trial which was scheduled to be halted secondary to a change in the regulatory requirements dictated by the 2012 the Food and Drug Administration Safety and Innovation Act requiring Investigational Device Exemption approval for previously exempted customized medical device testing. To address this adverse event, extensive changes were made to the drilling protocol; additionally, a custom insertion tool was developed. To address the Food and Drug Administration Safety and Innovation Act, an Investigational Device Exemption was submitted and, subsequently approved. Herein is described our first clinical implementation of the modified technique. Patient Seventy-year-old with profound, postlingual sensorineural hearing loss who had previously undergone right CI via traditional approach in 2015. Intervention Minimally invasive image-guided left CI. Main outcome measure Time of intervention, final location of CI electrode array within cochlea. Results Surgery took 155 minutes of which the largest components (in descending order) were soft tissue work, closure, and drilling. Full scala tympani insertion with angular insertion depth of 557 degrees of the electrode array was achieved. There were no complications, and the patient had an uneventful recovery and activation. Conclusions Minimally invasive, image-guided CI surgery is achievable and reduces the mastoid depression associated with traditional CI surgery. Clinicaltrialsgov information Study NCT03101917, Microtable Microstereotactic Frame and Drill Press and Associated Method for Cochlear Implantation. Level of evidence Case Report.

Image-guided, minimally-invasive cochlear implant surgery is a novel “keyhole” surgical approach for placing a cochlear implant electrode array eliminating the need for a wide-field mastoidectomy approach. Image guidance is used for path planning which is followed by the construction of a customized micro-stereotactic frame to drill a narrow channel from the skull surface to the cochlea. Herein, we present an insertion tool that uses roller wheels to advance the electrode array through the narrow tunnel and into the cochlea. Testing in a phantom revealed that when compared to insertions with surgical forceps, the new insertion tool was on average 26s faster, produced complete insertions more often (i.e. in 6/6 trials, vs. 1/6), and reduced array buckling (0/6 trials vs. 5/6). The tool provides a viable solution to complete the last step of this novel, minimally-invasive procedure. It also provides the advantage over previously developed manual insertion tools of enabling the surgeon to blindly actuate the roller wheel tool to advance the electrode into the tunnel. This allows the surgeon to visualize and guide insertion into the cochlea from a more advantageous visual perspective.

Cochlear implant surgery typically requires a wide-field mastoidectomy to access the cochlea. This portion of the surgery can leave a visible and palpable depression behind the patient's ear, which can be cosmetically displeasing to the patient. For the surgeon, a wide-field mastoidectomy is challenging to perform because bone must be gradually removed by freehand drilling guided primarily by visual feedback in an effort to detect, yet avoid, vital anatomy including the facial nerve which controls motion of the face. Toward overcoming these issues and standardizing surgery, imaged-guided, minimally invasive approaches have been developed in which the cochlea is accessed using a single pre-planned drill trajectory. This approach promises decreased invasiveness, but the limited surgical view and long narrow opening to the cochlea present significant challenges for inserting electrode arrays. This paper describes the first cadaver experiments using a new manual insertion tool which provides a roller mechanism to enable the physician to deploy a cochlear implant electrode array through the narrow drilled hole created by this minimally invasive, image-guided access technique. Results demonstrate that the new tool enables consistent and successful insertions similar to insertions with the traditional tool while increasing the ease of the insertion and freeing the surgeon to monitor progress and make fine adjustments as needed.

Cochlear implants must be inserted carefully to avoid damaging the delicate anatomical structures of the inner ear. This has motivated several approaches to improve the safety and efficacy of electrode array insertion by automating the process with specialized robotic or manual insertion tools. When such tools are used, they must be positioned at the entry point to the cochlea and aligned with the desired entry vector. This paper presents an image guidance system capable of accurately positioning a cochlear implant insertion tool. An optical tracking system localizes the insertion tool in physical space while a graphical user interface incorporates this with patient- specific anatomical data to provide error information to the surgeon in real-time. Guided by this interface, novice users successfully aligned the tool with an mean accuracy of 0.31 mm.