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

A sensory-guided surgical micro-drill

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2010 The Authors.This article describes a surgical robotic device that is able to discriminate tissue interfaces and other controlling parameters ahead of the drill tip. The advantage in such a surgery is that the tissues at the interfaces can be preserved. A smart tool detects ahead of the tool point and is able to control the interaction with respect to the flexing tissue, to avoid penetration or to control the extent of protrusion with respect to the position of the tissue. For surgical procedures, where precision is required, the tool offers significant benefit. To interpret the drilling conditions and the conditions leading up to breakthrough at a tissue interface, a sensing scheme is used that discriminates between the variety of conditions posed in the drilling environment. The result is a fully autonomous system, which is able to respond to the tissue type, behaviour, and deflection in real-time. The system is also robust in terms of disturbances encountered in the operating theatre. The device is pragmatic. It is intuitive to use, efficient to set up, and uses standard drill bits. The micro-drill, which has been used to prepare cochleostomies in the theatre, was used to remove the bone tissue leaving the endosteal membrane intact. This has enabled the preservation of sterility and the drilling debris to be removed prior to the insertion of the electrode. It is expected that this technique will promote the preservation of hearing and reduce the possibility of complications. The article describes the device (including simulated drill progress and hardware set-up) and the stages leading up to its use in the theatre.Queen Elizabeth Hospital, Birmingham, U

Feasibility study of a hand guided robotic drill for cochleostomy

The concept of a hand guided robotic drill has been inspired by an automated, arm supported robotic drill recently applied in clinical practice to produce cochleostomies without penetrating the endosteum ready for inserting cochlear electrodes. The smart tactile sensing scheme within the drill enables precise control of the state of interaction between tissues and tools in real-time. This paper reports development studies of the hand guided robotic drill where the same consistent outcomes, augmentation of surgeon control and skill, and similar reduction of induced disturbances on the hearing organ are achieved. The device operates with differing presentation of tissues resulting from variation in anatomy and demonstrates the ability to control or avoid penetration of tissue layers as required and to respond to intended rather than involuntary motion of the surgeon operator. The advantage of hand guided over an arm supported system is that it offers flexibility in adjusting the drilling trajectory. This can be important to initiate cutting on a hard convex tissue surface without slipping and then to proceed on the desired trajectory after cutting has commenced. The results for trials on phantoms show that drill unit compliance is an important factor in the design

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

Doctor of Philosophy

dissertationFor many with severe-to-profound hearing loss, a condition in which the cochlea is unable to convert sound vibration into neural information to the brain, the cochlear implant has become the standard treatment. The goal of a cochlear-implant system is to bypass the malfunctioned cochlea and directly stimulate the nerves responsible for hearing through an array of electrodes on a silicone-elastomer carrier. However, the insertion of the electrode arrays can often cause intracochlear damage and eliminate residual hearing. With increased focus on hearing preservation in cochlear implantation, methods to minimize intracochlear damage have become a priority in electrode-array insertions. This dissertation explores the application of magnetic manipulation toward improved cochlear-implant electrode-array insertions. We start with initial 3-to-1 proof-of-concept experiments to demonstrate the feasibility of this approach. Then, to achieve relevancy at clinical scale, lateral-wall-type electrode-array models, used in the clinic, are slightly modified at the tip to include a tiny magnet. Next, a scala-tympani phantom is designed with both simulated cochleostomy and round-window openings to mimic both classes of insertions typically conducted. In particular, this is the first phantom to model a round-window opening and can be used reliably to simulate insertion forces in cadaver cochleae. Electrode arrays are then magnetically guided through these phantoms with a statistically significant (p < 0.05) reduction in insertion forces, and by as much as 50% for some electrode-array models. In particular, guiding the electrode-array tip through the cochlear hook and the basal turn, in the same insertion, was demonstrated for the first time using this technology. All existing methods to guide the electrode array can only be accomplished for the basal turn. Analysis is conducted to determine the optimal size and placement of a magnetic dipole-field source for use in the clinic. Its placement is determined to be consistently lateral to and anterior to the patient’s cochlea. Its size depends on numerous factors including the patient, torque requirements, and registration error. Sensitivity curves summarizing these factors are provided. The volume of the magnetic dipole-field source can be reduced by a factor of 5, on average, by moving it from the modiolar configuration originally proposed to this optimal configuration. We verify that magnetic forces do not pose any appreciable risk to the basilar membrane at the optimal configuration. Although patient-specific optimal configurations are characterized, a one-size-fits-all version is described that may be more practical and carries the benefit of substantial robustness to registration error

In-Vitro Study of Speed and Alignment Angle in Cochlear Implant Electrode Array Insertions

Objective: The insertion of the electrode array is a critical step in cochlear implantation. Herein we comprehensively investigate the impact of the alignment angle and feed-forward speed on deep insertions in artificial scala tympani models with accurate macro-anatomy and controlled frictional properties. Methods: Motorized insertions (n=1033) were performed in six scala tympani models with varying speeds and alignment angles. We evaluated reaction forces and micrographs of the insertion process and developed a mathematical model to estimate the normal force distribution along the electrode arrays. Results: Insertions parallel to the cochlear base significantly reduce insertion energies and lead to smoother array movement. Non-constant insertion speeds allow to reduce insertion forces for a fixed total insertion time compared to a constant feed rate. Conclusion: In cochlear implantation, smoothness and peak forces can be reduced with alignment angles parallel to the scala tympani centerline and with non-constant feed-forward speed profiles. Significance: Our results may help to provide clinical guidelines and improve surgical tools for manual and automated cochlear implantation

The feasibility of a novel sensing system for robotic cochlear electrode array feed for hearing preservation

A cochlear implant (CI) was a small electronic device that could provide direct electrical stimulation to the auditory nerve. Unlike a hearing aid, a cochlear implant turned sounds into electrical pulses which were sent directly to the auditory nerve. During a cochlear implant surgery, intracochlear electrode array insertion was considered to be a crucial process. However, the behaviour of the intracochlear electrode array during the insertion remained unclear to surgeons and the behaviour was hardly diagnosed by normal methods. In order to minimize or eliminate the trauma induced by electrode array insertion, we proposed an electrode capacitive sensing method to discriminate among certain signal patterns and notify the surgeons whether the array was placed correctly during the insertion process. In this thesis, we firstly investigated the mechanical behaviour of a CI electrode array during the insertion process. A force model simulating the first contact between the array tip and cochlear inner wall was proposed. Experimental results demonstrated that insertion force was not an effective method for detecting the array behaviours inside of the cochlea. Secondly, we investigated the theory and influencing factors of the capacitive sensing measurements. The relationship between capacitance measured and environmental effect, structural effect and applied force were examined and assessed. Our exploration demonstrated that the measured bipolar capacitive signals were recognised to be sensitive, consistent and reliable. Experiment results revealed that electrode capacitance values were systematically affected by intracochlear forces between the scala tympani wall and the contact electrode. Thirdly, by analysing the bipolar capacitance experimental results, three CI electrode array insertion patterns between the array and the cochlear lateral wall were classified. The possibility of the three patterns which an unknown insertion would fall into could be discriminated by the Principal Component Analysis (PCA) and The Pearson Correlation Coefficient (PCC) analysis. Experiment results showed the overall identification success rate was over 80%. Finally, a multi-channel switch board was proposed to measure multiple electrode pairs at the same time during the array insertion. Measurements and verification based on the board were carried out and shown to be efficient for capacitive signals measuring and recording

Flexible tactile digital feedback for clinical applications

Trauma and damage to the delicate structures of the inner ear frequently occurs during insertion of electrode array into the cochlea. This is strongly related to the excessive manual insertion force of the surgeon without any tool/tissue interaction feedback. The research is examined tool-tissue interaction of large prototype scale (12.5:1) digit embedded with distributive tactile sensor based upon cochlear electrode and large prototype scale (4.5:1) cochlea phantom for simulating the human cochlear which could lead to small scale digit requirements. This flexible digit classified the tactile information from the digit-phantom interaction such as contact status, tip penetration, obstacles, relative shape and location, contact orientation and multiple contacts. The digit, distributive tactile sensors embedded with silicon-substrate is inserted into the cochlea phantom to measure any digit/phantom interaction and position of the digit in order to minimize tissue and trauma damage during the electrode cochlear insertion. The digit is pre-curved in cochlea shape so that the digit better conforms to the shape of the scala tympani to lightly hug the modiolar wall of a scala. The digit have provided information on the characteristics of touch, digit-phantom interaction during the digit insertion. The tests demonstrated that even devices of such a relative simple design with low cost have potential to improve cochlear implants surgery and other lumen mapping applications by providing tactile feedback information by controlling the insertion through sensing and control of the tip of the implant during the insertion. In that approach, the surgeon could minimize the tissue damage and potential damage to the delicate structures within the cochlear caused by current manual electrode insertion of the cochlear implantation. This approach also can be applied diagnosis and path navigation procedures. The digit is a large scale stage and could be miniaturized in future to include more realistic surgical procedures

An investigation of cochlear dynamics in surgical and implanation processes

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The aim of this research is to improve the understanding of the impact on the cochlear dynamics corresponding to surgical tools, processes and hearing implants such that these can be designed more appropriately in the future. The results suggest that enhanced performance of implants can be achieved by optimisation of the location with respect to the cochlea and have shown that robotic surgical tools used to enable precise, simplified processes can reduce harm and offer other benefits. With an ageing population, and where exposure to noise on daily basis is increased rather than industrial settings, at least two factors of age and noise, will contribute to a greater incidence of hearing loss in the population in the future. In the research a mathematical model of the passive cochlea was produced to increase understanding of the sensitivity and behaviour of the fluid, structure and pressure transients within the cochlea. The investigation has been complemented by an innovative experimental technique developed to evaluate the dynamics in the cochlear fluids while maintaining the integrity of the cochlear structure. This technique builds on the success of the state-of-the-art surgical robotic micro-drill. The micro-drill enables removal of bone tissue to prepare a consistent aperture onto the endosteal membrane within the cochlea. This is known as preparing a ‘Third window’. In this technique the motion of the exposed endosteal membrane is treated as the diaphragm element of a pressure transducer and is measured using a Micro- Scanning Laser Vibrometer operating through a microscope. There are two principal outcomes of the research: First, the approach has enabled disturbances in the cochlea to be contrasted for different surgical techniques, which it is expected to allude preferential methods in future surgery in otology. In particular it was shown that when using the robotic micro-drill to create a cochleostomy that the disturbance amplitude reduces to 1% of that experienced when using conventional drilling. Secondly, an empirically derived frequency map of the cochlea has been produced to understand how the location of implants affects maximum power transmission over the required frequency band. This has also shown the feasibility of exciting the cochlea at a third window in order to amplify cochlear response

Real-Time Data-Driven Approach for Prediction and Correction of Electrode Array Trajectory in Cochlear Implantation

Cochlear implants provide hearing perception to people with severe to profound hearing loss. The electrode array (EA) inserted during the surgery directly stimulates the hearing nerve, bypassing the acoustic hearing system. The complications during the EA insertion in the inner ear may cause trauma leading to infection, residual hearing loss, and poor speech perception. This work aims to reduce the trauma induced during electrode array insertion process by carefully designing a sensing method, an actuation system, and data-driven control strategy to guide electrode array in scala tympani. Due to limited intra-operative feedback during the insertion process, complex bipolar electrical impedance is used as a sensing element to guide EA in real time. An automated actuation system with three degrees of freedom was used along with a complex impedance meter to record impedance of consecutive electrodes. Prediction of EA direction (medial, middle, and lateral) was carried out by an ensemble of random forest, shallow neural network, and k-nearest neighbour in an offline setting with an accuracy of 86.86%. The trained ensemble was then utilized in vitro for prediction and correction of EA direction in real time in the straight path with an accuracy of 80%. Such a real-time system also has application in other electrode implants and needle and catheter insertion guidance.Royal National Institute for Deaf people (RNID), formerly known as AoH