Automatic segmentation of intracochlear anatomy in conventional CT

Preliminary Results With Image-guided Cochlear Implant Insertion Techniques

HYPOTHESIS

Using patient-customized cochlear measurements obtained from preoperative computed tomography (CT) scans to guide insertion of cochlear implant (CI) electrode arrays will lead to more optimal intracochlear positioning.

BACKGROUND

Cochlear duct length is highly variable ranging from 25.26 to 35.46 mm, yet CI electrode arrays are treated as one size fits most. We sought to investigate the impact of patient-customized insertion plans on final location of electrode arrays.

METHODS

Twenty cadaveric temporal bone specimens were CT scanned and randomly divided into groups A and B. Group A specimens had an optimal customized insertion plan generated including entry site (e.g., round window versus extended round window), entry vector based on anatomical landmarks (e.g., hug posterior aspect of facial recess and angle 1 mm inferior to stapes), depth to begin advancing off stylet, and final insertion depth. Suboptimal plans were chosen for group B by selecting an approach that was normal yet predicted to result in poor final electrode location. One surgeon, blinded as to group, carried out the CI insertions following which the electrode array was fixed using superglue and the specimen CT scanned to allow assessment of final electrode location.

RESULTS

Average perimodiolar distances for groups A and B were 0.51 and 0.60 mm, respectively. For group A, full scala tympani insertion was achieved in all specimens while in group B, 4 of 10 specimens had scalar translocation.

CONCLUSION

Patient customized cochlear implant insertion techniques achieved better positioning of electrode arrays in this study and have potential for improving electrode positioning in patients.

Prevalence of Extracochlear Electrodes: Computerized Tomography Scans, Cochlear Implant Maps, and Operative Reports

OBJECTIVE

To quantify and compare the number of cochlear implant (CI) electrodes found to be extracochlear on postoperative computerized tomography (CT) scans, the number of basal electrodes deactivated during standard CI mapping (without knowledge of the postoperative CT scan), and the extent of electrode insertion noted by the surgeon.

STUDY DESIGN

Retrospective.

SETTING

Academic Medical Center.

METHODS

Two hundred sixty-two patients underwent standard cochlear implantation and postoperative temporal bone CT scanning. Scans were analyzed to determine the number of extracochlear electrodes. Standard CI programming had been completed without knowledge of the extracochlear electrodes identified on the CT. These standard CI maps were reviewed to record the number of deactivated basal electrodes. Lastly, each operative report was reviewed to record the extent of reported electrode insertion.

RESULTS

13.4% (n = 35) of CIs were found to have at least one electrode outside of the cochlea on the CT scan. Review of CI mapping indicated that audiologists had deactivated extracochlear electrodes in 60% (21) of these cases. Review of operative reports revealed that surgeons correctly indicated the number of extracochlear electrodes in 6% (2) of these cases.

CONCLUSIONS

Extracochlear electrodes were correctly identified audiologically in 60% of cases and in surgical reports in 6% of cases; however, it is possible that at least a portion of these cases involved postoperative electrode migration. Given these findings, postoperative CT scans can provide information regarding basal electrode location, which could help improve programming accuracy, associated frequency allocation, and audibility with appropriate deactivation of extracochlear electrodes.

An In-Vitro Insertion-Force Study of Magnetically Guided Lateral-Wall Cochlear-Implant Electrode Arrays

Hypothesis:

Insertion forces can be reduced by magnetically guiding the tip of lateral-wall cochlear-implant electrode arrays during insertion via both cochleostomy and the round window.

Background:

Steerable electrode arrays have the potential to minimize intracochlear trauma by reducing the severity of contact between the electrode-array tip and the cochlear wall. However, steerable electrode arrays typically have increased stiffness associated with the steering mechanism. In addition, steerable electrode arrays are typically designed to curve in the direction of the basal turn, which is not ideal for round-window insertions, as the cochlear hook's curvature is in the opposite direction. Lateral-wall electrode arrays can be modified to include magnets at their tips, augmenting their superior flexibility with a steering mechanism. By applying magnetic torque to the tip, an electrode array can be navigated through the cochlear hook and the basal turn.

Methods:

Automated insertions of candidate electrode arrays are conducted into a scala-tympani phantom with either a cochleostomy or round-window opening. The phantom is mounted on a multi-degree-of-freedom force sensor. An external magnet applies the necessary magnetic bending torque to the magnetic tip of a modified clinical electrode array, coordinated with the insertion, with the goal of directing the tip down the lumen. Steering of the electrode array is verified through a camera.

Results:

Statistical t-test results indicate that magnetic guidance does reduce insertion forces by as much as 50% with certain electrode-array models. Direct tip contact with the medial wall through the cochlear hook and the lateral wall of the basal turn is completely eliminated. The magnetic field required to accomplish these insertions varied from 77 to 225 mT based on the volume of the magnet at the tip of the electrode array. Alteration of the tip to accommodate a tiny magnet is minimal and does not change the insertion characteristic of the electrode array unless the tip shape is altered.

Conclusion:

Magnetic guidance can eliminate direct tip contact with the medial walls through the cochlear hook and the lateral walls of the basal turn. Insertion-force reduction will vary based on the electrode-array model, but is statistically significant for all models tested. Successful steering of lateral-wall electrode arrays is accomplished while maintaining its superior flexibility.

Further Evidence of the Relationship Between Cochlear Implant Electrode Positioning and Hearing Outcomes

BACKGROUND

Postoperative imaging studies by numerous groups have revealed that final cochlear implant (CI) electrode position impacts audiological outcomes with scalar location consistently shown to be a significant factor. Modiolar proximity has been less extensively studied, and findings regarding the effect of insertion depth have been inconsistent.

METHODS

Using previously developed automated algorithms, we determined CI electrode position in an Institutional Review Board-approved database of 220 CI ears. Generalized linear models (GLM) were used to analyze the relationship between audiological outcomes and factors including age, duration of CI use, device type, and electrode position.

RESULTS

For precurved arrays, GLM revealed that scalar position, modiolar proximity, base insertion depth, and sex were significant factors for Consonant-Nucleus-Consonant (CNC) words (R = 0.43, p < 0.001, n = 92 arrays), while scalar position, modiolar proximity, age, and postlingual onset of deafness were significant for Bamford-Kawal-Bench Sentences in Noise (BKB-SIN) (R = 0.51, p < 0.001, n = 85) scores. Other factors were not significant in the final model after controlling for these variables. For straight arrays, we found the insertion depth, postlingual deafness, and length of CI use to be highly significant (R = 0.47, p < 0.001) factors for CNC words (91 arrays), while for BKB-SIN scores the most significant (R = 0.47, p < 0.001) factors were insertion depth, younger age, and postlingual deafness (89 arrays).

CONCLUSION

Our results confirm the significance of electrode positioning in audiological outcomes. The most significant positional predictors of outcome for precurved arrays were full scala tympani (ST) insertion and the modiolar distance, while for the lateral wall arrays the depth of insertion was the most significant factor.

Investigating variability in cochlear implant electrode array alignment and the potential of visualization guidance

Background Internal cochlear anatomy is difficult to discern from external inspection, hindering cochlear implant electrode insertion. Methods A user study characterized the repeatability of standard surgical technique and examined the role of visual inspection and guidance cues in reducing electrode array insertion misalignment. Results Without guidance, a large spread in angles of insertion, up to 30°, was observed, highlighting the need for intraoperative guidance. Visual inspection did not significantly improve overall orientation, suggesting the need for alternate intracochlear visualization methods and/or increased training to effectively improve surgeon understanding of the visualized images. Visual cues and guidance software increased repeatability of surgeon performance, reducing one metric of repeatability to ±2°. Conclusions This study establishes a baseline for surgeon variability in cochlear implant insertion and supports the need and lays the groundwork for future intraoperative guidance techniques.

Response Changes During Insertion of a Cochlear Implant Using Extracochlear Electrocochleography

OBJECTIVES

Electrocochleography is increasingly being utilized as an intraoperative monitor of cochlear function during cochlear implantation (CI). Intracochlear recordings from the advancing electrode can be obtained through the device by on-board capabilities. However, such recordings may not be ideal as a monitor because the recording electrode moves in relation to the neural and hair cell generators producing the responses. The purposes of this study were to compare two extracochlear recording locations in terms of signal strength and feasibility as intraoperative monitoring sites and to characterize changes in cochlear physiology during CI insertion.

DESIGN

In 83 human subjects, responses to 90 dB nHL tone bursts were recorded both at the round window (RW) and then at an extracochlear position-either adjacent to the stapes or on the promontory just superior to the RW. Recording from the fixed, extracochlear position continued during insertion of the CI in 63 cases.

RESULTS

Before CI insertion, responses to low-frequency tones at the RW were roughly 6 dB larger than when recording at either extracochlear site, but the two extracochlear sites did not differ from one another. During CI insertion, response losses from the promontory or adjacent to the stapes stayed within 5 dB in ≈61% (38/63) of cases, presumably indicating atraumatic insertions. Among responses which dropped more than 5 dB at any time during CI insertion, 12 subjects showed no response recovery, while in 13, the drop was followed by partial or complete response recovery by the end of CI insertion. In cases with recovery, the drop in response occurred relatively early (<15 mm insertion) compared to those where there was no recovery. Changes in response phase during the insertion occurred in some cases; these may indicate a change in the distributions of generators contributing to the response.

CONCLUSIONS

Monitoring the electrocochleography during CI insertion from an extracochlear site reveals insertions that are potentially atraumatic, show interaction with cochlear structures followed by response recovery, or show interactions such that response losses persist to the end of recording.

The Effect of Simulated Interaural Frequency Mismatch on Speech Understanding and Spatial Release From Masking

OBJECTIVE

The binaural-hearing system interaurally compares inputs, which underlies the ability to localize sound sources and to better understand speech in complex acoustic environments. Cochlear implants (CIs) are provided in both ears to increase binaural-hearing benefits; however, bilateral CI users continue to struggle with understanding speech in the presence of interfering sounds and do not achieve the same level of spatial release from masking (SRM) as normal-hearing listeners. One reason for diminished SRM in CI users could be that the electrode arrays are inserted at different depths in each ear, which would cause an interaural frequency mismatch. Because interaural frequency mismatch diminishes the salience of interaural differences for relatively simple stimuli, it may also diminish binaural benefits for spectral-temporally complex stimuli like speech. This study evaluated the effect of simulated frequency-to-place mismatch on speech understanding and SRM.

DESIGN

Eleven normal-hearing listeners were tested on a speech understanding task. There was a female target talker who spoke five-word sentences from a closed set of words. There were two interfering male talkers who spoke unrelated sentences. Nonindividualized head-related transfer functions were used to simulate a virtual auditory space. The target was presented from the front (0°), and the interfering speech was either presented from the front (colocated) or from 90° to the right (spatially separated). Stimuli were then processed by an eight-channel vocoder with tonal carriers to simulate aspects of listening through a CI. Frequency-to-place mismatch ("shift") was introduced by increasing the center frequency of the synthesis filters compared with the corresponding analysis filters. Speech understanding was measured for different shifts (0, 3, 4.5, and 6 mm) and target-to-masker ratios (TMRs: +10 to -10 dB). SRM was calculated as the difference in the percentage of correct words for the colocated and separated conditions. Two types of shifts were tested: (1) bilateral shifts that had the same frequency-to-place mismatch in both ears, but no interaural frequency mismatch, and (2) unilateral shifts that produced an interaural frequency mismatch.

RESULTS

For the bilateral shift conditions, speech understanding decreased with increasing shift and with decreasing TMR, for both colocated and separate conditions. There was, however, no interaction between shift and spatial configuration; in other words, SRM was not affected by shift. For the unilateral shift conditions, speech understanding decreased with increasing interaural mismatch and with decreasing TMR for both the colocated and spatially separated conditions. Critically, there was a significant interaction between the amount of shift and spatial configuration; in other words, SRM decreased for increasing interaural mismatch.

CONCLUSIONS

A frequency-to-place mismatch in one or both ears resulted in decreased speech understanding. SRM, however, was only affected in conditions with unilateral shifts and interaural frequency mismatch. Therefore, matching frequency information between the ears provides listeners with larger binaural-hearing benefits, for example, improved speech understanding in the presence of interfering talkers. A clinical procedure to reduce interaural frequency mismatch when programming bilateral CIs may improve benefits in speech segregation that are due to binaural-hearing abilities.

Interaural Time-Difference Discrimination as a Measure of Place of Stimulation for Cochlear-Implant Users With Single-Sided Deafness

Current clinical practice in programming a cochlear implant (CI) for individuals with single-sided deafness (SSD) is to maximize the transmission of speech information via the implant, with the implicit assumption that this will also result in improved spatial-hearing abilities. However, binaural sensitivity is reduced by interaural place-of-stimulation mismatch, a likely occurrence with a standard CI frequency-to-electrode allocation table (FAT). As a step toward reducing interaural mismatch, this study investigated whether a test of interaural-time-difference (ITD) discrimination could be used to estimate the acoustic frequency yielding the best place match for a given CI electrode. ITD-discrimination performance was measured by presenting 300-ms bursts of 100-pulses-per-second electrical pulse trains to a single CI electrode and band-limited pulse trains with variable carrier frequencies to the acoustic ear. Listeners discriminated between two reference intervals (four bursts each with constant ITD) and a moving target interval (four bursts with variable ITD). For 17 out of the 26 electrodes tested across eight listeners, the function describing the relationship between ITD-discrimination performance and carrier frequency had a discernable peak where listeners achieved 70% to 100% performance. On average, this peak occurred 1.15 octaves above the CI manufacturer’s default FAT. ITD discrimination shows promise as a method of estimating the cochlear place of stimulation for a given electrode, thereby providing information to optimize the FAT for SSD-CI listeners.

Automatic graph-based method for localization of cochlear implant electrode arrays in clinical CT with sub-voxel accuracy

Cochlear implants (CIs) are neural prosthetics that provide a sense of sound to people who experience severe to profound hearing loss. Recent studies have demonstrated a correlation between hearing outcomes and intra-cochlear locations of CI electrodes. Our group has been conducting investigations on this correlation and has been developing an image-guided cochlear implant programming (IGCIP) system to program CI devices to improve hearing outcomes. One crucial step that has not been automated in IGCIP is the localization of CI electrodes in clinical CTs. Existing methods for CI electrode localization do not generalize well on large-scale datasets of clinical CTs implanted with different brands of CI arrays. In this paper, we propose a novel method for localizing different brands of CI electrodes in clinical CTs. We firstly generate the candidate electrode positions at sub-voxel resolution in a whole head CT by thresholding an up-sampled feature image and voxel-thinning the result. Then, we use a graph-based path-finding algorithm to find a fixed-length path that consists of a subset of the candidates as the localization result. Validation on a large-scale dataset of clinical CTs shows that our proposed method outperforms the state-of-art CI electrode localization methods and achieves a mean error of 0.12 mm when compared to expert manual localization results. This represents a crucial step in translating IGCIP from the laboratory to large-scale clinical use.

Two-level Training of a 3d U-Net for Accurate Segmentation of the Intra-cochlear Anatomy in Head CTs with Limited Ground Truth Training Data

Cochlear implants (CIs) use electrode arrays that are surgically inserted into the cochlea to treat patients with hearing loss. For CI recipients, sound bypasses the natural transduction mechanism and directly stimulates the neural regions, thus creating a sense of hearing. Post-operatively, CIs need to be programmed. Traditionally, this is done by an audiologist who is blind to the positions of the electrodes relative to the cochlea and only relies on the subjective response of the patient. Multiple programming sessions are usually needed, which can take a frustratingly long time. We have developed an image-guided cochlear implant programming (IGCIP) system to facilitate the process. In IGCIP, we segment the intra-cochlear anatomy and localize the electrode arrays in the patient's head CT image. By utilizing their spatial relationship, we can suggest programming settings that can significantly improve hearing outcomes. To segment the intra-cochlear anatomy, we use an active shape model (ASM)-based method. Though it produces satisfactory results in most cases, sub-optimal segmentation still happens. As an alternative, herein we explore using a deep learning method to perform the segmentation task. Large image sets with accurate ground truth (in our case manual delineation) are typically needed to train a deep learning model for segmentation but such a dataset does not exist for our application. To tackle this problem, we use segmentations generated by the ASM-based method to pre-train the model and fine-tune it on a small image set for which accurate manual delineation is available. Using this method, we achieve better results than the ASM-based method.

Automatic localization of closely spaced cochlear implant electrode arrays in clinical CTs

PURPOSE

Cochlear implants (CIs) are neural prosthetic devices that provide a sense of sound to people who experience profound hearing loss. Recent research has indicated that there is a significant correlation between hearing outcomes and the intracochlear locations of the electrodes. We have developed an image-guided cochlear implant programming (IGCIP) system based on this correlation to assist audiologists with programming CI devices. One crucial step in our IGCIP system is the localization of CI electrodes in postimplantation CTs. Existing methods for this step are either not fully automated or not robust. When the CI electrodes are closely spaced, it is more difficult to identify individual electrodes because there is no intensity contrast between them in a clinical CT. The goal of this work is to automatically segment the closely spaced CI electrode arrays in postimplantation clinical CTs.

METHODS

The proposed method involves firstly identifying a bounding box that contains the cochlea by using a reference CT. Then, the intensity image and the vesselness response of the VOI are used to segment the regions of interest (ROIs) that may contain the electrode arrays. For each ROI, we apply a voxel thinning method to generate the medial axis line. We exhaustively search through all the possible connections of medial axis lines. For each possible connection, we define CI array centerline candidates by selecting two points on the connected medial axis lines as the array endpoints. For each CI array centerline candidate, we use a cost function to evaluate its quality, and the one with the lowest cost is selected as the array centerline. Then, we fit an a priori known geometric model of the array to the centerline to localize the individual electrodes. The method was trained on 28 clinical CTs of CI recipients implanted with three models of closely spaced CI arrays. The localization results are compared with the ground truth localization results manually generated by an expert.

RESULTS

A validation study was conducted on 129 clinical CTs of CI recipients implanted with three models of closely spaced arrays. Ninety-eight percent of the localization results generated by the proposed method had maximum localization errors lower than one voxel diagonal of the CTs. The mean localization error was 0.13 mm, which was close to the rater's consistency error (0.11 mm). The method also outperformed the existing automatic electrode localization methods in our validation study.

CONCLUSION

Our validation study shows that our method can localize closely spaced CI arrays with an accuracy close to what is achievable by an expert on clinical CTs. This represents a crucial step toward automating IGCIP and translating it from the laboratory to the clinical workflow.

Accurate Detection of Inner Ears in Head CTs Using a Deep Volume-to-Volume Regression Network with False Positive Suppression and a Shape-Based Constraint

Cochlear implants (CIs) are neural prosthetics which are used to treat patients with hearing loss. CIs use an array of electrodes which are surgically inserted into the cochlea to stimulate the auditory nerve endings. After surgery, CIs need to be programmed. Studies have shown that the spatial relationship between the intra-cochlear anatomy and electrodes derived from medical images can guide CI programming and lead to significant improvement in hearing outcomes. However, clinical head CT images are usually obtained from scanners of different brands with different protocols. The field of view thus varies greatly and visual inspection is needed to document their content prior to applying algorithms for electrode localization and intra-cochlear anatomy segmentation. In this work, to determine the presence/absence of inner ears and to accurately localize them in head CTs, we use a volume-to-volume convolutional neural network which can be trained end-to-end to map a raw CT volume to probability maps which indicate inner ear positions. We incorporate a false positive suppression strategy in training and apply a shape-based constraint. We achieve a labeling accuracy of 98.59% and a localization error of 2.45 mm. The localization error is significantly smaller than a random forest-based approach that has been proposed recently to perform the same task.

Automatic classification of cochlear implant electrode cavity positioning

Cochlear Implants (CIs) restore hearing using an electrode array that is surgically implanted into the intra-cochlear cavities. Research has indicated that each electrode can lie in one of several cavities and that location is significantly associated with hearing outcomes. However, comprehensive analysis of this phenomenon has not been possible because the cavities are not directly visible in clinical CT images and because existing methods to estimate cavity location are not accurate enough, labor intensive, or their accuracy has not been validated. In this work, a novel graph-based search is presented to automatically identify the cavity in which each electrode is located. We test our approach on CT scans from a set of 34 implanted temporal bone specimens. High resolution μCT scans of the specimens, where cavities are visible, show our method to have 98% cavity classification accuracy. These results indicate that our methods could be used on a large scale to study the link between electrode placement and outcome, which could lead to advances that improve hearing outcomes for CI users.

Conditional Generative Adversarial Networks for Metal Artifact Reduction in CT Images of the Ear

We propose an approach based on a conditional generative adversarial network (cGAN) for the reduction of metal artifacts (RMA) in computed tomography (CT) ear images of cochlear implants (CIs) recipients. Our training set contains paired pre-implantation and post-implantation CTs of 90 ears. At the training phase, the cGAN learns a mapping from the artifact-affected CTs to the artifact-free CTs. At the inference phase, given new metal-artifact-affected CTs, the cGAN produces CTs in which the artifacts are removed. As a pre-processing step, we also propose a band-wise normalization method, which splits a CT image into three channels according to the intensity value of each voxel and we show that this method improves the performance of the cGAN. We test our cGAN on post-implantation CTs of 74 ears and the quality of the artifact-corrected images is evaluated quantitatively by comparing the segmentations of intra-cochlear anatomical structures, which are obtained with a previously published method, in the real pre-implantation and the artifact-corrected CTs. We show that the proposed method leads to an average surface error of 0.18 mm which is about half of what could be achieved with a previously proposed technique.

Validation of automatic cochlear implant electrode localization techniques using μ CTs

Cochlear implants (CIs) are standard treatment for patients who experience sensorineural hearing loss. Although these devices have been remarkably successful at restoring hearing, it is rare that they permit to achieve natural fidelity and many patients experience poor outcomes. Our group has developed image-guided CI programming techniques (IGCIP), in which image analysis techniques are used to locate the intracochlear position of CI electrodes to determine patient-customized settings for the CI processor. Clinical studies have shown that IGCIP leads to significantly improved outcomes. A crucial step is the localization of the electrodes, and rigorously quantifying the accuracy of our algorithms requires dedicated datasets. We discuss the creation of a ground truth dataset for electrode position and its use to evaluate the accuracy of our electrode localization techniques. Our final ground truth dataset includes 30 temporal bone specimens that were each implanted with one of four different types of electrode array by an experienced CI surgeon. The arrays were localized in conventional CT images using our automatic methods and manually in high-resolution μ CT images to create the ground truth. The conventional and μ CT images were registered to facilitate comparison between automatic and ground truth electrode localization results. Our technique resulted in mean errors of 0.13 mm in localizing the electrodes across 30 cases. Our approach successfully permitted characterizing the accuracy of our methods, which is critical to understand their limitations for use in IGCIP.

Cochlear implants: Insertion assessment by computed tomography

BACKGROUND AND OBJECTIVES

Imaging exams play a key role in cochlear implants with regard to both planning implantation before surgery and quality control after surgery. The ability to visualize the three-dimensional location of implanted electrodes is useful in clinical routines for assessing patient outcome. The aim of this study was to evaluate linear and angular insertion depth measurements of cochlear implants based on conventional computed tomography.

METHODS

Tools for linear and angular measurements of cochlear implants were used in computed tomography exams. The tools realized the insertion measurements in an image reconstruction of the CIs, based on image processing techniques. We comprehensively characterized two cochlear implant models while obviating possible changes that can be caused by different cochlea sizes by using the same human temporal bones to evaluate the implant models.

RESULTS

The tools used herein were able to differentiate the insertion measurements between two cochlear implant models widely used in clinical practice. We observed significant differences between both insertion measurements because of their different design and construction characteristics (p = 0.004 and 0.003 for linear and angular measurements, respectively; t-test). The presented methodology showed to be a good tool to calculate insertion depth measurements, since it is easy to perform, produces high-resolution images, and is able to depict all the landmarks, thus enabling measurement of the angular and linear insertion depth of the most apical electrode contacts.

CONCLUSION

The present study demonstrates practical and useful tools for evaluating cochlear implant electrodes in clinical practice. Further studies should measure preoperative and postoperative benefits in terms of speech recognition and evaluate the preservation of residual hearing in the implanted ear. Such studies can also determine correlations between surgical factors, electrode positions, and performance. In addition to refined surgical techniques, the precise evaluation of cochlear length and correct choice of cochlear implant characteristics can play an important role in postoperative outcomes.

Automatic Detection of the Inner Ears in Head CT Images Using Deep Convolutional Neural Networks

Cochlear implants (CIs) use electrode arrays that are surgically inserted into the cochlea to stimulate nerve endings to replace the natural electro-mechanical transduction mechanism and restore hearing for patients with profound hearing loss. Post-operatively, the CI needs to be programmed. Traditionally, this is done by an audiologist who is blind to the positions of the electrodes relative to the cochlea and relies on the patient's subjective response to stimuli. This is a trial-and-error process that can be frustratingly long (dozens of programming sessions are not unusual). To assist audiologists, we have proposed what we call IGCIP for image-guided cochlear implant programming. In IGCIP, we use image processing algorithms to segment the intra-cochlear anatomy in pre-operative CT images and to localize the electrode arrays in post-operative CTs. We have shown that programming strategies informed by image-derived information significantly improve hearing outcomes for both adults and pediatric populations. We are now aiming at deploying these techniques clinically, which requires full automation. One challenge we face is the lack of standard image acquisition protocols. The content of the image volumes we need to process thus varies greatly and visual inspection and labelling is currently required to initialize processing pipelines. In this work we propose a deep learning-based approach to automatically detect if a head CT volume contains two ears, one ear, or no ear. Our approach has been tested on a data set that contains over 2,000 CT volumes from 153 patients and we achieve an overall 95.97% classification accuracy.

Optimizing the Magnetic Dipole-Field Source for Magnetically Guided Cochlear-Implant Electrode-Array Insertions

Magnetic guidance of cochlear-implant electrode arrays during insertion has been demonstrated in vitro to reduce insertion forces, which is believed to be correlated to a reduction in trauma. In those prior studies, the magnetic dipole-field source (MDS) was configured to travel on a path that would be coincident with the cochlea's modiolar axis, which was an unnecessary constraint that was useful to demonstrate feasibility. In this paper, we determine the optimal configuration (size and location) of a spherical-permanent-magnet MDS needed to accomplish guided insertions with a 100 mT field strength required at the cochlea, and we provide a methodology to perform such an optimization more generally. Based on computed-tomography scans of 30 human subjects, the MDS should be lateral-to and slightly anterior-to the cochlea with an approximate radius (mean and standard deviation across subjects) of 64 mm and 4.5 mm, respectively. We compare these results to the modiolar configuration and find that the volume of the MDS can be reduced by a factor of five with a 43% reduction in its radius by moving it to the optimal location. We conservatively estimate that the magnetic forces generated by the optimal configuration are two orders of magnitude below the threshold needed to puncture the basilar membrane. Although subject-specific optimal configurations are computed in this paper, a one-size-fits-all version with a radius of approximately 75 mm is more robust to registration error and likely more practical. Finally, we explain how to translate the results obtained to an electromagnetic MDS.

Co-registration of cone beam CT and preoperative MRI for improved accuracy of electrode localization following cochlear implantation

OBJECTIVES

To investigate the clinical usefulness and practicality of co-registration of Cone Beam CT (CBCT) with preoperative Magnetic Resonance Imaging (MRI) for intracochlear localization of electrodes after cochlear implantation.

METHODS

Images of 20 adult patients who underwent CBCT after implantation were co-registered with preoperative MRI scans. Time taken for co-registration was recorded. The images were analysed by clinicians of varying levels of expertise to determine electrode position and ease of interpretation.

RESULTS

After a short learning curve, the average co-registration time was 10.78 minutes (StdDev 2.37). All clinicians found the co-registered images easier to interpret than CBCT alone. The mean concordance of CBCT vs. co-registered image analysis between consultant otologists was 60% (17-100%) and 86% (60-100%), respectively. The sensitivity and specificity for CBCT to identify Scala Vestibuli insertion or translocation was 100 and 75%, respectively. The negative predictive value was 100%.

DISCUSSION

CBCT should be performed following adult cochlear implantation for audit and quality control of surgical technique. If SV insertion or translocation is suspected, co-registration with preoperative MRI should be performed to enable easier analysis. There will be a learning curve for this process in terms of both the co-registration and the interpretation of images by clinicians.

Patient-specific estimation of detailed cochlear shape from clinical CT images

PURPOSE

A personalized estimation of the cochlear shape can be used to create computational anatomical models to aid cochlear implant (CI) surgery and CI audio processor programming ultimately resulting in improved hearing restoration. The purpose of this work is to develop and test a method for estimation of the detailed patient-specific cochlear shape from CT images.

METHODS

From a collection of temporal bone [Formula: see text]CT images, we build a cochlear statistical deformation model (SDM), which is a description of how a human cochlea deforms to represent the observed anatomical variability. The model is used for regularization of a non-rigid image registration procedure between a patient CT scan and a [Formula: see text]CT image, allowing us to estimate the detailed patient-specific cochlear shape.

RESULTS

We test the accuracy and precision of the predicted cochlear shape using both [Formula: see text]CT and CT images. The evaluation is based on classic generic metrics, where we achieve competitive accuracy with the state-of-the-art methods for the task. Additionally, we expand the evaluation with a few anatomically specific scores.

CONCLUSIONS

The paper presents the process of building and using the SDM of the cochlea. Compared to current best practice, we demonstrate competitive performance and some useful properties of our method.

Localizing landmark sets in head CTs using random forests and a heuristic search algorithm for registration initialization

Cochlear implants (CIs) use electrode arrays that are surgically inserted into the cochlea to stimulate frequency-mapped nerve endings to treat patients with hearing loss. CIs are programmed postoperatively by audiologists using behavioral tests without information on electrode-cochlea spatial relationship. We have recently developed techniques to segment the intracochlear anatomy and to localize individual contacts in clinically acquired computed tomography (CT) images. Using this information, we have proposed a programming strategy that we call image-guided CI programming (IGCIP), and we have shown that it significantly improves outcomes for both adult and pediatric recipients. One obstacle to large-scale deployment of this technique is the need for manual intervention in some processing steps. One of these is the rough registration of images prior to the use of automated intensity-based algorithms. Although seemingly simple, the heterogeneity of our image set makes this task challenging. We propose a solution that relies on the automated random forest-based localization of multiple landmarks used to estimate an initial transformation with a point-based registration method. Results show that it produces results that are equivalent to a manual initialization. This work is an important step toward the full automation of IGCIP.

Selecting electrode configurations for image-guided cochlear implant programming using template matching

Cochlear implants (CIs) are neural prostheses that restore hearing using an electrode array implanted in the cochlea. After implantation, the CI processor is programmed by an audiologist. One factor that negatively impacts outcomes and can be addressed by programming is cross-electrode neural stimulation overlap (NSO). We have proposed a system to assist the audiologist in programming the CI that we call image-guided CI programming (IGCIP). IGCIP permits using CT images to detect NSO and recommend deactivation of a subset of electrodes to avoid NSO. We have shown that IGCIP significantly improves hearing outcomes. Most of the IGCIP steps are robustly automated but electrode configuration selection still sometimes requires manual intervention. With expertise, distance-versus-frequency curves, which are a way to visualize the spatial relationship learned from CT between the electrodes and the nerves they stimulate, can be used to select the electrode configuration. We propose an automated technique for electrode configuration selection. A comparison between this approach and one we have previously proposed shows that our method produces results that are as good as those obtained with our previous method while being generic and requiring fewer parameters.

Cochlear implant phantom for evaluating computed tomography acquisition parameters

Cochlear implants (CIs) are surgically implantable neuroprosthetic devices used to treat profound hearing loss. Recent literature indicates that there is a correlation between the final intracochlear positioning of the CI electrode arrays and the ultimate hearing outcome of the patient, indicating that further studies to better understand the relationship between electrode position and outcomes could have significant implications for future surgical techniques, array design, and processor programming methods. Postimplantation high-resolution computed tomography (CT) imaging is the best modality for localizing electrodes and provides the resolution necessary to visually identify electrode position, although with an unknown degree of accuracy depending on image acquisition parameters, like the hounsfield unit (HU) range of reconstruction, orientation, radiation dose, and image resolution. We report on the development of a phantom and on its use to study how four acquisition parameters, including image resolution and HU range of reconstruction, affect how accurately the true position of the electrodes can be found in a dataset of CT scans acquired from multiple helical and cone beam scanners. We also show how the phantom can be used to evaluate the effect of acquisition parameters on automatic electrode localization techniques.

Atlas-Based Segmentation of Temporal Bone Anatomy

PURPOSE

To develop a time-efficient automated segmentation approach that could identify critical structures in the temporal bone for visual enhancement and use in surgical simulation software.

METHODS

An atlas-based segmentation approach was developed to segment the cochlea, ossicles, semicircular canals (SCCs), and facial nerve in normal temporal bone CT images. This approach was tested in images of 26 cadaver bones (13 left, 13 right). The results of the automated segmentation were compared to manual segmentation visually and using DICE metric, average Hausdorff distance, and volume similarity.

RESULTS

The DICE metrics were greater than 0.8 for the cochlea, malleus, incus, and the SCCs combined. It was slightly lower for the facial nerve. The average Hausdorff distance was less than one voxel for all structures, and the volume similarity was 0.86 or greater for all structures except the stapes.

CONCLUSIONS

The atlas-based approach with rigid body registration of the otic capsule was successful in segmenting critical structures of temporal bone anatomy for use in surgical simulation software.

Electrode Location and Audiologic Performance After Cochlear Implantation: A Comparative Study Between Nucleus CI422 and CI512 Electrode Arrays

OBJECTIVES

1) Compare rates of scala tympani (ST) insertion between Nucleus CI422 Slim Straight electrodes and Nucleus CI512 Contour Advance electrodes; 2) examine audiometric performance with both electrode arrays, while controlling for electrode location.

SETTING

Tertiary academic hospital.

PATIENTS

Fifty-six post-lingually deafened adults undergoing cochlear implant (CI).

MAIN OUTCOME MEASURES

Primary outcome measures of interest were scalar electrode location and postoperative audiologic performance.

RESULTS

Fifty-six implants in 49 patients were included; 20 were implanted with Nucleus CI422 Slim Straight electrodes, and 36 were implanted with Nucleus CI512 Contour Advance electrodes. Overall, 62.5% (35 of 56) of implants had all electrodes located within the ST. Significantly, higher rates of ST insertion (90%) were observed for Nucleus CI422 Slim Straight electrodes when compared with Nucleus CI512 Contour Advance electrodes (47.2%) (p = 0.002). In regards to audiologic performance, consonant-nucleus-consonant (CNC) scores were significantly higher for Nucleus CI422 Slim Straight electrodes (55.4%) compared with Nucleus CI512 Contour Advance electrodes (36.5%) (p = 0.005). In addition, AzBio scores were better for Nucleus CI422 Slim Straight electrodes (71.2%) when compared with Nucleus CI512 Contour Advance electrodes (46.7%) (p = 0.004). Controlling for ST insertion, higher AzBio scores were again observed for Nucleus CI422 Slim Straight electrodes (p = 0.02).

CONCLUSIONS

The results of this study demonstrate that the Nucleus CI422 Slim Straight electrode is more likely to reside entirely within the ST when compared with the Nucleus CI512 Contour Advance electrode. Furthermore, AzBio scores were superior for patients with Nucleus CI422 Slim Straight electrodes in all patients, as well as those with only ST insertions.

Tip Fold-over in Cochlear Implantation: Case Series

OBJECTIVE

To describe the incidence, clinical presentation, and performance of cochlear implant (CI) recipients with tip fold-over.

STUDY DESIGN

Retrospective case series.

SETTING

Tertiary referral center.

PATIENTS

CI recipients who underwent postoperative computed tomography (CT) scanning.

INTERVENTION(S)

Tip fold-over was identified tomographically using previously validated software that identifies the electrode array. Electrophysiologic testing including spread of excitation or electric field imaging (EFI) was measured on those with fold-over.

MAIN OUTCOME MEASURE(S)

Location of the fold-over; audiological performance pre and postselective deactivation of fold-over electrodes.

RESULTS

Three hundred three ears of 235 CI recipients had postoperative CTs available for review. Six (1.98%) had tip fold-over with 5/6 right-sided ears. Tip fold-over occurred predominantly at 270 degrees and was associated with precurved electrodes (5/6). Patients did not report audiological complaints during initial activation. In one patient, the electrode array remained within the scala tympani with preserved residual hearing despite the fold-over. Spread of excitation supported tip fold-over, but the predictive value was not clear. EFI predicted location of the fold-over with clear predictive value in one patient. At an average follow-up of 11 months, three subjects underwent deactivation of the overlapping electrodes with two of them showing marked audiological improvement.

CONCLUSION

In a large academic center with experienced surgeons, tip fold-over occurred at a rate of 1.98% but was not immediately identifiable clinically. CT imaging definitively showed tip fold-over. Deactivating involved electrodes may improve performance possibly avoiding revision surgery. EFI may be highly predictive of tip fold-over and can be run intraoperatively, potentially obviating the need for intraop fluoroscopy.

Automatic Cochlear Duct Length Estimation for Selection of Cochlear Implant Electrode Arrays

HYPOTHESIS

Cochlear duct length (CDL) can be automatically measured for custom selection of cochlear implant (CI) electrode arrays.

BACKGROUND

CI electrode array selection can be influenced by measuring the CDL, which is estimated based on the length of the line that connects the round window and the lateral wall of the cochlea when passing through the modiolus. CDL measurement remains time consuming and inter-observer variability has not been studied.

METHODS

We evaluate an automatic approach to directly measure the two-turn (2T) CDL using existing algorithms for localizing cochlear anatomy in computed tomography (CT). Pre-op CT images of 309 ears were evaluated. Two fellowship-trained neurotologists manually and independently measured CDL. Inter-observer variability between measurements across expert and automatic observers is assessed. Inter-observer differences for choice of electrode type are also investigated.

RESULTS

Manual measurement of CDL by experts tends to underestimate cochlea size and has high inter-observer variability, with mean absolute differences between expert CDL estimations of 1.15 mm. Our results show that this can lead to a large number of cochleae for which a different electrode array type would be selected by different observers, depending on the specific threshold value of CDL used to decide between array type.

CONCLUSION

Choosing the best CI electrode array is an important task for optimizing hearing outcomes. Manual cochleae length measurements are user-dependent, and errors impact upon the CI electrode array choice for certain patients. Measuring cochlea length automatically is less time consuming and generates more repeatable results. Our automatic approach could make use of CDL for patient-customized treatment more clinically adoptable.

Evaluation of Rigid Cochlear Models for Measuring Cochlear Implant Electrode Position

OBJECTIVE

To investigate the accuracy of rigid cochlear models in measuring intra-cochlear positions of cochlear implant (CI) electrodes.

PATIENTS

Ninety three adults who had undergone CI and pre- and postoperative computed tomographic (CT) imaging.

MAIN OUTCOME MEASURES

Seven rigid models of cochlear anatomy were constructed using micro-CTs of cochlear specimens. Using each of the seven models, the position of each electrode in each of the 98 ears in our dataset was measured as its depth along the length of the cochlea, its distance to the basilar membrane, and its distance to the modiolus. Cochlear duct length was also measured using each model.

RESULTS

Standard deviation (SD) across rigid cochlear models in measures of electrode depth, distance to basilar membrane, distance to modiolus, and length of the cochlear duct at two turns were 0.68, 0.11, 0.15, and 1.54 mm. Comparing the estimated position of the electrodes with respect to the basilar membrane, i.e., deciding whether an electrode was located within the scala tympani (ST) or the scala vestibuli (SV), there was not a unanimous agreement between the models for 19% of all the electrodes. With respect to the modiolus, each electrode was classified into one of the three groups depending on its modiolar distance: close, medium, and far. Rigid models did not unanimously agree on modiolar distance for approximately 50% of the electrodes tested.

CONCLUSIONS

Inter-model variance of rigid cochlear models exists, demonstrating that measurements made using rigid cochlear models are limited in terms of accuracy because of non-rigid inter-subject variations in cochlear anatomy.

Evaluation of a high-resolution patient-specific model of the electrically stimulated cochlea

Cochlear implants (CIs) are surgically implanted medical devices used to treat individuals with severe-to-profound sensorineural hearing loss. Although these devices have been remarkably successful at restoring audibility, many patients experience poor outcomes. Our group has developed the first image-guided CI programming technique where the electrode positions are found in CT images and used to estimate neural activation patterns, which is unique information that audiologists can use to define patient-specific processor settings. Currently, neural activation is estimated using only the distance from each electrode to the neural activation sites, which might be less accurate than using high-resolution electro-anatomical models (EAMs) to perform physics-based estimations of neural activation. We propose a patient-customized EAM approach where the EAM is spatially and electrically adapted to a patient-specific configuration. Spatial adaptation is done through nonrigid registration of the model with the patient CT image. Electrical adaptation is done by adjusting tissue resistivity parameters, so the intracochlear voltage distributions predicted by the model best match those directly measured for the patient via their implant. We found that our approach, demonstrated for [Formula: see text] patients, results in mean percent differences between direct and simulated measurements of voltage distributions of 10.9%.

Retrospective Evaluation of a Technique for Patient-Customized Placement of Precurved Cochlear Implant Electrode Arrays

Objective Precurved electrode arrays (EAs) are commonly used in cochlear implants (CIs). Modiolar placement of such arrays has been shown to lead to better hearing outcomes. In this project, we retrospectively evaluated the modiolar positioning of EAs within a large CI imaging database. We aimed to discover the rate at which perimodiolar placement is successfully achieved and to evaluate a new technique we propose to preoperatively plan patient-customized EA insertion depths to improve perimodiolar placement at the time of surgery. Study Design Retrospective chart review and radiographic analysis. Setting Single tertiary academic referral center. Subjects and Methods Ninety-seven CI ears were evaluated. Perimodiolar positioning of electrodes was quantified using pre- and postimplantation computed tomography scans and automated image analysis techniques. Results Average perimodiolar distance was 0.59 ± 0.18 mm. Disagreement between the actual and our recommended insertion depth was found to be positively correlated with perimodiolar distance ( r = 0.49, P < .0001). Conclusions These results show that the average CI recipient with a precurved EA has a number of electrodes distant to the modiolus where they are not most effective. Our results also indicate the approach we propose for selecting patient-customized EA insertion depth would lead to better perimodiolar placement of precurved EAs.

Insertion depth impacts speech perception and hearing preservation for lateral wall electrodes

OBJECTIVES

1) Examine angular insertion depths (AID) and scalar location of Med-El (GmbH Innsbruck, Austria) electrodes; and 2) determine the relationship between AID and audiologic outcomes controlling for scalar position.

STUDY DESIGN

Retrospective review.

METHODS

Postlingually deafened adults undergoing cochlear implantation with Flex 24, Flex 28, and Standard electrode arrays (Med-El) were identified. Patients with preoperative and postoperative computed tomography scans were included so that electrode location and AID could be determined. Outcome measures were 1) speech perception in the cochlear implant (CI)-only condition, and 2) short-term hearing preservation.

RESULTS

Forty-eight implants were included; all electrodes (48 of 48) were positioned entirely within the scala tympani. The median AID was 408° (interquartile [IQ] range 373°-449°) for Flex 24, 575° (IQ range 465°-584°) for Flex 28, and 584° (IQ range 368°-643°) for Standard electrodes (Med-El). The mean postoperative CNC score was 43.7% ± 21.9. A positive correlation was observed between greater AID and better CNC performance (r = 0.48, P < 0.001). Excluding patients with postoperative residual hearing, a strong correlation between AID and CNC persisted (r = 0.57, P < 0.001). In patients with preoperative residual hearing, mean low-frequency pure-tone average (PTA) shift was 27 dB ± 14. A correlation between AID and low-frequency PTA shift at activation was noted (r = 0.41, P = 0.04).

CONCLUSION

Favorable rates of scala tympani insertion (100%) were observed. In the CI-only condition, a direct correlation between greater AID and CNC score was noted regardless of postoperative hearing status. Deeper insertions were, however, associated with worse short-term hearing preservation. When patients without postoperative residual hearing were analyzed independently, the relationship between greater insertion depth and better performance was strengthened.

LEVEL OF EVIDENCE

4. Laryngoscope, 127:2352-2357, 2017.

Micro-CT versus synchrotron radiation phase contrast imaging of human cochlea

High-resolution images of the cochlea are used to develop atlases to extract anatomical features from low-resolution clinical computed tomography (CT) images. We compare visualization and contrast of conventional absorption-based micro-CT to synchrotron radiation phase contrast imaging (SR-PCI) images of whole unstained, nondecalcified human cochleae. Three cadaveric cochleae were imaged using SR-PCI and micro-CT. Images were visually compared and contrast-to-noise ratios (CNRs) were computed from n = 27 regions-of-interest (enclosing soft tissue) for quantitative comparisons. Three-dimensional (3D) models of cochlear internal structures were constructed from SR-PCI images using a semiautomatic segmentation method. SR-PCI images provided superior visualization of soft tissue microstructures over conventional micro-CT images. CNR improved from 7.5 ± 2.5 in micro-CT images to 18.0 ± 4.3 in SR-PCI images (p < 0.0001). The semiautomatic segmentations yielded accurate reconstructions of 3D models of the intracochlear anatomy. The improved visualization, contrast and modelling achieved using SR-PCI images are very promising for developing atlas-based segmentation methods for postoperative evaluation of cochlear implant surgery.

Initial Results With Image-guided Cochlear Implant Programming in Children

HYPOTHESIS

Image-guided cochlear implant (CI) programming can improve hearing outcomes for pediatric CI recipients.

BACKGROUND

CIs have been highly successful for children with severe-to-profound hearing loss, offering potential for mainstreamed education and auditory-oral communication. Despite this, a significant number of recipients still experience poor speech understanding, language delay, and, even among the best performers, restoration to normal auditory fidelity is rare. Although significant research efforts have been devoted to improving stimulation strategies, few developments have led to significant hearing improvement over the past two decades. Recently introduced techniques for image-guided CI programming (IGCIP) permit creating patient-customized CI programs by making it possible, for the first time, to estimate the position of implanted CI electrodes relative to the nerves they stimulate using CT images. This approach permits identification of electrodes with high levels of stimulation overlap and to deactivate them from a patient's map. Previous studies have shown that IGCIP can significantly improve hearing outcomes for adults with CIs.

METHODS

The IGCIP technique was tested for 21 ears of 18 pediatric CI recipients. Participants had long-term experience with their CI (5 mo to 13 yr) and ranged in age from 5 to 17 years old. Speech understanding was assessed after approximately 4 weeks of experience with the IGCIP map.

RESULTS

Using a two-tailed Wilcoxon signed-rank test, statistically significant improvement (p < 0.05) was observed for word and sentence recognition in quiet and noise, as well as pediatric self-reported quality-of-life (QOL) measures.

CONCLUSION

Our results indicate that image guidance significantly improves hearing and QOL outcomes for pediatric CI recipients.

Detection of modiolar proximity through bipolar impedance measurements

OBJECTIVES

To test the hypothesis that bipolar electrical impedance measurements in perimodiolar cochlear implants (CIs) may be used to differentiate between perimodiolar insertion technique favoring proximity to the modiolus or lateral wall.

STUDY DESIGN AND METHODS

Bipolar impedances are a measure of electrical resistance between pairs of electrode contacts in a CI. Stimulation is through biphasic pulses at fixed frequency. Impedance measurements were made in real time through sequential sampling of electrode pairs. Perimodiolar electrodes were inserted in temporal bones using one of two techniques: 1) In the standard insertion technique (SIT), the electrode array slides along the lateral wall during insertion. 2) In the Advance Off Stylet (Cochlear Ltd. Sydney) technique (AOS), the electrode maintains modiolar contact throughout the insertion process. A set of 22 insertions were performed in temporal bone specimens using perimodiolar electrode arrays with both AOS and SIT. Buffered saline was used as a substitute for natural perilymph based on similar electrical conductivity properties. Impedance with and without stylet removal were recorded with a 30-second sampling window at final insertion depth.

RESULTS

There is a significant difference in bipolar impedance measures between AOS and SIT, with impedances rising in measurements with stylet removal. Evaluation was based on two-sided analysis of variance considering technique and electrode with P < 0.025.

CONCLUSION

Bipolar electrical impedance can be used to detect relative motion toward the modiolus inside the cochlea. This detection method has the potential to optimize intraoperative placement of perimodiolar electrode arrays during implantation. We anticipate that this will result in lower excitation thresholds and improved hearing outcome.

LEVEL OF EVIDENCE

NA. Laryngoscope, 127:1413-1419, 2017.

Results of Postoperative, CT-based, Electrode Deactivation on Hearing in Prelingually Deafened Adult Cochlear Implant Recipients

OBJECTIVE

To test the use of a novel, image-guided cochlear implant (CI) programming (IGCIP) technique on prelingually deafened, adult CI recipients.

STUDY DESIGN

Prospective unblinded study.

SETTING

Tertiary referral center.

PATIENTS

Twenty-six prelingually deafened adult CI recipients with 29 CIs (3 bilateral).

INTERVENTION(S)

Temporal-bone CT scans were used as input to a series of semiautomated computer algorithms which estimate the location of electrodes in reference to the modiolus. This information was used to selectively deactivate suboptimally located electrodes, i.e., those for which the distance from the electrode to the modiolus was further than a neighboring electrode to the same site. Patients used the new IGCIP program exclusively for 3-5 weeks.

MAIN OUTCOME MEASURE(S)

Minimum Speech Test Battery (MSTB), quality of life (QOL), and spectral modulation detection (SMD).

RESULTS

On average one-third of electrodes were deactivated. At the group level, no significant differences were noted for MSTB measures nor for QOL estimates. Average SMD significantly improved after IGCIP reprogramming, which is consistent with improved spatial selectivity. Using 95% confidence interval data for CNC, AzBio, and BKB-SIN at the individual level, 76 to 90% of subjects demonstrated equivocal or significant improvement. Ultimately 21 of 29 (72.41%) elected to keep the IGCIP map because of perceived benefit often substantiated by improvement on either MSTB, QOL, and/or SMD.

CONCLUSIONS

Knowledge of the geometric relationship between CI electrodes and the modiolus appears to be useful in adjusting CI maps in prelingually deafened adults. Long-term improvements may be observed resulting from improved spatial selectivity and spectral resolution.

3D reconstruction of cochlea using optical coherence tomography

Recently, in vivo visualization of the cochlea and the smaller structures inside of it has been achieved by optical coherence tomography (OCT). This makes it possible to use OCT imaging for diagnosis of diseases such as Meniere's disease through measuring the degree of endolymphatic hydrops. To this end, we present a novel method for 3D segmentation of these cochlear OCT images that is based on superpixels and diffusion maps. The method takes as input grayscale volumetric OCT images and outputs a binary image with the segmented cochlea. We show that the proposed method is suitable for segmenting the data for visualization as well as for preprocessing the data for future automated grading of endolymphatic hydrops.

Preoperative preparation for otologic surgery: temporal bone simulation

PURPOSE OF REVIEW

The field of temporal bone simulation (TBS) has largely focused on the development and validation of simulators as training and assessment tools. As technology has progressed over the years, researchers have, however, envisioned new clinical applications for simulators extending to preoperative surgical planning and case rehearsal. The purpose of this article was to review the current state of the art in TBS and to highlight recent advancements in the field. Because of space limitations, we will limit our discussion to computer-based virtual reality simulators.

RECENT FINDINGS

A review of the recent literature on TBS revealed very limited application of virtual reality simulators for preoperative preparation. Current evidence suggests limitations in fidelity preclude successful patient-specific case rehearsal using virtual reality simulation. Further investigation and clinical evaluation are required to validate its use outside of training and skill assessment.

SUMMARY

This article provides an overview of the current use of virtual reality simulators with emphasis on preoperative planning. We evaluate the limitations of the technology, and discuss potential areas of improvement for the future. More studies are necessary to assess the value of virtual reality simulation for preoperative preparation.

Robot-assisted perception augmentation for online detection of insertion failure during cochlear implant surgery

During the past decade, robotics for cochlear implant electrode array insertion has been limited to manipulation assistance. Going beyond manipulation assistance, this paper presents the new concept of perception augmentation to detect and warn against the onset of intracochlear electrode array tip folding. This online failure detection method uses a combination of intraoperative electrode insertion force data and a predictive model of insertion force profile progression as a function of insertion depth. The predictive model uses statistical characterization of insertion force profiles during normal robotic electrode array insertions as well as the history of intra-operative insertion forces. Online detection of onset of tip folding is achieved using the predictive model as an input into a support vector machine classifier. Results show that the detection of tip folding onset can be achieved with an accuracy of 88% despite the use of intra-operative insertion force data representing incomplete insertion. This result is significant because it allows the surgeon or robot to choose a corrective action for preventing intra-cochlear complications.

Random walks with shape prior for cochlea segmentation in ex vivo μCT

PURPOSE

Cochlear implantation is a safe and effective surgical procedure to restore hearing in deaf patients. However, the level of restoration achieved may vary due to differences in anatomy, implant type and surgical access. In order to reduce the variability of the surgical outcomes, we previously proposed the use of a high-resolution model built from [Formula: see text] images and then adapted to patient-specific clinical CT scans. As the accuracy of the model is dependent on the precision of the original segmentation, it is extremely important to have accurate [Formula: see text] segmentation algorithms.

METHODS

We propose a new framework for cochlea segmentation in ex vivo [Formula: see text] images using random walks where a distance-based shape prior is combined with a region term estimated by a Gaussian mixture model. The prior is also weighted by a confidence map to adjust its influence according to the strength of the image contour. Random walks is performed iteratively, and the prior mask is aligned in every iteration.

RESULTS

We tested the proposed approach in ten [Formula: see text] data sets and compared it with other random walks-based segmentation techniques such as guided random walks (Eslami et al. in Med Image Anal 17(2):236-253, 2013) and constrained random walks (Li et al. in Advances in image and video technology. Springer, Berlin, pp 215-226, 2012). Our approach demonstrated higher accuracy results due to the probability density model constituted by the region term and shape prior information weighed by a confidence map.

CONCLUSION

The weighted combination of the distance-based shape prior with a region term into random walks provides accurate segmentations of the cochlea. The experiments suggest that the proposed approach is robust for cochlea segmentation.

Durability of Hearing Preservation after Cochlear Implantation with Conventional-Length Electrodes and Scala Tympani Insertion

OBJECTIVES

To analyze factors that influence hearing preservation over time in cochlear implant recipients with conventional-length electrode arrays located entirely within the scala tympani.

STUDY DESIGN

Case series with planned chart review.

SETTING

Single tertiary academic referral center.

SUBJECTS AND METHODS

A retrospective review was performed to analyze a subgroup of cochlear implant recipients with residual acoustic hearing. Patients were included in the study only if their electrode arrays remained fully in the scala tympani after insertion and serviceable acoustic hearing (≤80 dB at 250 Hz) was preserved. Electrode array location was verified through a validated radiographic assessment tool. Patients with <6 months of audiologic follow-up were excluded. The main outcome measure was change in acoustic hearing thresholds from implant activation to the last available follow-up.

RESULTS

A total of 16 cases met inclusion criteria (median age, 70.6 years; range, 29.4-82.2; 50% female). The average follow-up was 18.0 months (median, 16.1; range, 6.2-36.4). Patients with a lateral wall electrode array were more likely to have stable acoustic thresholds over time (P < .05). Positive correlations were seen between continued hearing loss following activation and larger initial postoperative acoustic threshold shifts, though statistical significance was not achieved. Age, sex, and noise exposure had no significant influence on continued hearing preservation over time.

CONCLUSIONS

To control for hearing loss associated with interscalar excursion during cochlear implantation, the present study evaluated patients only with conventional electrode arrays located entirely within the scala tympani. In this group, the style of electrode array may influence residual hearing preservation over time.

Integration of high-resolution data for temporal bone surgical simulations

PURPOSE

To report on the state of the art in obtaining high-resolution 3D data of the microanatomy of the temporal bone and to process that data for integration into a surgical simulator. Specifically, we report on our experience in this area and discuss the issues involved to further the field.

DATA SOURCES

Current temporal bone image acquisition and image processing established in the literature as well as in house methodological development.

REVIEW METHODS

We reviewed the current English literature for the techniques used in computer-based temporal bone simulation systems to obtain and process anatomical data for use within the simulation. Search terms included "temporal bone simulation, surgical simulation, temporal bone." Articles were chosen and reviewed that directly addressed data acquisition and processing/segmentation and enhancement with emphasis given to computer-based systems. We present the results from this review in relationship to our approach.

CONCLUSIONS

High-resolution CT imaging ([Formula: see text] voxel resolution), along with unique image processing and rendering algorithms, and structure-specific enhancement are needed for high-level training and assessment using temporal bone surgical simulators. Higher-resolution clinical scanning and automated processes that run in efficient time frames are needed before these systems can routinely support pre-surgical planning. Additionally, protocols such as that provided in this manuscript need to be disseminated to increase the number and variety of virtual temporal bones available for training and performance assessment.

Three-dimensional models of cochlear implants: A review of their development and how they could support management and maintenance of cochlear implant performance

Three-dimensional (3D) computational modeling of the auditory periphery forms an integral part of modern-day research in cochlear implants (CIs). These models consist of a volume conduction description of implanted stimulation electrodes and the current distribution around these, coupled with auditory nerve fiber models. Cochlear neural activation patterns can then be predicted for a given input stimulus. The objective of this article is to present the context of 3D modeling within the field of CIs, the different models, and approaches to models that have been developed over the years, as well as the applications and potential applications of these models. The process of development of 3D models is discussed, and the article places specific emphasis on the complementary roles of generic models and user-specific models, as the latter is important for translation of these models into clinical application.

Tubular manipulators: a new concept for intracochlear positioning of an auditory prosthesis

The aim of this study was to investigate the applicability of tubular manipulators as an actuator mechanism for intracochlear positioning of the electrode array (EA) of a cochlear implant (CI). This is motivated by the vision of an atraumatic insertion of the EA into the inner ear (cochlea) without any damage to the intracochlear structures in combination with a well-defined final position. To realize this, an actuator mechanism is required which allows consideration of the patient-specific anatomy. We propose a tubular manipulator for this task. It consists of three concentric tubes: A straight outer tube serves as a guiding sleeve to enter the inner ear (cochlea) and two additional telescoping, superelastic, helically precurved tubes. By selecting helical tube parameters of both tubes prior insertion, a patient-specific curling behaviour of the tubular manipulator can be achieved. For preliminary investigation, segmentation and skeletonization of 5 human scala tympani were performed to determine their centrelines. These centrelines were considered as individual ideal insertion paths. An optimization algorithm was developed to identify suitable tube set parameters (curvature, diameter, length, torsion, stiffness) as well as configuration parameters (translation and rotation of the 2 inner tubes). Different error values describing the deviation of the shape of the tubes with respect to the insertion path were used to quantify the optimization results. In all cases tube set parameters for a final position within the cochlea were found, while keeping the maximum error below 1mm. These preliminary results are promising in terms of the potential applicability of tubular manipulators for positioning auditory prosthesis inside the scala tympani of the inner ear.

Impact of Intrascalar Electrode Location, Electrode Type, and Angular Insertion Depth on Residual Hearing in Cochlear Implant Patients: Preliminary Results

OBJECTIVE

To evaluate the relationship between intrascalar electrode location, electrode type (lateral wall, perimodiolar, and midscala), and angular insertion depth on residual hearing in cochlear implant (CI) recipients.

SETTING

Tertiary academic hospital.

PATIENTS

Adult CI patients with functional preoperative residual hearing with preoperative and postoperative CT scans.

INTERVENTION

Audiological assessment after CI.

MAIN OUTCOME MEASURES

Electrode location, angular insertion depth, residual hearing post-CI, and word scores with CI (consonant-nucleus-consonant [CNC]).

RESULTS

Forty-five implants in 36 patients (9 bilateral) were studied. Thirty-eight electrode arrays (84.4%) were fully inserted in scala tympani (ST), 6 (13.3%) crossed from ST to scala vestibuli (SV), and 1 (2.2%) was completely in SV. Twenty-two of the 38 (57.9%) with full ST insertion maintained residual hearing at 1 month compared with 0 of the 7 (0%) with non-full ST insertion (p = 0.005). Three surgical approaches were used: cochleostomy (C) 6/44, extended round window (ERW) 8/44, and round window (RW) 30/44. C and ERW were small group to compare with RW approaches. However if we combine C + ERW, then RW has higher chance of full ST insertion (p = 0.014). Looking at the full ST group, neither age, sex, nor electrode type demonstrated statistically significant associations with hearing preservation (p = 0.646, p = 0.4, and p = 0.929, respectively). The median angular insertion depth was 429° (range, 373°-512°) with no significant difference between the hearing and nonhearing preserved groups (p = 0.287).

CONCLUSION

Scalar excursion is a strong predictor of losing residual hearing. However, neither age, sex, electrode type, nor angular insertion depth was correlated with hearing preservation in the full ST group. Techniques to decrease the risk of electrode excursion from ST are likely to result in improved residual hearing and CI performance.