Omid Majdani

Automatic Segmentation of Intracochlear Anatomy in Conventional CT

Cochlear implant surgery is a procedure performed to treat profound hearing loss. Clinical results suggest that implanting the electrode in the scala tympani, one of the two principal cavities inside the cochlea, may result in better hearing restoration. Segmentation of intracochlear cavities could thus aid the surgeon to choose the point of entry and angle of approach that maximize the likelihood of successful implant insertion, which may lead to more substantial hearing restoration. However, because the membrane that separates the intracochlear cavities is too thin to be seen in conventional in vivo imaging, traditional segmentation techniques are inadequate. In this paper, we circumvent this problem by creating an active shape model with micro CT (μCT) scans of the cochlea acquired ex vivo. We then use this model to segment conventional CT scans. The model is fitted to the partial information available in the conventional scans and used to estimate the position of structures not visible in these images. Quantitative evaluation of our method, made possible by the set of μCTs, results in Dice similarity coefficients averaging 0.75. Mean and maximum surface errors average 0.21 and 0.80 mm.

Clinical Validation of Percutaneous Cochlear Implant Surgery: Initial Report

Objective: Percutaneous cochlear implant surgery consists of a single drill path from the lateral mastoid cortex to the cochlea via the facial recess. We sought to clinically validate this technique in patients undergoing traditional cochlear implant surgery.

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

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

A true minimally invasive approach for cochlear implantation: high accuracy in cranial base navigation through flat-panel-based volume computed tomography.

Objective: High-precision intraoperative navigation using high-resolution flat-panel volume computed tomography makes feasible the possibility of minimally invasive cochlear implant surgery, including cochleostomy. Conventional cochlear implant surgery is typically performed via mastoidectomy with facial recess to identify and avoid damage to vital anatomic landmarks. To accomplish this procedure via a minimally invasive approach-without performing mastoidectomy-in a precise fashion, image-guided technology is necessary. With such an approach, surgical time and expertise may be reduced, and hearing preservation may be improved. Interventions: Flat-panel volume computed tomography was used to scan 4 human temporal bones. A drilling channel was planned preoperatively from the mastoid surface to the round window niche, providing a margin of safety to all functional important structures (e.g., facial nerve, chorda tympani, incus). Main Outcome Measures: Postoperatively, computed tomographic imaging and conventional surgical exploration of the drilled route to the cochlea were performed. Results: All 4 specimens showed a cochleostomy located at the scala tympani anterior inferior to the round window. The chorda tympani was damaged in 1 specimen-this was preoperatively planned as a narrow facial recess was encountered. Conclusion: Using flat-panel volume computed tomography for image-guided surgical navigation, we were able to perform minimally invasive cochlear implant surgery defined as a narrow, single-channel mastoidotomy with cochleostomy. Although this finding is preliminary, it is technologically achievable.

Hearing Preservation Outcomes with Different Cochlear Implant Electrodes: Nucleus® Hybrid™-L24 and Nucleus Freedom™ CI422

Objectives: In recent years, it has been possible to preserve hearing after cochlear implantation in patients with significant amounts of low-frequency residual hearing. Due to the dimensions and characteristics of the cochlear implants (CIs) Nucleus® Hybrid™-L24 and Nucleus Freedom™ CI422, both can be used to preserve residual hearing. The aim was to investigate the degree and progression of hearing preservation over a longitudinal postoperative period in a large consecutive cohort of implanted patients with preoperative residual hearing who received either the Nucleus Hybrid-L24 or the Nucleus Freedom CI422 implant. The intention was to examine potential characteristics and triggers of resulting postoperative hearing loss which may support a differentiation of CI candidacy criteria for a certain implant type. Methods: A retrospective data analysis of patient files on consecutively implanted subjects presenting with a severe-to-profound sensorineural hearing loss at frequencies >1,500 Hz and substantial residual hearing at frequencies ≤1,500 Hz, implanted with a Nucleus Hybrid-L24 (n = 97) or a CI422 implant (n = 100), was undertaken. A single-subject repeated-measure design comparing the mean threshold shift for pure-tone thresholds under headphones up to 24 months after implantation was used. Results: Hearing preservation is observed in the majority of subjects with either implant (250-1,500 Hz frequency range). Hybrid-L24 patients exhibited a median hearing loss of 10 dB at initial fitting (n = 97) and of 15 dB after 24 months (n = 51). A 14.4-dB decrease in median hearing loss at initial fitting (n = 100) and a 30-dB decrease after 24 months (n = 28) was observed with the CI422 electrode. At initial fitting, 54.6% of the Hybrid-L24 (n = 97) and 49.0% of the CI422 (n = 100) subjects showed a mean threshold shift <15 dB. After 24 months, 58.8% (Hybrid-L24, n = 51) and 28.6% (CI422, n = 28) of the patients showed a mean threshold shift <15 dB. Conclusions: The results indicate that residual hearing was preserved for the majority of implanted patients with the Hybrid-L24 and the CI422 implant. Patients implanted with the Hybrid-L24 implant demonstrate greater stability and less median hearing loss over time than those with the CI422 implant. Assessments of onset and stability of hearing loss prior to implantation are important factors to consider during candidacy evaluation for electrode selection to potentially maximize the performance outcome for each patient.

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

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

Cochlear length determination using Cone Beam Computed Tomography in a clinical setting.

Indications for cochlear implants are determined by audiological and medical considerations. Clinical imaging is therefore an integral element for anatomical evaluation in terms of medical considerations. Several authors have discussed the variability of cochlear shape, especially cochlear length. Cochlear length is, however, an increasingly recognized parameter in terms of preoperative evaluation. This study introduces a methodology to determine individual cochlear length in clinical setting by using Cone Beam Computed Tomography. Cochlear length determination was performed retrospectively with an OsiriX curved 3D Multiplanar Reconstruction tool on subjects who underwent temporal bone imaging from January 2011 to February 2013. Cochlear length was defined as the spiral route from the center-distal point of the bony round window along the lateral wall towards the helicotrema, which is the endpoint of the measurement. Cochlear length was measured in 436 temporal bones (218 left ears, 218 right ears, 218 subjects). The mean cochlear length was 37.6 mm (SD: ± 1.93 mm), median was 37.6 mm, range 32-43.5 mm. The cochlear length had a normal distribution. A significant difference was found between cochlear length by gender (p < .0001), but not between the left and right cochlea (p = .301) or according to age. Consideration of the cochlear length in clinical data may be an insufficiently represented parameter in cochlear implant treatment. Literature shows the impact of electrode insertion depth on residual hearing preservation and speech performance. Individual evaluation of the cochlear implant electrode choice may be the next step in personalized cochlear implant treatment as a valuable addition to existing audiological and surgical evaluation. The cochlear length determination methodology presented herein is a reproducible and clinically available parameter. Indeed, revealing a significant cochlear length span width, especially according to gender differences, may be assumed as hardly ignorable.

Auditory midbrain implant: a combined approach for vestibular schwannoma surgery and device implantation.

Hypothesis: The lateral suboccipital approach is a well-established route for safe removal of vestibular schwannomas in neurofibromatosis Type 2 (NF2) patients. The goal of this study was to assess if this approach can be extended to a lateral supracerebellar infratentorial approach to enable insertion of an auditory midbrain implant (AMI) penetrating array along the tonotopic gradient of the inferior colliculus central nucleus (ICC). Background: The AMI is a new auditory prosthesis designed for penetrating stimulation of the ICC in patients with neural deafness. The initial candidates are NF2 patients who, because of the growth and/or surgical removal of bilateral acoustic neuromas, develop neural deafness and are unable to benefit from cochlear implants. The ideal surgical approach in NF2 patients must first enable safe removal of vestibular schwannomas and then provide sufficient exposure of the midbrain for AMI implantation. Methods: This study was performed on formalin-fixed and fresh cadaver specimens. Computed tomography scan and magnetic resonance imaging were used to study the heads of the specimens and for surgical navigation. Results: The lateral suboccipital craniotomy enabled sufficient exposure of the cerebellopontine angle and internal auditory canal for tumor removal. It could then be extended to a lateral supracerebellar infratentorial approach that provided good exposure of the dorsolateral aspect of the tentorial hiatus and mesencephalon for implantation of the AMI along the tonotopic gradient of the ICC. This approach did not endanger the trochlear nerve or any major midline venous structures in the quadrigeminal cistern. Conclusion: This modified lateral suboccipital approach ensures safe removal of large vestibular schwannomas and provides sufficient exposure of the inferior colliculus for ideal AMI implantation.

Automatic determination of optimal linear drilling trajectories for cochlear access accounting for drill-positioning error.

Cochlear implantation is a surgical procedure in which an electrode array is permanently implanted into the cochlea to stimulate the auditory nerve and allow deaf people to hear. Percutaneous cochlear access, a new minimally invasive implantation approach, requires drilling a single linear channel from the skull surface to the cochlea. The focus of this paper addresses a major challenge with this approach, which is the ability to determine, in a pre‐operative CT, a safe and effective drilling trajectory.

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

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