Contemporary imaging of auditory implants

Advances in auditory implants

Auditory implants are classified into bone conduction (BAHA and Bonebridge; BB) and active middle ear implants (Vibrant Soundbridge; VSB) that stimulate cochlear hair cells, and cochlear implants (CIs) that stimulate neural structures. CIs should be performed as early as possible, and bilateral CIs have become popular because sound localization and speech recognition can be improved. CI is also considered a desirable treatment option for patients with single-sided deafness. VSB provides a safe and effective option for patients with conductive or mixed hearing loss and moderate to severe sensorineural hearing loss (SNHL); however, it use in patients with conductive or mixed hearing loss have only been approved in Japan. BAHA and BB implants have been approved by national insurance in Japan as bone conduction implants for patients with conductive or mixed hearing loss. Two fully implantable devices (Cochlear Carina and Envoy Esteem) are provided for patients with SNHL.

Anatomical Variations of the Epitympanum and the Usable Space for Middle Ear Implants Analyzed With CT-assisted Imaging Using a Tablet-based Software

OBJECTIVE

To evaluate interindividual anatomical variations of the epitympanum and the usable space for implantation of active middle ear implants (AMEI) as well as the usefulness of a tablet-based software to assess individual anatomy on computed tomography (CT) scans.

PATIENTS

CT scans of 126 patients, scheduled for cochlea implantation (50.8% men; 0.6-90.0 yr) without middle ear malformations or previous middle ear surgery and with slice thickness ≤0.7 mm were analyzed.

MAIN OUTCOME MEASURES

Since no standardized measurements to assess the size of the epitympanum are available, relevant distances were defined according to anatomical landmarks. Three independent raters measured these distances using a tablet-based software. Interrater correlation was computed to evaluate the quality of the measurement process. Descriptive data were analyzed for validation and for evaluation of interindividual anatomical variations. Influence of age and sex on the taken measurements was assessed.

RESULTS

No relevant correlation between age or sex and the anatomy of the epitympanum was found. Interrater correlation ranged from Spearman's ρ = 0.3-0.9 and there were significant differences between individual rater results for various combinations. Descriptive data revealed high interindividual anatomical variance of the epitympanum, especially regarding the distance between incus and skull base.

CONCLUSION

The reported descriptive data regarding the anatomy of the epitympanum emphasizes the importance of preoperative planning, especially since the height of the epitympanum showed great interindividual variance potentially limiting implantation of AMEIs. The herein used tablet-based software seems to be convenient for preoperative assessment of individual anatomy in the hand of otosurgeons.

High-Resolution CT Imaging of the Temporal Bone: A Cadaveric Specimen Study

Objective  Super-high and ultra-high spatial resolution computed tomography (CT) imaging can be advantageous for detecting temporal bone pathology and guiding treatment strategies. Methods  Six temporal bone cadaveric specimens were used to evaluate the temporal bone microanatomic structures utilizing the following CT reconstruction modes: normal resolution (NR, 0.5-mm slice thickness, 512 ² matrix), high resolution (HR, 0.5-mm slice thickness, 1,024 ² matrix), super-high resolution (SHR, 0.25-mm slice thickness, 1,024 ² matrix), and ultra-high resolution (UHR, 0.25-mm slice thickness, 2,048 ² matrix). Noise and signal-to-noise ratio (SNR) for bone and air were measured at each reconstruction mode. Two observers assessed visualization of seven small anatomic structures using a 4-point scale at each reconstruction mode. Results  Noise was significantly higher and SNR significantly lower with increases in spatial resolution (NR, HR, and SHR). There was no statistical difference between SHR and UHR imaging with regard to noise and SNR. There was significantly improved visibility of all temporal bone osseous structures of interest with SHR and UHR imaging relative to NR imaging ( p  < 0.001) and most of the temporal bone osseous structures relative to HR imaging. There was no statistical difference in the subjective image quality between SHR and UHR imaging of the temporal bone ( p  ≥ 0.085). Conclusion  Super-high-resolution and ultra-high-resolution CT imaging results in significant improvement in image quality compared with normal-resolution and high-resolution CT imaging of the temporal bone. This preliminary study also demonstrates equivalency between super-high and ultra-high spatial resolution temporal bone CT imaging protocols for clinical use.

Effect of Sigmoid Sinus Position on the Difficulty and Approaches to Cochlear Implantation Surgery

OBJECTIVES

To assess the effect of the position of the SS on CI regarding the ability to perform posterior tympanotomy, round window visibility, and mastoid pneumatization.

MATERIALS AND METHODS

This is a prospective study, including 65 adult patients with CI performed at our center during 2017. We used 3 methods to assess SS position using a computed tomography (CT) scan. Lee's line passing through the tympanic segment of the facial nerve. Park's line passing through the facial nerve and round window membrane. Our proposed method using a parallel line from the external auditory canal and passing through the facial nerve. Relation to mastoid pneumatization on CT and to intraoperative round window visibility were assessed in relation to intraoperative position of the SS.

RESULTS

The method by Park et al. was statistically significant (p<0.001); however, a cutoff point could not be set. Lee's method was statistically insignificant (p=0.091). Our proposed method was statistically significant with a cutoff point at ≤2.46 mm (p=0.001). SS position did not affect pneumatization nor round window visibility.

CONCLUSION

The position of SS preoperatively using a CT might suggest the inability to perform posterior tympanotomy and the need to change side or approach. However, it does not affect neither mastoid pneumatization nor visibility of the round window niche through the facial recess.

Utilization of SEMAC-VAT MRI for Improved Visualization of Posterior Fossa Structures in Patients With Cochlear Implants

OBJECTIVE

The number of cochlear implant (CI) users is ever increasing worldwide, as is the utilization of magnetic resonance imaging (MRI) as a key diagnostic modality for pathology of the brain and surrounding structures. Despite advances in MRI compatibility with CI, metal artefact remains a significant issue that needs to be addressed. We test our hypothesis that the slice encoding for metal artefact correction and view angle tilting (SEMAC-VAT) metal artefact reduction technique improves demonstration of posterior fossa structures on MRI in CI recipients.

STUDY DESIGN

A retrospective case review.

SETTING

A tertiary referral hearing implant and skull base center.

INTERVENTIONS

Dedicated MRI of the posterior fossa using T1 spin echo post-gadolinium sequences with and without the application of SEMAC-VAT in CI recipients.

MAIN OUTCOME MEASURES

Extent and severity of the artefact and visualization of surrounding anatomic structures with and without the application of SEMAC-VAT, allowing for direct comparison.

RESULTS

Eight CI recipients with nine CI devices were analyzed. We noted a significant reduction in signal void and improved visibility of the ipsilateral hemisphere in every case. Penumbra size increased although there was improved visibility through the penumbra. There was improved visualization of key intracranial structures, such as the ipsilateral internal auditory canal, cerebellopontine angle, cerebellar hemisphere, and brainstem.

CONCLUSIONS

Application of SEMAC-VAT produces a significant reduction in signal void and improved visualization of key structures within the temporal bone and posterior cranial fossa in patients with CIs without the need for removal of the internal magnet.

Validation and Precision of Mixed Reality Technology in Baha Attract Implant Surgery

OBJECTIVE

To test the feasibility of image-guided Baha Attract implant surgery with mixed reality (MR) in the form of the HoloLens to visualize critical structures and facilitate precise Baha implant placement.

METHODS

A cadaveric case study of bilateral Baha Attract implant approaches was conducted using Star Atlas MR three-dimensional (3D) medical interaction system guidance at the Otolaryngology Department of PUMCH, Beijing, China. The accuracy of visual surface registration was determined by the target registration error (TRE) between the predefined points on the preoperative 3D holographic Baha Attract implant model and the postoperatively reconstructed 3D model.

RESULTS

Bilateral Baha Attract implantation was completed successfully for all four cadaveric heads using the Star Atlas MR 3D medical interaction system with the HoloLens. The preoperative 3D digital model characteristics (including bone quality and thickness and avoidance of cranial vessels, air cells, and cranial sutures) corresponded well with the 3D model of the actual implantation reconstructed postoperatively. The median TRE of our system was 2.97 mm (ranging from 1.98 to 4.58 mm) in terms of distance and 2.76 degrees (ranging from 0.59 to 6.4 degrees) in terms of angle.

CONCLUSIONS

Applying MR technology in the form of the HoloLens in Baha Attract implant surgery is feasible and could improve the accuracy of the surgery. The described MR system for Baha Attract implantation has the potential to improve the surgeon's confidence, as well as the surgical safety, efficiency, and precision.

Active middle ear implantation: imaging in the pre-operative planning and post-operative assessment of the Vibrant SoundbridgeTM

Active middle ear implants augment sound waves and directly stimulate the middle ear structures. The most frequently utilised active middle ear implant is the Vibrant Soundbridge ^TM (VSB).CT plays a vital role in appropriate patient selection and surgical planning of active middle ear implant surgery. The VSB ^TM offers a number of options for implant placement. The ideal location is influenced by the patient's middle ear and mastoid anatomy as well as the type and severity of the hearing loss. CT provides important information on the surgical access to the middle ear and helps determine the most appropriate implant site by assessing the adjacent middle ear anatomy and the continuity of the ossicular chain. Post-operative active middle ear implant imaging may be indicated in the setting of poor auditory outcomes and when revision surgery is being considered so as to assess for suboptimal implant placement or migration.This pictorial review will describe the VSB ^TM middle ear device and explain the role of imaging in both the pre-operative and post-operative settings.

The Image Fusion Technique for Cochlear Implant Imaging: A Study of its Application for Different Electrode Arrays

OBJECTIVES

To investigate the benefits of the image fusion technique for precise postoperative assessment of intracochlear placement with six different electrode arrays.

STUDY DESIGN

Consecutive retrospective case study.

SETTINGS

Tertiary referral center.

PATIENTS

Analyses of imaging data of 30 patients implanted with six different electrode arrays.

INTERVENTIONS

Electrode reconstructions obtained from postoperative cone-beam computed tomography (CBCT) were overlaid onto preoperative magnetic resonance imaging (MRI) and/or high-resolution computed tomography (HRCT) registrations to create artefact-free images.

MAIN OUTCOME MEASURES

Each electrode's intracochlear position was analyzed with the image fusion reconstructions and compared with the results obtained by CBCT alone. The electrode location was classified according to its position in relation to the basal membrane at four different insertion angles.

RESULTS

In 40 out of 151 measurements (26.5%), the location grading obtained by CBCT alone changed after the assessment with the image fusion reconstructions. A significant association was found between deep insertions (over 360 degrees) and the effectiveness of image fusion (p = 0.019). The difference between the impact of the fusion technique for the basal turn versus the apical part was highly significant (p = 0.001). There was no significant difference between the effectiveness of the image fusion and the different electrodes.

CONCLUSIONS

By utilizing an image fusion technique, a more accurate assessment of electrode placement could be achieved for all types of electrodes. Image fusion was especially beneficial for insertions beyond 360 degrees.

The Insertion Results of a Mid-scala Electrode Assessed by MRI and CBCT Image Fusion

OBJECTIVES

To investigate the results of clinical surgical insertions with a Mid-scala array (HIFocus Mid-Scala Electrode, HFms).

STUDY DESIGN

Consecutive retrospective case study.

SETTINGS

Tertiary referral center.

PATIENTS

Analyses of imaging data of 26 consecutive patients (31 insertions) implanted with the HFms.

INTERVENTION (S)

The evaluation of insertion trauma evoked by a previously validated image fusion technique. Electrode reconstructions from postoperative cone-beam computed tomography (CBCT) were overlaid onto preoperative magnetic resonance imaging (MRI) scans to create artifact-free images.

MAIN OUTCOME MEASURES

The electrode position was quantified in relation to the basilar membrane. Trauma scaling adopted from Eshraghi was used for evaluating insertion trauma. The results of the visual assessment of the postoperative CBCT were compared to those obtained with the fusion technique.

RESULTS

Three insertions had to be excluded due to incompatibility of the imaging data with the fusion software. We found consistent peri- to mid-modiolar placement of the HFms with a mean insertion depth angle of 376°. According to the medical records, a visual examination of the postoperative CBCT indicated that there had been no scala dislocations but when assessed by the image fusion technique, five scala dislocations (17.8%) were found. Additionally, one tip fold-over was detected in the postoperative CBCT even though this was not evident in any intraoperative measurements.

CONCLUSION

HFms showed atraumatic surgical insertion results with consistent mid-modiolar placement. Image fusion enhances the accuracy of the insertion trauma assessment. Routine postoperative imaging is recommended for identifying tip fold-over as well as for quality control and documentation.

Radiological evaluation of inner ear trauma after cochlear implant surgery by cone beam CT(CBCT)

PURPOSE

Cochlear implantation (CI) has been extended to involve younger age group with higher incidence of residual hearing which increases the need of minimizing surgical inner ear trauma. Radiological evaluation for electrode position has been studied yet without assessment of inner ear trauma, our objective is radiological evaluation of post cochlear implantation inner ear trauma MATERIAL AND METHODS: 20 patients with CI for pre lingual SNHL were included in this study. Cone beam CT (CBCT) was used for evaluation of electrode position and assessment of inner ear trauma. A Neuroradiologist and an implant surgeon analyzed the relation of inserted electrode to the intra-cochlear structures, with introduction of novel radiological grading for inner ear trauma.

RESULTS

The mean major cochlear diameter was 8.9 mm, the mean angular depth of insertion was 406.9944 (SD = 165.0559). Ten patients were with no cochlear trauma (grade 0), three patients were grade 1, two patients were grade 2 and five patients were grade 3 inner ear trauma.

CONCLUSION

Radiological evaluation for electrode position should extend to involve assessment of inner ear trauma using relation of the implant to cochlear internal structures which could be performed by CBCT with high resolution and least metallic artifacts.

[Techniques and progress in the imaging of the ear]

Ear and temporal bone imaging is essential for the diagnostic and preoperative management of middle ear lesions. The scanner is the exam of choice to analyze the walls and the contents of the middle ear. MRI is used to characterize the opacities of the middle ear and to evaluate possible neurological complications. Modern imaging techniques allow intraoperative guidance in otological surgery. Hearing implants are not always a contraindication to MRI but require precautions according to the type of implant.