First MRI With New Cochlear Implant With Rotatable Internal Magnet System and Proposal for Standardization of Reporting Magnet-Related Artifact Size

Brazilian Society of Otology task force - cochlear implant ‒ recommendations based on strength of evidence

OBJECTIVE

To make evidence-based recommendations for the indications and complications of Cochlear Implant (CI) surgery in adults and children.

METHODS

Task force members were educated on knowledge synthesis methods, including electronic database search, review and selection of relevant citations, and critical appraisal of selected studies. Articles written in English or Portuguese on cochlear implantation were eligible for inclusion. The American College of Physicians' guideline grading system and the American Thyroid Association's guideline criteria were used for critical appraisal of evidence and recommendations for therapeutic interventions.

RESULTS

The topics were divided into 2 parts: (1) Evaluation of candidate patients and indications for CI surgery; (2) CI surgery - techniques and complications.

CONCLUSIONS

CI is a safe device for auditory rehabilitation of patients with severe-to-profound hearing loss. In recent years, indications for unilateral hearing loss and vestibular schwannoma have been expanded, with encouraging results. However, for a successful surgery, commitment of family members and patients in the hearing rehabilitation process is essential.

Multi-Magnet Cochlear Implant Technology and Magnetic Resonance Imaging: The Safety Issue

Despite the spread of novel-generation cochlear-implant (CI) magnetic systems, access to magnetic resonance imaging (MRI) for CI recipients is still limited due to safety concerns. The aim of this study is to assess and record the experiences of Hires Ultra 3D (Advanced Bionics) recipients who underwent an MRI examination. A multicentric European survey about this topic was conducted focusing on safety issues, and the results were compared with the current literature. We collected a total of 65 MRI scans performed in 9 otologic referral centers for a total of 47 Hires Ultra 3D recipients, including, for the first time, 2 children and 3 teenagers. Preventive measures were represented by scanning time and sedation for children. Head wrapping was used in eight cases, and six of the eight cases received local anesthesia, even if both measures were not needed. Only three patients complained of pain (3/65 examinations, 4.6%) due to the tight head bandage, and one of the three cases required MRI scan interruption. No other adverse events were reported. We believe that these results should encourage MRI execution in accordance with manufacturer recommendations for Ultra 3D recipients.

A Systematic Review of Cochlear Implant-Related Magnetic Resonance Imaging Artifact: Implications for Clinical Imaging

OBJECTIVE

To conduct a systematic review of the existing literature with the aim of evaluating and consolidating the present understanding of strategies for mitigating magnetic resonance imaging (MRI) artifacts related to cochlear implants in adult and pediatric patients, covering both in-vivo and ex-vivo investigations.

DATA SOURCES

A systematic review of MEDLINE-Ovid, Embase, Google Scholar, The Cochrane Library, and Scopus was performed from inception through April 2022. The protocol was registered with PROSPERO before commencement of data collection (CRD CRD42022319651).

REVIEW METHODS

The data were screened and collected by two authors independently, and eligibility was assessed according to Cochrane Handbook and Preferred Reporting Items for Systematic Review and Meta-Analysis recommendations, whereas the quality of the articles was evaluated using the NIH Study Quality Assessment.

RESULTS

The search yielded 2,354 potentially relevant articles, of which 27 studies were included in the final review. Twelve studies looked at 1.5-T MRI, four studies looked at 3-T MRI, eight studies looked at both 1.5 and 3 T, one study looked at 0.2 and 1.5 T, and one study looked at 3- and 7.0-T MRI. Nineteen studies focused on MRI sequences as a means of artifact reduction, nine studies focused on implant magnet positioning, two studies focused on head positioning, and one study focused on both magnet and head positioning. In terms of MRI sequences, diffusion-weighted imaging produced larger artifacts compared with other sequences, whereas fast spin echo/turbo spin echo sequences and fat suppression techniques produced smaller artifacts. The position of the magnet was also found to be important, with a magnet position more than 6.5 cm posterior to the external auditory canal producing the best images with the least distortion. The angle at which the magnet is placed also affects visibility of different brain structures.

CONCLUSION

Proper head positioning, magnet placement at a distance of over 6.5 cm from the external auditory canal, use of spin echo sequences, and fat suppression techniques reduce the size and shape of MRI artifacts.

MRI surveillance after translabyrinthine vestibular schwannoma resection and cochlear implantation: is it feasible?

PURPOSE

Cochlear implantation in patients with vestibular schwannomas is of increasing importance and interest. Two remaining challenges are the assessment of conduction of the cochlear nerve and the possibility of postoperative surveillance with magnetic resonance imaging. The aim of the current study was to assess follow-up imaging and determine the visibility of the internal auditory canal after vestibular schwannoma resection and cochlear implantation as well as in patients with persistent vestibular schwannomas and cochlear implants in place. Visibility of the internal auditory canal, cerebellopontine angle, and labyrinth were evaluated and graded.

METHODS

For this retrospective study, 15 MR examinations of 13 patients after translabyrinthine vestibular schwannoma resection and ipsilateral cochlear implantation were included. All patients had been implanted with an MED-EL cochlear implant. Magnetic resonance imaging was carried out on a 1.5T device. All patients were prepped according to the manufacturer's recommendations.

RESULTS

All 15 examinations were carried out without any adverse event during imaging, such as pain, magnet dislocation, or malfunction. The internal auditory canal and the cerebellopontine angle were sufficiently visible in all cases to allow for vestibular schwannoma follow-up.

CONCLUSION

Magnetic resonance imaging surveillance of the internal auditory canal following vestibular schwannoma resection and cochlear implantation is feasible and safe with modern implants with a 1.5T magnetic resonance imaging device using metal artifact reduction sequences. Necessary follow-up imaging should not be a contraindication for cochlear implantation in patients with vestibular schwannomas.

Feasibility and limitations of head MRI in patients with cochlear implants

OBJECTIVE

Cochlear implants (CIs) were noncompatible with magnetic resonance imaging (MRI) initially; however, recently, implants have become available that are compatible with MRI without the need for magnet removal or bandage fixation. The images produced by MRI scans are sometimes deteriorated by artifacts and are not clinically useful. In this study, we discussed the size differences of such artifacts with respect to the imaging modality and sequences with their clinical validity.

METHODS

We performed a head MRI, using a head bandage and without magnet removal in five patients who underwent cochlear implantation at our department and analyzed the MRI findings.

RESULTS

Without magnet removal, diffusion-weighted images and T2 star-weighted images had larger artifacts and less useful images. T1-weighted images, T2-weighted images (T2WIs), T2-weighted fluid-attenuated inversion recovery (T2-FLAIR) images, and heavy T2WIs could evaluate the unimplanted side and middle of the head but had limited applicability on the CI side.

CONCLUSION

The characteristic features of MRI scan images vary with the method used as well as with the sequence, suggesting that the choice of MRI is largely determined on the basis of clinical feasibility and the requirement. Accordingly, we need to judge well in advance of imaging whether the images would be clinically relevant.

Surgical Versus Noninvasive Manual Repositioning After Cochlear Implant Partial Magnet Dislocation

Objectives: To compare surgical magnet repositioning (SMR) and noninvasive manual magnet repositioning (MMR) as treatments for partial magnet dislocation (PMD) of the internal magnet in a cochlear implant (CI) caused by magnetic resonance imaging (MRI). The primary objective was the success rate, while the secondary objectives were total postinterventional CI downtime and complications. Methods: This single-center retrospective study was conducted at a tertiary referral medical center. Patients with CI treated for PMD between January 1, 2007 and September 30, 2022 were included. SMR served as primary treatment until June 2019 and as secondary treatment after the introduction of MMR. Results: A total of 51 cases of PMD were observed in 42 patients and 43 devices (18 ♀; 24 ♂; 12 with bilateral CI). MMR was performed successfully in 19 out of 20 cases (95%), while 32 cases were managed successfully by SMR. The median age at first magnet repositioning was 53.8 years (minimum 19 years, maximum 93 years). When MMR was performed, the mean time from diagnosis to treatment (0.5 ± 1.5 days vs 9.8 ± 7.6 days; P < .01), the mean time from repositioning to CI reactivation (1.4 ± 4.3 days vs 13.1 ± 6.7 days; P < .01), and the mean total CI downtime (1.9 ± 4.8 days vs 22.9 ± 11.9 days; P < .01) were significantly shorter compared to SMR. Significantly fewer complications were experienced with MMR [n = 0 (0%) vs n = 8 (25%); P = .04]. Conclusion: In case of PMD caused by MRI, noninvasive MMR shows a high success rate with a shorter total CI downtime as well as a lower complication rate compared to SMR. Therefore, MMR should be considered as first line treatment with SMR as a second option in case of failure.

Risk of magnetic resonance imaging-induced magnet dislocation for different types of cochlear implants: a single-center retrospective study

BACKGROUND

When performing magnetic resonance imaging (MRI) in patients with a cochlear implant (CI), complication rates vary widely in the literature. The primary objective of this retrospective study was to determine the prevalence of complications, in particular magnet dislocation, in patients with CI undergoing 1.5 Tesla (T) MRI. As a secondary objective, the prevalence of magnet dislocation for specific cochlear implant device types was elaborated.

METHODS

In a single-center retrospective study, all patients with a cochlear implant presenting for an MRI examination at 1.5 T at our institution between January 1st, 2010 and December 31st, 2020 were included. Implants with axial and diametrical magnets were included in the study. MRI safety measures were applied before imaging. The prevalence of complications was evaluated. Magnet dislocation rates were calculated for device types with at least 20 MRI exposures.

RESULTS

During the study period, 196 MRI examinations were performed in a total of 128 patients, accounting for 149 different implants (21 implanted bilaterally) with a total of 231 implant exposures to MRI (average 1.69 ± 1.57; min. 1, max. 12). Complications were reported in 50 out of 231 cochlear implant exposures (21.6%). Magnet dislocation occurred in a total of 27 cases (11.7%). Dislocation rates were 29.6% for the Cochlear® CI500 series (24 dislocations from 81 exposures), 1.1% for the Cochlear® CI24RE series (1 from 87) and 0% for the MED-EL® Synchrony (0 from 36). The dislocation rate for the CI500 was significantly higher than for the CI24RE (χ²₍₁₎ = 26.86; p < 0.001; ϕ = 0.40) or the Synchrony (χ²₍₁₎ = 13.42; p < 0.001; ϕ = 0.34).

CONCLUSIONS

For 1.5 T MRI, the risk of magnet dislocation ranges from 0 to 29.6% and depends on the CI device type. Implants with a diametrical magnet can be considered potentially MRI-safe, whereas in CIs with axial magnets, the CI500 is at high risk of magnet dislocation. Therefore, apart from a strict indication for an MRI and adherence to safety protocols, post-MRI follow-up examination to rule out magnet dislocation is recommended.

Image Quality and Artifact Reduction of a Cochlear Implant With Rotatable Magnets

OBJECTIVE

To determine if metal reduction magnetic resonance imaging sequences and changes in implant placement minimize artifact from cochlear implants and improve visualization of intracranial structures.

STUDY DESIGN

Cadaveric study.

SETTING

Tertiary referral center.

PATIENTS

Five cadaveric heads.

INTERVENTIONS

Specimens were implanted with Advanced Bionics HiRes Ultra3D devices at nasion-external auditory canal angles of 90, 120, and 160 degrees, and distances from the external auditory canal of 9 or 12 cm. Standard brain/internal auditory canal (IAC) sequences with metal artifact reducing technique were acquired in a 1.5T scanner.

MAIN OUTCOME MEASURES

The primary outcome was visibility of 14 intracranial structures graded on a 4-point scale (1, structures <50% visible; 2, >50% visible with some areas nonvisible from artifact; 3, artifact present but adequate for diagnosis; and 4, high quality). Scores were determined by experienced head and neck radiologists and compared with one-way analysis of variance.

RESULTS

Imaging sequences included axial 5-mm whole-brain turbo spin echo (TSE) T2 with right to left and anterior to posterior encoding, fluid-attenuation inversion recovery high bandwidth, axial 5-mm whole-brain slice-encoding metal artifact correction (SEMAC), axial IAC constructive interference in steady state, and axial 3-mm T1 IAC with and without fat saturation. T1 IACs in axial and coronal planes were best for ipsilateral structures overall (mean [standard deviation {SD}], 3.8 [0.6] and 3.8 [0.5]). SEMAC (mean [SD], 3.5 [0.8]) was superior to TSE with anterior to posterior encoding (mean [SD], 3.5 [0.9) for ipsilateral cortex, cerebellopontine angle, and brainstem/cerebellum, and equivalent for the inner ear. Constructive interference in steady state and T1 with fat saturation were poor for all ipsilateral structures (mean, 2.8 [ p < 0.01]; mean, 3.1 [ p < 0.01]). The 120 degrees/12 cm position was overall best, although the 120 degrees/9 cm position still afforded visualization of ipsilateral structures; other angles and distances conferred slight advantages for specific structures of interest.

CONCLUSIONS

SEMAC and T2 TSE with anterior to posterior encoding sequences provide artifact suppression while retaining excellent image quality. Different placement angles did not confer improvement in visualization, although placement distances provided slight advantages for some structures.

Characterizing Cochlear Implant Magnet-Related MRI Artifact

OBJECTIVE

To evaluate cochlear implant (CI) magnet-related MRI artifact shape and size, as well as imaging indications and clinical adequacy of scans.

METHODS

A retrospective chart review was performed for patients undergoing CI and subsequent MRI head imaging from 2014 to 2020 at a single institution. Indications and adequacy of each scan was recorded, and interpretability compared by indication. Magnet-related artifact size was determined by performing ellipsoid modeling at axial slice of greatest signal loss. Artifact radius in centimeters was calculated for 5 sequence categories, and size compared between sequences, manufacturers, and by time from implantation.

RESULTS

Twenty patients underwent 58 head MRI scans. Approximately 76% of MRIs (n = 44) for 70% of patients (n = 14) were performed for indications known of prior to implantation; the remainder were performed during workup of new issues. Desired structures were interpretable in 23 (52%) of known-indication MRIs and 8 (57%) of new-indication MRIs, without significant difference (P = .751). Magnet-related artifact magnitude, compared to the reference T1-weighted fast spin echo (FSE) (4.47 cm), was similar in T2 FSE (4.57 cm, P = .068) and T1 gradient echo (GRE) sequences (4.79 cm, P = .28), but significantly greater in T2 GRE (6.86, P < .0001) and DWI (7.56 cm, P < .0001) sequences.

CONCLUSIONS

DWI and T2 GRE sequences are less useful in MRI evaluation of CI patients. With a more favorable artifact profile, T1 FSE, T2 FSE, and T1 GRE sequences more likely yield clinically useful information. The large proportion of scans performed for known pathology represents an opportunity to optimize for magnet location preoperatively.

Effect of Head Position and Magnetic Resonance Sequence on Cochlear Implant-Related Artifact Size and Internal Auditory Canal Visibility

HYPOTHESIS

To assess whether cochlear implant (CI)-related magnetic resonance imaging (MRI) artifact and visibility of the internal auditory canal (IAC) can be improved with head positioning and select MRI sequences.

BACKGROUND

CI-related MRI artifact limits the use of CIs in otherwise good candidates because of the need for serial MRIs for monitoring of pathology. This most notably impacts patients with tumors of the cerebellopontine angle and IAC.

METHODS

Two cadaver heads were implanted with either a Med-El CONCERT (fixed magnet) or SYNCHRONY (rotating magnet) device. Each head was imaged in a 1.5T scanner in 11 different positions. The SYNCHRONY-implanted head was also imaged in a 3.0T scanner in seven positions. Artifact size and IAC visibility (graded on a Likert scale) were measured for each head position by a neuroradiologist.

RESULTS

The CONCERT CI produced significantly smaller artifact than the SYNCHRONY CI (effect size, 14.65 mm; p < 0.001). There was no significant difference between CI models in regard to IAC visibility. No head positions were statistically significantly better than neutral position for minimizing artifact size or IAC visibility, although some positions resulted in significantly larger artifact (effect sizes, 2.1-14.3 mm; p < 0.05) or significantly poorer IAC visibility (effect size, 1.4; p < 0.01). The T2 three-dimensional (CISS/FIESTA) sequence demonstrated significantly smaller artifact than T1 sequences, whereas T1 sequences demonstrated significantly better IAC visibility than T2 sequences.

CONCLUSION

Head positioning and magnetic resonance sequence selection impact CI-related artifact size and IAC visibility.

Prospective Evaluation of 3 T MRI Effect on Residual Hearing Function of Cochlea Implantees

Introduction: The approval process for MRI safety of implants includes physical observations and an experimental evaluation in artificial settings to simulate the in vivo effect. This contains the observation of temperature changes and artificial current generation by the magnetic field. From these findings, the safety of an implant and its effect on the patient can be estimated. MRI safety is based on an in vivo evaluation of adverse events after the approval process, but an actual analysis of the effect on different tissues is not followed. The effect of MRI scanning in cochlea implantees on their residual hearing as the correlate of the hair cell function is so far unknown, therefore the aim of the present study was to observe the effect of 3 T MRI on the residual hearing of cochlea implantees. Material and Methods: In this prospective study, we performed a 3 T MRI T2 2D MS Drive sequence in eight cochlea-implanted ears. Before and after the MRI scan, a bone conduction pure tone audiogram (BC PTA) was performed. All cochlea implantees had a pre-scanning threshold of low frequency residual hearing between 20 dB and 65 dB. Results: Low frequency mean residual hearing was not affected by the 3 T T2 2D MS Drive sequence. We observed a pre-scanning threshold at 250 Hz of 42.9 (SD 3.9) dB and for 500 Hz 57.1 (SD 6.4) dB. Post-scanning BC PTA was for 250 Hz 42.1 (SD 3.9) dB and for 500 Hz 57.1 (SD 5.7) dB. Conclusion: 3 T MRI scanning has no significant functional effect on the hair cells in cochlea implantees in low frequencies with a T2 2D MS Drive sequence.

A global survey of healthcare professionals undertaking MRI of patients with cochlear implants: a heterogeneity of practice and opinions

OBJECTIVE

To capture practice and opinions around the current clinical use of MRI in patients with cochlear implants (CIs), and to characterise patient progression from referral to image reporting.

METHODS

An online survey recruited 237 healthcare professionals between 9 December 2019 and 9 September 2020. Descriptive statistics and informal thematic analyses were conducted.

RESULTS

Respondents estimated that approximately 75% of CI users referred for an MRI proceeded to image acquisition, of which ~70% of cases comprised image acquisition on the head and the remaining cases on another area. They estimated that the proportion of these images that were usable was 93 and 99%, respectively. Confidence in most processes was high, with at least two-thirds of respondents reporting to be very or somewhat confident in obtaining consent and acquiring images. Conversely, fewer than half the respondents had the same confidence when splinting and bandaging the implant and troubleshooting any issues arising. Patient safety was rated of paramount importance, with patient comfort a clear second and image quality third.

CONCLUSION

These findings highlight the need for consistent publication of clear, succinct, and standardised operating procedures for scanning patients with CIs and the requirement for regular training of radiographic and radiological healthcare professionals to address the heterogeneity of devices available.

ADVANCES IN KNOWLEDGE

There is a need to improve the communication to radiography and radiology personnel regarding the nature of CIs, the heterogeneity of devices in existence, and the key differences between them. CI users risk being underserved by diagnostic medical imaging.

Customized Cochlear Implant Positioning in a Patient With a Low- Grade Glioma: Towards the Best MRI Artifact Management

OBJECTIVE

To report the personalized decision-making pro- cess adopted for a cochlear implant (CI) candidate requiring magnetic resonance imaging (MRI) brain surveillance.

STUDY DESIGN

Clinical capsule report.

SETTING

Tertiary academic referral center.

PATIENT

A 23-year-old man affected by posttraumatic bilat- eral profound hearing loss, already in radiological follow-up for a suspected small left cuneal low-grade glioma.

INTERVENTIONS

A multidisciplinary approach involving preoperative MRI simulations and 3D printed (3DP) models aiming to adapt the CI position to facilitate MRI brain lesion visibility.

MAIN OUTCOME MEASURES

MRI visibility and surgical approach.

RESULTS

Preoperative MRI scans with the placement of an Ultra 3D CI were performed simulating different implant location to assess the brain lesion visibility in MRI. CI was positioned 9 cm away from the external auditory canal with an angle of 90 degrees. To assess the technical feasibility of the surgical procedure, a patient-specific 3DP head model was produced preoperatively. The postoperative course was uneventful, the patient showed a significant benefit from CI, and the brain lesion was highly visible at the MRI follow-up.

CONCLUSIONS

The employment of strategies aimed at improving the MRI quality in CI recipients still represents a topic requiring attention. Thanks to multidisciplinary team collaboration, in our case, the CI position was successfully determined to allow unhindered MRI visibility of a specific intracranial structure.

A comparison of imaging techniques to measure skin flap thickness in cochlear implant patients to enable pre-operative device selection

OBJECTIVES

Magnetic resonance imaging (MRI)-compatible cochlear implants have weaker internal magnets than non-MRI-compatible devices. Their suitability for individual patients is limited by skin flap thickness, traditionally measured with a needle in the operating theatre. We aimed to establish the accuracy of imaging modalities to measure skin flap thickness pre-operatively, with the goal of streamlining device selection and simplifying the consent process.

METHODS

Skin flap measurements were taken using ultrasound (US), computed tomography (CT) and MRI and compared for agreement with intra-operative needle measurement.

RESULTS

Twenty-seven skin flaps were included. Absolute agreement between needle and imaging methods was low: needle/US: 44.4% (95% confidence interval [CI]: 27.7-62.7), needle/CT: 39.1% (95% CI: 22.2-59.2), needle/MRI: 20.8% (95% CI: 9.2-40.5). However, US and CT showed 95.7% agreement (95% CI: 76.0-99.8) with intraclass correlation of 0.996 (95% CI: 0.991-0.998) and narrow Bland-Altman limits of agreement (-0.37, 0.45 mm). BMI and skin flap thickness showed a significant positive correlation (r_s= 0.664, P = 0.002) but no significant correlation was observed for age (P = 0.659).

DISCUSSION

The high level of agreement between US and CT suggests that there are more accurate measurements of skin flap thickness compared with needle or MRI. Needle measurements are consistently smaller.

CONCLUSION

The use of CT or US should be considered when making pre-operative device choices.

A Review of Reported Adverse Events in MRI-Safe and MRI-Conditional Cochlear Implants

OBJECTIVES

This study looks to examine how the development of diametric magnet cochlear implant devices (CIDs) has affected observed magnetic resonance imaging (MRI)-related adverse events and MRI safety measures.

METHODS

A search of the Food and Drug Administration (FDA) Manufacturer and User Facility Device Experience (MAUDE) database was conducted using the product code "MCM" for "Cochlear implants." Reports were included for analysis if they involved MRI in recipients of cochlear implantation. Included reports were stratified into two cohorts by year: 2010 to 2014 and 2015 to 2020, reflecting the FDA approval of diametric magnet cochlear implants in 2015. Extracted event variables included implant manufacturer, adherence to MRI protocol, patient injuries, and device malfunctions.

RESULTS

The product code search query yielded a total of 27,305 reports, from which 584 reports were included for analysis. From 2010 to 2014, there were 109 adverse events and 30 pre-MRI explantations. Implant displacement was the most common device malfunction (n = 69, 87.3%), and pain was the most common patient injury (n = 16, 53.3%). From 2015 to 2020, there were 566 adverse events and 62 pre-MRI explantations. The most common device malfunction was implant displacement (n = 365, 94.6%) and pain was the most common patient injury (n = 114, 63.3%). Only 64/114 (56.1%) reports after 2015 reported adherence to the recommended MRI protocol. No adverse events occurred in patients with synchrony diametric-magnet CIDs.

CONCLUSION

Despite the advent of FDA-approved MRI-safe diametric magnet devices, implanted patients are still experiencing injury, explantation, and device malfunction, and providers are reporting poor compliance with MRI safety protocols.

MRI-induced artifact by a cochlear implant with a novel magnet system: an experimental cadaver study

PURPOSES

To primarily evaluate MRI-induced effects for Ultra 3D cochlear implantation in human cadavers in terms of artifact generation and MR image quality.

METHODS

Three human cadaveric heads were submitted to imaging after unilateral and bilateral cochlear implantation. The 1.5 T MR examination protocol was chosen in accordance with our institutional protocol for the assessment of brain pathology. The maximal signal void size was measured according to each sequence and plane. Two experienced neuro-radiologists and one experienced otoneurosurgeon independently evaluated the MR image quality findings. A 4-point scale was used to describe the diagnostic usefulness of 14 brain structures.

RESULTS

Shape and size of the artifacts were found to be highly related to MRI sequences and acquisition planes. MRI sequences and processing algorithms affected the ability to assess anatomical visibility. Image quality appeared either high or assessable for diagnostic purposes in 9 out of 14 of the ipsilateral structures, in at least one plane. Anatomical structures contralateral to the cochlear implant were highly visible in all conditions. Artifact intrusion clearly improved after application of metal artifact-reduction techniques. In the case of bilateral cochlear implant, a mutual interaction between the two implant magnets produced an additional artifact.

CONCLUSIONS

We performed the first cadaver study aimed at systematically evaluating the MRI-induced artifacts produced by a cochlear implant with a novel four bar magnet system. Specific brain structures can be assessable for diagnostic purposes under 1.5 T MRI, with the cochlear implant magnet in place.

Magnetic Resonance Imaging in Patients With Hearing Implants - Follow-up on Prevalence and Complications

OBJECTIVE

To examine the number of magnetic resonance imaging (MRI) examinations performed in patients with hearing implants and to quantify side effects or complications related to this procedure.

STUDY DESIGN

Questionnaire.

SETTING

Tertiary referral center, academic hospital.

PATIENTS

One thousand four hundred sixty-onepatients with an implanted hearing system.

INTERVENTION

Patients were asked to complete a questionnaire either during a visit to the clinic (304) or by mail contact (1,157) between February 2018 and March 2019.

MAIN OUTCOME MEASURES

Number of examinations by means of MRI per patient and number of side effects or complications.

RESULTS

A total of 711 questionnaires were returned. After excluding nonvalid information on the questionnaire, 12.8% of patients were identified who had undergone an MRI after having received their hearing implant. Within this group of 91 patients, the most common precaution undertaken was a head bandage (69%). Side effects were mainly pain (37%), followed by anxiety (15%) and tinnitus (9%). The MRI had to be aborted in 14% and dislocation of the magnet occurred in 7% of examinations.

CONCLUSIONS

Our data indicate that patients undergoing hearing implant surgery need better information about the limitations and requirements of MRI. The occurrence of side effects is likely as only half of the patients in our study group were completely free of symptoms. Dislocation of the implant magnet was observed in several cases, hence patients and physicians need to be educated about this potential complication.

The role of cochlear implant positioning on MR imaging quality: a preclinical in vivo study with a novel implant magnet system

Purposes

To investigate the effects for Ultra 3D cochlear implant (CI) positioning on MR imaging quality, looking at a comprehensive description of intracranial structures in cases of unilateral and bilateral CI placement.

Methods

Four CI angular positions (90°, 120°, 135° and 160°) at 9 cm distance from the outer-ear canal were explored. The 1.5 T MRI assessment included our institutional protocol for the investigation of brain pathologies without gadolinium application. Three investigators (two experienced neuroradiologists and one experienced otoneurosurgeon) independently evaluated the MR findings. A 4-point scale was adopted to describe 14 intracranial structures and to determine which CI positioning allowed the best image quality score and how bilateral CI placement modified MRI scan visibility.

Results

A high positive correlation was found between the three blinded observers. Structures situated contralateral from the CI showed high-quality values in all four placements. Structures situated ipsilaterally provided results suitable for diagnostic purposes for at least one position. At 90°, artifacts mainly involved brain structures located cranially and anteriorly (e.g., temporal lobe); on the contrary, at 160°, artifacts mostly influenced the posterior fossa structures (e.g., occipital lobe). For the bilateral CI condition, MR imaging examination revealed additional artifacts involving all structures located close to either CI, where there was a signal void/distortion area.

Conclusions

Suitable unilateral CI positioning can allow the visualization of intracranial structures with sufficient visibility for diagnostic purposes. Bilateral CI positioning significantly deteriorates the anatomical visibility. CI positioning might play a crucial role for patients who need post-operative MRI surveillance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00405-021-07005-y.

Safety of active auditory implants in magnetic resonance imaging

Magnetic resonance imaging (MRI) has become the gold standard for the diagnosis of many pathologies. Using MRI in patients with auditory implants can however raise concerns due to mutual interactions between the implant and imaging device, resulting in potential patient risks. Several implant manufacturers have been working towards more MRI safe devices. Older devices are however often labelled for more stringent conditions, possibly creating confusion with patients and professionals. With this myriad of different devices that are implanted in patients for lifetimes of at least 20 years, it is crucial that both patients and professionals have a clear understanding of the safety of their devices. This work aims at providing an exhaustive overview on the MRI safety of active auditory implants. The available industry standards that are followed by manufacturers are outlined and an overview of the latest scientific developments focusing on the last five years is provided. In addition, based on the analysis of the adverse events reported to the Food and Drug Administration (FDA) and in literature within the past ten years, a systematic review of the most commonly occurring issues for patients with auditory implants in the MRI environment is provided. Results indicate that despite the release of more MRI conditional active hearing implants on the market, adverse events still occur. An extensive overview is provided on the MRI safety of active auditory implants, aiming to increase the understanding of the topic for healthcare professionals and contribute to safer scanning conditions for patients.

Cochlear Implant Magnet Dislocation: Simulations and Measurements of Force and Torque at 1.5T Magnetic Resonance Imaging

OBJECTIVES

Dislocation of the magnet inside the implanted component of a cochlear implant (CI) can be a serious risk for patients undergoing a magnetic resonance imaging (MRI) exam. CI manufacturers aim to reduce this risk either via the design of the implant magnet or magnet housing, or by advising a compression bandage and cover over the magnet. The aim of this study is to measure forces and torque on the magnet for different CI models and assess the effectiveness of the design and preventative measures on the probability of magnet dislocation.

DESIGN

Six CI models from four manufacturers covering all the current CI brands were included. Each model was positioned on a polystyrene head with compression bandage and magnet cover according to the recommendations of the manufacturer and tested for dislocation in a 1.5T whole-body MRI system. In addition, measurements of the displacement force in front of the MRI scanner and torque at the MRI scanner isocenter were obtained.

RESULTS

Chance of CI magnet dislocation was observed for two CI models. The design of the magnet or magnet housing of the other models proved sufficient to prevent displacement of the magnet. The main cause for magnet dislocation was found to be the rotational force resulting from the torque experienced inside the magnet bore, which ranges from 2.4 to 16.2 N between the models, with the displacement force being lower, ranging from 1.0 to 1.8 N.

CONCLUSIONS

In vitro testing shows that two CI models are prone to the risk of magnet dislocation. In these CI models, preparation before MRI with special compression bandage and a stiff cover are of importance. But these do not eliminate the risk of pain and dislocation requiring patient consulting before an MRI exam. Newer models show a better design resulting in a significantly reduced risk of magnet dislocation.

Comparison of bandaging techniques to prevent cochlear implant magnet displacement following MRI

INTRODUCTION

For cochlear implants (CI) with removable magnets, a pressure bandage usually is recommended during MR imaging to avoid magnet dislocation. Nevertheless, this complication is regularly observed despite applying a pressure bandage. The aim of this study was to compare various bandaging techniques to avoid magnet displacement.

MATERIALS AND METHODS

As an experimental model a force measuring stand was developed and validated, on which the process of magnet dislocation could be simulated on a cochlear implant. In a test series with six combinations of cohesive and elastic bandages with different counter pressure elements (CPE), the forces required to induce magnet dislocation against the resistance of a compression bandage was determined. In addition, the inter- and intraindividual variability of the compression bandages was measured for ten different users.

RESULTS

The cohesive bandage had the lowest average holding force of 10.70 N. The elastic bandage developed more than four times the retention force of the cohesive bandage (44.88 N, p < 0.01). By adding a CPE, these values could be increased highly significantly up to factor 3. The optimum combination in terms of fixation force against magnet dislocation was an elastic bandage plus a cylindrical CPE (76.60 N). The data showed a high interindividual variability.

CONCLUSION

Even though most CI manufacturers now offer 3T-conditional implants, a pressure bandage will have to be applied to thousands of patients with previous implant generations to prevent magnet dislocation. We examined for the first time force measurements to compare different bandaging techniques by detecting the holding force of the CI magnet. We were able to identify an optimized combination of a bandage and a CPE to immobilize the CI magnet. However, our data also demonstrated a significant scatter amongst different examiners. Although our data provide valuable data for potential clinical application, future development of the dressing technique is required for human use.

Adverse events in pediatric cochlear implant patients undergoing magnetic resonance imaging

OBJECTIVE

To investigate the prevalence and nature of adverse events in magnetic resonance imaging (MRI) of pediatric cochlear implant (CI) patients.

METHODS

Retrospective chart review at a tertiary pediatric hospital. CI patients who underwent MRI from 2004 through 2019 were identified via our internal radiology database. Comorbidities, CI model, age at MRI, number of MRIs, type of MRIs, indication for MRIs, precautions taken for MRIs, quality of MRIs, anesthesia during MRIs, patient language abilities, and adverse events were recorded from the electronic medical record. The literature was reviewed, and our results were compared to those of previous similar series.

RESULTS

From 2004 to 2019, 12 pediatric patients (17 ears) with CIs underwent 22 MRIs. 12 MRIs were performed in CI patients with retained internal magnet. 4/22 MRIs resulted in morbidity; 2 patients experienced pain requiring MRI abortion, 1 experienced magnet rotation requiring surgical replacement, and 1 underwent operative removal of the magnet prior to the scan with surgical replacement thereafter. 19/22 MRIs were performed to evaluate the brain; 17/22 of the radiologic reports noted limitation of evaluation due to artifact. 18/22 MRIs required the administration of anesthesia. 9 of the 22 MRI events involved 2 patients whose CIs had been without internal magnet in anticipation of future MRI requirement.

CONCLUSIONS

Adverse events affecting pediatric patients with CI can occur as a result of MRI, despite appropriate precautions. Safety requires consideration of factors unique to a pediatric hearing-impaired population. Clinicians must remain informed on best practices and manufacturer recommendations.

Subtotal Petrosectomy and Cochlear Implantation: A Systematic Review and Meta-analysis

IMPORTANCE

Subtotal petrosectomy (STP) has been more frequently performed to prepare ears with unfavorable conditions for cochlear implantation.

OBJECTIVES

To provide an overview of indications for and complications of STP and cochlear implantation and to compare outcomes between single vs multistage procedures and between pediatric vs adult populations.

DATA SOURCES

A search of PubMed, Scopus, Ovid, and the Cochrane Library was performed from the databases' inception to January 23, 2020, for studies evaluating STP for cochlear implantation.

STUDY SELECTION

Studies with a minimum follow-up of 3 months and no missing data regarding postoperative outcomes were included. Of the initial 570 studies identified, 27 (4.7%) met selection criteria.

DATA EXTRACTION AND SYNTHESIS

Two reviewers independently assessed study eligibility according to Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines; discrepancies were resolved by a third reviewer. Extracted data included patient demographics, indications for STP, rates of complications, and cholesteatoma recidivism when applicable. Data were pooled using a random- or a fixed-effects model when appropriate.

MAIN OUTCOMES AND MEASURES

The primary study outcome was rate of global complications stratified by patient- and surgery-level characteristics.

RESULTS

Twenty-seven unique studies with 377 unique patients (54.2% male; mean age, 50.6 [range, 1-99] years) undergoing 397 STP procedures and cochlear implantation were included. Of these procedures, 299 of 394 cases with the information reported (75.9%) were single procedures and 95 (24.1%) were multistage procedures. Of the total 397 STP procedures, most common indications included chronic otitis media (220 cases [55.4%]), previous open mastoid cavity (141 [35.5%]), cholesteatoma (74 [18.6%]), and cochlear ossification (29 [7.3%]). The overall complication rate was 12.4% (95% CI, 9.4%-15.9%); overall cholesteatoma recidivism rate was 9.3% (95% CI, 4.3%-17.1%). Complication rates did not significantly differ based on stage or age of patients. Cases with cholesteatoma more often underwent multistage vs single-stage procedures (23 of 54 [42.6%] vs 35 of 174 [20.1%]).

CONCLUSIONS AND RELEVANCE

Across all age groups, STP has been shown to be an effective surgical operation in preparing an ear with unfavorable conditions for cochlear implantation. The potential indications for which cochlear implantation can be performed have expanded with the use of STP. Presence of cholesteatoma might indicate that a multistage procedure should be performed. Lastly, with complication rates comparable to those in adult patients, STP can be considered in children requiring cochlear implantation to minimize ear-related issues and allow benefit from cochlear implantation.

Cochlear Implants and Magnetic Resonance Imaging: Experience With Over 100 Studies Performed With Magnets in Place

OBJECTIVE

To evaluate adverse events and feasibility of performing 1.5-T MRI in patients with cochlear implants (CI) and auditory brainstem implants (ABI).

SETTING

Single tertiary academic referral center.

PATIENTS

CI and ABI recipients undergoing 1.5-T MRI without internal magnet removal.

INTERVENTION(S)

MRI after tight headwrap application.

MAIN OUTCOME MEASURES

Adverse events, patient tolerance.

RESULTS

A total of 131 MR studies in 79 patients were performed, with a total of 157 study ears. Sixty-one patients (77%) had unilateral devices. Four patients (5%) underwent MRI with ABI magnets in place. Sixteen patients (20%) had MRI-compatible devices that did not require a head wrap. There were no instances of device stimulation, device malfunction, or excessive heating of the receiver-stimulator package. Magnet tilt requiring manual repositioning occurred during seven studies (4.5%) and magnet displacement requiring operative intervention occurred during seven studies (4.5%). Significant pain where imaging had to be discontinued occurred during three episodes (2%). No adverse events were noted among patients who underwent MRI with an MRI-compatible magnet.

CONCLUSIONS

MRI with CI or ABI magnets in place is associated with a low prevalence of adverse events when performed in a controlled setting. Many partial magnet displacements can be corrected with firm manual pressure. Devices with magnets that align with the field within their housing were not associated with any adverse events and do not require immobilization of the magnet during the scan. These may be valuable in patients with known or anticipated need for MRI.

Delivery of drugs, proteins, and nucleic acids using inorganic nanoparticles

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