Magnetic resonance imaging with the Digisonic SP Neurelec cochlear implant

Complications of cochlear implants with MRI scans in different body regions: type, frequency and impact

OBJECTIVES

The aim was to assess the type, frequency and impact of MRI-related complications in patients with cochlear implants (CI) and MRI indications in different body regions.

METHODS

For that purpose, the institutional radiology database of a single tertiary hospital was searched for patients with a CI who underwent MRI between 2001 and 2018. The number of MRI examinations and complications were retrieved from the patient record. Examinations were categorized into five distinct body regions or combinations thereof. Records of CI artifacts in the head also included basic information on diagnostic image quality.

RESULTS

Out of 1017 MRI database entries (examinations) of patients with a CI, 91 records were after implantation (71 patients) and 66 were attempted (no contraindications, 49 patients). In four cases (4/66, 6.1%), the magnet was dislocated and had to be replaced surgically. Three out of four severe complications occurred for examination regions outside the head. Thirteen MRI examinations were aborted due to pain (19.7%) and one because of artifacts-resulting in 48 scans (72.7%) completed successfully (36 patients). All cranial scans featured device artifacts in all sequences, but the majority of them did not affect proper imaging diagnostics in the respective region.

CONCLUSION

This retrospective, single-center analysis of patients with MRI-conditional cochlear implants shows that MRI-related complications were common, at least in models with a fixed magnet, despite appropriate precautions and compliance with the manufacturers' guidelines. MRI examinations of CI patients should therefore be indicated strictly until the exact causes have been clarified.

Brain MRI findings of prelingually deaf children and cochlear implant outcome: Preliminary results

OBJECTIVE

To estimate the incidence of brain abnormalities in a cohort of prelingually deaf children and whether these abnormalities can impact the hearing outcomes of patients eligible for cochlear implantation (CI).

METHODS

We performed a retrospective review of consecutive medical charts of prelingually deaf children under 12 years of age who underwent brain magnetic resonance imaging (MRI) during their preoperative workup for CI surgery. We used the category of auditory performance (CAP) test and the speech intelligibility rating (SIR) test to assess the hearing and speech performance of the children, respectively.

RESULTS

The MRIs of 285 patients, 174 boys and 111 girls with a mean age of 36.4 (±16) months, were evaluated for this study. We identified 31 patients with abnormal findings (10.88%): (17/31) (54.8%) had MRI brain abnormalities, (9/31) (29%) had inner ear anomalies, and (5/31) (16.1%) had both inner ear and brain abnormalities. The most frequent inner ear anomaly was an enlarged vestibular aqueduct, while white matter lesions were the most common brain abnormality. The CAP and SIR mean score of patients with inner ear anomalies was slightly, but not significantly, higher than those of patients with brain abnormalities.

CONCLUSION

CAP and SIR scores were not significantly different in children with brain abnormalities than inner ear anomalies. These patients can still benefit from CI to improve their overall hearing and speech performance.

Cochlear implantation in children with white matter lesions: Prediction of hearing outcomes by multiple regression analysis

Brain magnetic resonance imaging (MRI) white matter lesions have been reported in some preoperative cochlear implant children. However, the role of white matter lesions in predicting the hearing outcome is yet unclear. The present study investigated the outcomes of cochlear implantation (CI) in 40 children with white matter lesions.The data from children with white matter lesions were reviewed in this retrospective study. Based on brain MRI, the patients were divided into 3 groups: mild, moderate, and severe. The children were treated with unilateral CI and monitored for a follow-up period of at least 3 years. The main outcome measures were category of auditory performance (CAP) and speech intelligibility rating (SIR). MRI white matter lesions, age at implant, gender, physical impairment, and cognitive impairment were obtained from a research database to assess the correlation with long-term CAP and SIR outcome by multiple regression analysis.The data of children with white matter lesions were reviewed (18 females and 23 males). The mean age at implantation was 31.6 months. Strikingly, all children obtained better CAP and SIR scores. The age at implantation, brain white matters lesions on MRI, and cognitive and physical disabilities were associated with CAP and SIR scores. Multiple regression established a weak correlation between the degree of white matter lesions on brain MRI and long-term CAP and SIR, while cognitive impairment strongly accounted for long-term CAP and SIR outcome.The majority of the children with brain white matter lesions obtained a satisfactory postoperative effect. The cognitive impairment before CI is a major factor, and such factor should be considered.

A review of the safety of MRI in cochlear implant patients with retained magnets

The number of patients with cochlear implants (CIs) is increasing due to expanding indications, and improving CI services. Furthermore, as the use of imaging increases in clinical medicine, it is increasingly likely that patients with CIs will require a magnetic resonance imaging (MRI) examination during their lifetime. Therefore it is important that clinicians are aware of the safety aspects and manufacturer recommendations for CI patients with retained magnets. This article summarises guidelines from all major CI manufacturers and reviews the published literature on the safety of MRI in CI patients with magnets in situ. The most commonly reported complication of MRI in CI patients was pain. Other significant complications included magnet displacement, depolarisation, and polarity reversal. Artefacts caused by the CI remain an issue, but may be reduced by the use of specific sequences. Manufacturer recommendations should be followed to reduce the risk of complications, although complications may occur even when guidelines are followed. For this reason, the indication for imaging these patients should be reviewed, and patients should be appropriately counselled and consented.

Magnetic resonance imaging after cochlear implants

Introduction

Most cochlear implants are currently compatible with magnetic resonance imaging (MRI) up to 3 T. Nevertheless, this does not completely eliminate the risk of serious accidents. Implant displacements and other adverse events with compatible implants have been reported in the literature.

Case reports

Among the six patients who had MRI after receiving implants at our center, we report three cases with adverse events related to the examination. The first case was complicated by magnet displacement with partial demagnetization. The second case showed total demagnetization, which necessitated removal and reimplantation of the implant. The third case involved severe pain sensation which disrupted the MRI scan. The smallest artifact was found with 3D MRI angiography, and largest artifact was found with diffusion and T2 FLASH.

Discussion

Moving the patient into the MRI apparatus must be supervised by an otorhinolaryngology specialist or an experienced radiologist. It is important to consider the magnetic field directions, so that angle between the implant magnetic fields and the MRI B0 always remains less than or equal to 90°. In addition, we recommend the use of an "arrow drawing" to facilitate the orientation of the magnetic field directions. Furthermore, to prevent magnet displacement, we recommend systematic use of a protective splint in addition to bandaging.

MRI scanning in patients implanted with a round window or stapes coupled floating mass transducer of the Vibrant Soundbridge

Conclusion MRI examinations in patients with an alternatively coupled VSB can lead to unpleasant side-effects. However, the residual hearing was not impaired, whereas the hearing performance with the VSB was decreased in one patient which could be fixed by a surgical revision. Different experiences for the VSB 503 can be expected. Objective To investigate the in vivo effects of MRI scanning on the Vibrant Soundbridge system (VSB) with an alternatively coupled Floating Mass Transducer (FMT). Method Sixty-five VSB (502) implantees were included in this study. Of them, 42 questionnaires could be evaluated with the patients' statements about their medical, otological, and general condition before, during, and after an MRI scan which was indicated for different medical reasons, despite the previous implantation of an alternatively coupled Vibrant Soundbridge System. Results In four patients (9.5%), five MRI examinations were performed. These were done for different indications (e.g. knee and shoulder joint diagnostics). During the scanning, noise and subjectively perceived distortion of the implant were described. A deterioration of the hearing gain with the VSB in place was found in one patient. A decrease of the hearing threshold was not observed.

Significant Artifact Reduction at 1.5T and 3T MRI by the Use of a Cochlear Implant with Removable Magnet: An Experimental Human Cadaver Study

Objective

Cochlear implants (CIs) are standard treatment for postlingually deafened individuals and prelingually deafened children. This human cadaver study evaluated diagnostic usefulness, image quality and artifacts in 1.5T and 3T magnetic resonance (MR) brain scans after CI with a removable magnet.

Methods

Three criteria (diagnostic usefulness, image quality, artifacts) were assessed at 1.5T and 3T in five cadaver heads with CI. The brain magnetic resonance scans were performed with and without the magnet in situ. The criteria were analyzed by two blinded neuroradiologists, with focus on image distortion and limitation of the diagnostic value of the acquired MR images.

Results

MR images with the magnet in situ were all compromised by artifacts caused by the CI. After removal of the magnet, MR scans showed an unequivocal artifact reduction with significant improvement of the image quality and diagnostic usefulness, both at 1.5T and 3T. Visibility of the brain stem, cerebellopontine angle, and parieto-occipital lobe ipsilateral to the CI increased significantly after magnet removal.

Conclusions

The results indicate the possible advantages for 1.5T and 3T MR scanning of the brain in CI carriers with removable magnets. Our findings support use of CIs with removable magnets, especially in patients with chronic intracranial pathologies.

[Magnetic resonance imaging in patients with magnetic hearing implants: overview and procedural management]

BACKGROUND

Every year in Germany approximately 3,500 patients receive a cochlear implant or other hearing implants with an implantable magnet. At the same time more and more patients are examined by magnetic resonance imaging (MRI). For the indications and execution of this imaging modality a number of restrictions and safety measures have to be considered.

METHODS

This article is based on the restrictions of the manufacturers and a selective literature search in PubMed using the following keywords: MRI compatibility/MRI safety + cochlea implant/auditory brainstem implant/Bonebridge/Carina/Esteem/Otomag/Sophono alpha/Vibrand Soundbridge. We included all 20 publications of this search concerning the MRI compatibility of the hearing implants complemented by papers cited in the primary articles.

RESULTS

High electromagnetic field intensities as used in MRI can cause malfunction and dislocation of the implant or the magnet in the device. Older cochlear implants (CI) and the current CIs produced by Advanced bionics without explantation of the magnet, some CI models produced by the company Cochlear and the middle ear implants Carina®/Esteem® (older models) and Vibrant-Soundbridge® are not approved for MRI examinations. Other hearing prostheses are approved for 0.2 T, 1.0 T or 1.5 T MRI and in exceptional circumstances 3 T MRI. Recommendations of the manufacturers have to be followed, notably wearing a head bandage during the imaging procedure. The longitudinal axis of the patient's head has to be to positioned parallel to the main magnetic field of the scanner. The patient may not move the head laterally during the examination. Possible artefacts and the reduced validity of the results of skull MRI have to be considered when evaluating the indications for the examination.

CONCLUSION

For patients wearing hearing implants with an implantable magnet the indications for MRI in devices with MRI certification should be rigorously restricted. Possible defects/dislocation of the implants may occur and the quality of the skull MRI images is reduced. A close contact between the radiologist and the implanting team is required. Other diagnostic procedure options should be exhausted before employing MRI.

Effects and consequences of Digisonic SP cochlear implant on radiotherapy planning

The aim of this study was to assess dose attenuation by a Digisonic SP cochlear implant (CI) and evaluate its impact on treatment planning. The Digisonic CI was irradiated with 6 MV photons. Overall dose attenuation was assessed with MOSFET dosimeters and Gafchromic films. In addition, we evaluated the attenuation of separate CI components. Dose attenuation was also calculated using different radiation treatment planning systems (TPS) softwares and dose calculation algorithms. The CI was placed on a head phantom. Single-beam and multiple-beam plans were evaluated for dose attenuation using two radiation techniques (Conformal and Stereotactic radiotherapy) and four different algorithms (Clarkson, Point Kernel-Superposition, Ray Tracing and Monte Carlo). MOSFET and Gafchromics film showed maximal 6-7.5% radiation dose attenuation, at the center of the CI. Computerized TPS-based dose attenuation by the implant was 4-8.1%, using a single ipsilateral field. No clinically meaningful dose attenuation was found in multiple field plans owing to the contribution of various beam paths with only a couple going through the implant using either conventional conformal or stereotactic treatment plans. Dose attenuation induced by a Digisonic SP CI is about 6%, for single 6 MV photon field. This dose reduction is unlikely to be clinically significant, as single-field radiotherapy plans to this anatomic region are uncommon.

Evaluation of the Digisonic® SP cochlear implant: patient outcomes and fixation system with titanium screws

Cochlear implants have revolutionized the way patients affected by severe hearing loss experience the world. Neurelec developed a fixation system with two titanium screws that requires no skull bone drilling.

Objective

To describe the outcomes and procedure-related details of a series of patients implanted with the Digisonic® SP cochlear implant.

Method

This retrospective study analyzed patients submitted to cochlear implant placement within a period of 18 months. All patients had postlingual hearing impairment. Data was collected from patient charts and standard questionnaires answered by the surgeons in charge of carrying out the procedures.

Results

The six patients offered the Digisonic® SP cochlear implants were operated by experienced surgeons. The procedures took 95 to 203 minutes (mean = 135') to be completed, which is less time than what has been described for other fixation approaches. No complications were recorded and hearing improvement was satisfactory.

Conclusion

The Digisonic® SP cochlear implant developed by Neurelec offered good audiological results for adult patients, shorter surgery time, and no surgical or postoperative complications.

MRI brain abnormalities in cochlear implant candidates: how common and how important are they?

OBJECTIVE

To investigate the incidence of abnormal findings on brain MRI in paediatric cochlear implantation candidates.

METHODS

Retrospective review of brain MRI scans of cochlear implant patients between 2000 and 2009 who underwent MRI brain as part of their pre-operative work-up.

RESULTS

MRI scans of 162 patients were reviewed (76 female patients and 86 male patients). The mean age at time of MRI scan was 3 years 8 months. Abnormalities were detected/ reported in 49 patients (30%). The total number of abnormalities detected was 51 (two patients had two separate abnormalities each). Of the abnormalities 82% could be related to known pre-existing conditions. 18% of the abnormalities were incidental/unexpected. Incidental/unexpected abnormalities were found in 9 patients (6%). Four of the patients with incidental abnormalities required referral and further investigations (2.5%). The most common abnormality detected was white matter changes (70%). All the white matter changes were related to pre-existing known medical conditions.

CONCLUSION

At our institution abnormalities detected by pre-operative brain MRI scans on cochlear implant candidates are common (30%). The majority of abnormalities are related to known pre-existing medical conditions. Incidental findings are rare (4%) and approximately half of them required further investigation or referral.

Magnetic Resonance Imaging Compatibility of the Polymer-based Cochlear Implant

Objectives

In this study, we compared the magnetic resonance (MR) image artifacts caused by a conventional metal-based cochlear implant and a newly developed liquid crystal polymer (LCP)-based device.

Methods

The metal-based cochlear implant system (Nurobiosys Co.) was attached to side of the head of a subject and the LCP-based device was attached to opposite side. In both devices, alignment magnets were removed for safety. Magnetic resonance imaging (MRI) was performed on a widely used 3.0 T and an ultra-high 7.0 T MRI machine. 3.0 and 7.0 T MR images were acquired using T1- and T2^*-weighted gradient echo sequences, respectively.

Results

In the 3.0 T images, the metal-based device on the left side generated the significant amount of artifacts. The MR images in the proximity of the metal package were obscured by the artifacts in both axial and sagittal views. On the other hand, the MR images near the LCP-based device were relatively free from the artifacts and clearly showed the brain structures. 7.0 T MR images showed the more severe distortion in the both sides but the metal-based cochlear implant system caused a much larger obscure area than the LCP-based system.

Conclusion

The novel LCP-based cochlear implant provides a good MRI compatibility beyond present-day cochlear implants. Thus, MR images can be obtained from the subjects even with the implanted LCP-based neural prosthetic systems providing useful diagnostic information. Furthermore, it will be also useful for functional MRI studies of the auditory perception mechanism after cochlear implantations as well as for positron emission tomography-MRI hybrid imaging.

[Guidelines for the performance of MRI in patients with cochlear implants]

The number of patients with cochlear implant increases each year. Most of these patients may undergo MR imaging up to 1.5 Tesla, based on safety recommendations from each of the manufacturers. All external components should be removed for the examination. For three manufacturers providing about 85 % of all implanted devices in Europe, the internal components may be left in place and covered by an external bandage. Strict protocol guidelines must be implemented, especially head positioning in the magnet and within 30 cm from the bore opening. A single manufacturer, providing about 15 % of implanted devices, recommends surgical removal of the internal magnet prior to MR imaging.

Neuroimaging with near-infrared spectroscopy demonstrates speech-evoked activity in the auditory cortex of deaf children following cochlear implantation

Cochlear implants (CI) are commonly used to treat deafness in young children. While many factors influence the ability of a deaf child who is hearing through a CI to develop speech and language skills, an important factor is that the CI has to stimulate the auditory cortex. Obtaining behavioral measurements from young children with CIs can often be unreliable. While a variety of noninvasive techniques can be used for detecting cortical activity in response to auditory stimuli, many have critical limitations when applied to the pediatric CI population. We tested the ability of near-infrared spectroscopy (NIRS) to detect cortical responses to speech stimuli in pediatric CI users. Neuronal activity leads to changes in blood oxy- and deoxy-hemoglobin concentrations that can be detected by measuring the transmission of near-infrared light through the tissue. To verify the efficacy of NIRS, we first compared auditory cortex responses measured with NIRS and fMRI in normal-hearing adults. We then examined four different participant cohorts with NIRS alone. Speech-evoked cortical activity was observed in 100% of normal-hearing adults (11 of 11), 82% of normal-hearing children (9 of 11), 78% of deaf children who have used a CI > 4 months (28 of 36), and 78% of deaf children who completed NIRS testing on the day of CI initial activation (7 of 9). Therefore, NIRS can measure cortical responses in pediatric CI users, and has the potential to be a powerful adjunct to current CI assessment tools.

Multicenter Evaluation of the Digisonic SP Cochlear Implant Fixation System with Titanium Screws in 156 Patients

Objectives:

We describe and evaluate the process of fixation of the Digisonic SP cochlear implant with two titanium screws.

Methods:

The characteristics of this implant allow cochlear implantation using a minimal incision, a subperiosteal pocket, and fixation with two titanium screws, without drilling a custom-fitted seat or creating suture-retaining holes in the skull. The fixation system relies on two tailfins for use of osseo-integratable screws, incorporated into the cochlear implant housing. The first version of this fixation system was modified after a case of device migration: The size of the titanium insert inside the silicone tailfin was increased. Data on 156 patients (8 months to 86 years of age) from a 4-year period in 6 cochlear implantation centers were retrospectively evaluated. Ten patients have undergone bilateral implantation.

Results:

Of 166 implantations, 4 postoperative infections and 1 device failure after head trauma were reported. No cerebrospinal fluid leaks or epidural hematomas were reported. One device migration was observed in the first series; no device migrations occurred in the second series.

Conclusions:

The fixation system with screws embedded in the Digisonic SP involves a fast and simple surgical technique that seems to efficiently prevent implant migration.