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

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.

The usefulness of the O-MAR algorithm in MRI skull base assessment to manage cochlear implant-related artifacts

Objective

To assess artifact size and MRI visibility when applying the "Orthopedic-Metal Artifact Reduction" (O-MAR) algorithm for cochlear implant (CI) scanning.

Methods

Two volunteers were submitted to 1.5 T MRI with an Ultra 3D CI receiver stimulator placed on their head. Four angular CI orientations were adopted: 90, 120, 135 and 160 degrees. Volunteers were scanned in each condition using T1w and T2w TSE sequences, as well as O-MAR sequences, in both axial and coronal planes. Quantitative comparisons were made of signal void and penumbra extent. Additionally, qualitative evaluations of global image quality, MRI readability with respect to 12 anatomical structures and visibility through the penumbra were undertaken.

Results

After application of the O-MAR protocol, the radius of the signal void reduced from 50.76 mm to 45.43 mm and from 49.22 mm to 40.15 mm on T1w and T2w TSE axial sequences, respectively (p < 0.05). Qualitatively, sequences acquired with O-MAR produced better outcomes in terms of image quality and anatomical depiction. Despite the area of the penumbra being increased for the O-MAR protocol, visibility through penumbra was improved.

Conclusions

Application of O-MAR may provide a complementary strategy to those already in use to obtain diagnostically useful MRI examinations in the presence of a CI, especially in case of skull base diseases requiring MRI monitoring.

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.

Cochlear Implantation in Sporadic Vestibular Schwannoma and Neurofibromatosis Type II

Cochlear implantation offers significantly better hearing outcomes than auditory brainstem implantation in patients with vestibular schwannoma. Neither the primary treatment modality nor the cause of the tumor (neurofibromatosis type 2 related or sporadic) seems to have a significant effect on hearing outcome with cochlear implantation. Some uncertainty remains regarding long-term hearing outcomes; however, cochlear implantation in vestibular schwannoma serves to offer patients, with a functioning cochlear nerve, the probability of open set speech discrimination with a consequent positive impact on quality of life.

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.

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.

Dimensions and forms of artefacts in 1.5 T and 3 T MRI caused by cochlear implants

Cochlear implantation is a standard treatment option due to expanding indications. Cranial magnetic resonance imaging (cMRI) has become a widespread diagnostic tool. Therefore, an increased number of cochlear implant (CI) users are undergoing cMRI scans. This study aimed to investigate the issue of the CI magnet impacting MRI quality and artifacts. 1.5 T and 3 T MRI scans with 4 defined sequences (T2-TSE, T2-TIRM, T1-3D-MPRAGE, and TDI) were performed on a phantom with a CI (SYNCHRONY System by MED-EL Austria) in place. The resulting MRI artifacts were retrospectively compared to MRI artifacts observed in patients with a CI. All images were transferred to AMIRA and visualized by manual segmentation. Usable image quality was achieved in three sequences (T2-TSE, T2-TIRM and T1-mprage). Observed artifacts differed in shape and size depending on the sequence. Maximum diameters of signal void areas ranged from 58 × 108 × 98 mm to 127 × 123 × 153 mm. Image distortions were larger. MRI artifacts caused by the SYNCHRONY system are asymmetric with varying shape, depending on the sequence. The phantom artefacts are similar to those in CI users. Considering the observed asymmetry, the hypothesis of varying implantation locations resulting in varying positions of the signal void area needs to be further investigated.

Influence of head orientation and implantation site of a novel transcutaneous bone conduction implant on MRI metal artifact reduction sequence

Purpose

The use of magnetic resonance imaging (MRI) is often limited in patients with auditory implants because of the presence of metallic components and magnets. The aim of this study was to evaluate the clinical usefulness of a customized MRI sequence for metal artifact suppression in patients with BONEBRIDGETM BCI 602 implants (MED-EL, Innsbruck, Austria), the successor of the BCI 601 model.

Methods

Using our in-house developed and customized metal artifact reduction sequence (SEMAC-VAT WARP), MRI artifacts were evaluated qualitatively and quantitatively. MRI sequences were performed with and without artifact reduction on two whole head specimens with and without the BCI 602 implant. In addition, the influence of two different implantation sites (mastoid versus retrosigmoid) and head orientation on artifact presence was investigated.

Results

Artifact volume was reduced by more than the 50%. Results were comparable with those obtained with the BCI 601, showing no significant differences in the dimensions of artifacts caused by the implant.

Conclusion

SEMAC-VAT WARP was once more proved to be efficient at reducing metal artifacts on MR images. The dimensions of artifacts associated with the BCI 602 are not smaller than those caused by the BCI 601.

Parametric Assessment of the Effect of Cochlear Implant Positioning on Brain MRI Artefacts at 3 T

BACKGROUND

Brain magnetic resonance imaging in patients with cochlear implants (CIs) is impacted by image artefacts.

HYPOTHESIS

The optimal positioning of the CI to minimize artefacts is unknown. This study aimed to characterize the dependence of the extent and distribution of the artefact on CI positioning.

METHODS

Three normally hearing individuals underwent magnetic resonance imaging using a standard T1-weighted 3D sequence. Scans were acquired with a non-functioning CI placed underneath a swimming cap at four plausible scalp positions on each side, and without the CI in situ. The artefact in each image was assessed quantitatively using voxel-based techniques. Two radiologists also independently rated the likely impact of the artefact on the detection of pathology for 20 neuroradiological locations.

RESULTS

The procedure was well tolerated. The most postero-inferior CI positions resulted in the smallest apparent artefacts. Radiological evaluations suggested that artefacts would likely limit pathology detection in the ipsilateral temporal, parietal, and occipital lobes, regardless of CI location. Pathology detection in contralateral structures and anterior corpus callosum was rarely affected. Certain CI locations appeared to selectively spare ipsilateral structures, for example, postero-inferior CI locations selectively spared ipsilateral midbrain, deep grey matter, and frontal lobes.

CONCLUSION

A CI placed under a swimming cap is a feasible tool for observing the effect of CI location on image usability within a single subject and potentially informing surgical planning. Regardless of CI placement, artefacts involving ipsilateral parietal, temporal, and occipital lobes severely limited diagnostic image utility. Between 35% and 70% of neuroradiological features were deemed unaffected by the implant.

Safety of 3 Tesla Magnetic Resonance Imaging in Patients with Auditory Brainstem Implants

OBJECTIVE

To evaluate the safety of 3 Tesla (T) magnetic resonance imaging (MRI) in patients with auditory brainstem implants (ABI) with the magnet removed at implantation and report incidence of complications.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary neurotology ambulatory practice.

PATIENTS

Patients with diagnosis of Neurofibromatosis, type 2 (NF2) with functional ABIs.

INTERVENTIONS

Observational recordings.

MAIN OUTCOME MEASURES

Of the 89 patients meeting inclusion criteria, 7 patients underwent 3T MRI, with a total of 39 scans done. Three patients had 1 scan each, one patient had 4 scans, one patient had 5 scans, one patient had 6 scans, and one patient had 21 scans. The mean time between ABI placement and first 3 T scan was 118 ± 73 months. The most common indication for imaging was surveillance of NF2 lesions. The most frequent scans were MRI brain (25.6%), followed by MRI of cervical (15%), thoracic (15%) and lumbar (15%) spine, and MRI IAC (8%). There were no reported complications for any of the scans. No scans were interrupted due to patient discomfort. There were no device malfunctions.

CONCLUSIONS

3 T MRIs are safe in patients with ABIs as long as the magnet is removed. It is recommended that the magnet be removed at the time of implantation in all NF2 patients, who require frequent surveillance.

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.

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.

Two-phase survey on the frequency of use and safety of MRI for hearing implant recipients

PURPOSE

Magnetic resonance imaging (MRI) is often used to visualize and diagnose soft tissues. Hearing implant (HI) recipients are likely to require at least one MRI scan during their lifetime. However, the MRI scanner can interact with the implant magnet, resulting in complications for the HI recipient. This survey, which was conducted in two phases, aimed to evaluate the safety and performance of MRI scans for individuals with a HI manufactured by MED-EL (MED-EL GmbH, Innsbruck, Austria).

METHODS

A survey was developed and distributed in two phases to HEARRING clinics to obtain information about the use of MRI for recipients of MED-EL devices. Phase 1 focused on how often MRI is used in diagnostic imaging of the head region of the cochlear implant (CI) recipients. Phase 2 collected safety information about MRI scans performed on HI recipients.

RESULTS

106 of the 126 MRI scans reported in this survey were performed at a field strength of 1.5 T, on HI recipients who wore the SYNCHRONY CI or SYNCHRONY ABI. The head and spine were the most frequently imaged regions. 123 of the 126 scans were performed without any complications; two HI recipients experienced discomfort/pain. One recipient required reimplantation after an MRI was performed using a scanner that had not been approved for that implant. There was only one case that required surgical removal of the implant to reduce the imaging artefact.

CONCLUSION

Individuals with either a SYNCHRONY CI or SYNCHRONY ABI from MED-EL can safely undergo a 1.5 T MRI when it is performed according to the manufacturer's safety policies and procedures.

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.

Assessment of a Novel 3T MRI Compatible Cochlear Implant Magnet: Torque, Forces, Demagnetization, and Imaging

HYPOTHESIS

A novel cochlea implant (CI) device magnet providing alignment to the static field of a magnetic resonance imaging (MRI) will lead to reduced torque, longitudinal forces, and demagnetization effects. The image void and distortion will be comparable to those obtained with standard CI magnets.

BACKGROUND

MRI investigations of CI users pose several challenges such as magnet dislocation, demagnetization, and may cause pain. The presence of a CI magnet within MRI field causes image distortions and may diminish the diagnostic value of an MRI procedure. Objective of this work is to evaluate magnetic forces and imaging properties of the novel CI magnet within 1.5 and 3T MRI.

METHODS

Forces and torque of the novel CI magnet were measured in both 1.5 and 3T MRI and compared with the standard magnet in 1.5T. One cadaver head was implanted with the CI devices containing the novel and standard magnets in different configurations reflecting clinical scenarios and imaging properties were assessed and compared.

RESULTS

In particular the torque has been reduced with the novel CI magnet in comparison to the standard one. Both CI magnets have not shown any signs of demagnetization. The image void and distortion was comparable between the two magnets for the main MRI clinical scanning protocols in 1.5T MRI.

CONCLUSIONS

The novel CI magnet is safe to use for MRI investigations of CI users in 3T MRI without a need for bandaging and has acceptable level of image artefacts.

Heat transfer analysis in an uncoiled model of the cochlea during magnetic cochlear implant surgery

Magnetic cochlear implant surgery requires removal of a magnet via a heating process after implant insertion, which may cause thermal trauma within the ear. Intra-cochlear heat transfer analysis is required to ensure that the magnet removal phase is thermally safe. The objective of this work is to determine the safe range of input power density to detach the magnet without causing thermal trauma in the ear, and to analyze the effectiveness of natural convection with respect to conduction for removing the excess heat. A finite element model of an uncoiled cochlea, which is verified and validated, is applied to determine the range of maximum safe input power density to detach a 1-mm-long, 0.5-mm-diameter cylindrical magnet from the cochlear implant electrode array tip. It is shown that heat dissipation in the cochlea is primarily mediated by conduction through the electrode array. The electrode array simultaneously reduces natural convection due to the no-slip boundary condition on its surface and increases axial conduction in the cochlea. It is concluded that natural convection heat transfer in a cochlea during robotic cochlear implant surgery can be neglected. It is found that thermal trauma is avoided by applying a power density from 2.265 × 10⁷ W/m³ for 114 s to 6.6×10⁷ W/m³ for 9 s resulting in a maximum temperature increase of 6°C on the magnet boundary.

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

OBJECTIVE

To report on the first known magnetic resonance imaging (MRI) with a new cochlear implant (CI) with rotatable internal magnet system, to review the literature on MRI in cochlear implantees, and to advocate for standardization of reporting magnet-related artifact size.

STUDY DESIGN

Case report and review of literature.

SETTING

Tertiary care hospital.

RESULTS

A patient with congenital rubella and bilateral profound hearing loss was incidentally found to have a petroclival meningioma. After resection and radiosurgery, she underwent cochlear implantation with the Advanced Bionics HiRes Ultra 3D device (Advanced Bionics LLC, Valencia, CA) with rotatable internal magnet system, due to need for imaging surveillance of residual meningioma. During 1.5 T MRI brain scan without a head wrap, she experienced no adverse events. The images obtained were adequate for visualization of residual tumor. Implant recipients with non-rotatable magnets who undergo MRI, with or without recommended head wrap, may suffer various complications. All images in patients with retained internal magnets are subject to magnet-related artifact, but reports regarding its size are variable and lack detail on how measurements are made.

CONCLUSIONS

MRI in patients with a new CI device with rotatable magnet system may be performed without discomfort or device dislodgement at 1.5 T, even without a head wrap, though external magnet replacement may require multiple attempts due to internal magnet realignment. Despite significant artifact, the structure of interest may still be visualized for accurate diagnosis. Measuring magnet-related artifact size should be standardized by reporting artifact in radii at the image level of maximal signal loss.

Cochlear Implantation in Neurological Patients: Case Report and Literature Survey

Cochlear implant (CI) is a reliable solution to restore hearing in people with severe-to-profound hearing loss. The device is made up of internal and external components linked transcutaneously through a magnet that may rise specific issues in people who must undergo brain magnetic resonance (MRI) due to neurological diseases. The description of a case of a CI implantee needing MRI has given us the opportunity to highlight the differences that can be encountered among different neuropathies, either acute or chronic, with the aim of shedding some light for finding a common protocol when facing this important and frequent clinical issue. In particular, the removal of the magnet prior to performing an MRI exam is mandatory for brain diseases ipsilateral to the implanted side, whereas for contralateral side lesions it is less important when using apposite bandage kits. Laryngoscope, 131:E576-E580, 2021.

Cochlear Implantation in Patients With Single-sided Deafness After the Translabyrinthine Resection of the Vestibular Schwannoma-Presented at the Annual Meeting of ADANO 2016 in Berlin

OBJECTIVE

To evaluate effectiveness of the cochlear implant (CI) to facilitate single-sided deafness (SSD) rehabilitation following translabyrinthine resection of the vestibular schwannoma.

STUDY DESIGN

Retrospective patient review.

SETTING

Single center, University hospital.

PATIENTS

Patients with SSD who underwent translabyrinthine resection of a vestibular schwannoma with anatomical preservation of the cochlear nerve and subsequent CI on the same ear.

INTERVENTIONS

CI at post-translabyrinthine resection of the acoustic neuroma to treat SSD, and evaluation by retrospective individual case review in a period from 2009 to 2016.

MAIN OUTCOME MEASURES

Individual patients' clinical outcome and speech understanding.

RESULTS

Thirteen patients were provided CI. In all cases, complete removal of the tumor was achieved and the cochlear nerve was preserved; in one case, the CI was implanted simultaneously. In most cases, the follow-up interval was 2 years. In 9 of 13 cases, the implanted ear achieved capability to understand and discriminate monosyllabic words at 65 dB. Level of speech understanding of over 50% at 65 dB was possible in 7 patients at 12 months after the first fitting of CI.

CONCLUSIONS

Under certain conditions, CI was an effective solution to restore hearing in patients with SSD following translabyrinthine access to the skull base. Study with prospective design is required to provide more significant results.

Intraoperative acquisition of DTI in cranial neurosurgery: readout-segmented DTI versus standard single-shot DTI

OBJECTIVE

Diffusion tensor imaging (DTI) tractography is commonly used in neurosurgical practice but is largely limited to the preoperative setting. This is due primarily to image degradation caused by susceptibility artifact when conventional single-shot (SS) echo-planar imaging (EPI) DTI (SS-DTI) is acquired for open cranial, surgical position intraoperative DTI (iDTI). Readout-segmented (RS) EPI DTI (RS-DTI) has been reported to reduce such artifact but has not yet been evaluated in the intraoperative MRI (iMRI) environment. The authors evaluated the performance of RS versus SS EPI for DTI of the human brain in the iMRI setting.

METHODS

Pre- and intraoperative 3-T 3D T1-weighted and 2D multislice RS-iDTI (called RESOLVE [readout segmentation of long variable echo-trains] on the Siemens platform) and SS-iDTI images were acquired in 22 adult patients undergoing intraaxial iMRI resections for suspected low-grade glioma (14; 64%), high-grade glioma (7; 32%), or focal cortical dysplasia. Regional susceptibility artifact, anatomical deviation relative to T1-weighted imaging, and tractographic output for surgically relevant tracts were compared between iDTI sequences as well as the intraoperative tract shifts from preoperative DTI.

RESULTS

RS-iDTI resulted in qualitatively less regional susceptibility artifact (resection cavity, orbitofrontal and anterior temporal cortices) and mean anatomical deviation in regions most prone to susceptibility artifact (RS-iDTI 2.7 ± 0.2 vs SS-iDTI 7.5 ± 0.4 mm) compared to SS-iDTI. Although tract reconstruction success did not significantly differ by DTI method, susceptibility artifact-related tractography failure (of at least 1 surgically relevant tract) occurred for SS-iDTI in 8/22 (36%) patients, and in 5 of these 8 patients RS-iDTI permitted successful reconstruction. Among cases with successful tractography for both sequences, maximal intersequence differences were substantial (mean 9.5 ± 5.7 mm, range -27.1 to 18.7 mm).

CONCLUSIONS

RS EPI enables higher quality and more accurate DTI for surgically relevant tractography of major white matter tracts in intraoperative, open cranium neurosurgical applications at 3 T.

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.

[Postoperative imaging of the internal auditory canal : Visualization of active auditory implants. German version]

BACKGROUND

Assessment of the internal auditory canal (IAC) and the cochlea is of central importance in neurotology. The artefacts and visibility of the different types of active auditory implants in MRI vary, due to their specific ferromagnetic components. Knowledge of the size of MRI artefacts and the options for handling these is important for the auditory rehabilitation of specific diseases (e. g., vestibular schwannoma).

METHODS

The current paper is a literature review RESULTS: MRI assessment of the IAC and cochlea after surgical placement of an active auditory implant is feasible only with a percutaneous bone-anchored hearing aid (BAHA, Ponto). When specific factors (implant position and MRI sequence) are taken into consideration, these structures can be visualized even after cochlear implantation. Complications such as magnet dislocation and pain may occur.

CONCLUSION

The possibility of assessing the IAC and cochlea by MRI is an important aspect that needs to be taken into consideration when planning the auditory rehabilitation of patients after acoustic neuroma surgery.

MRI Metal Artifact Reduction Sequence for Auditory Implants: First Results with a Transcutaneous Bone Conduction Implant

Objective: Magnetic resonance imaging (MRI) is often limited in patients with auditory implants because of the presence of metallic components and magnets. The aim of this study was to evaluate the clinical usefulness of a customized MRI sequence for metal artifact suppression for patients with implants in the temporal bone region, specifically patients with a transcutaneous bone conduction implant. Methods: Two whole head specimens were unilaterally implanted with a transcutaneous bone conduction implant. MRI examinations with and without a primarily self-build sequence (SEMAC-VAT WARP) for metal artifact suppression were performed. The diagnostic usefulness of the acquired MRI scans was rated independently by two neuroradiologists. The sequence was also used to acquire postimplantation follow-up MRI in a patient with a transcutaneous bone conduction implant. Results: The customized SEMAC-VAT WARP sequence significantly improved the diagnostic usefulness of the postimplantation MRIs. The image acquisition time was 12 min and 20 s for the T1-weighted and 12 min and 12 s for the T2-weighted MRI. There was good agreement between the two blinded raters (Cohen’s κ = 0.61, p < 0.001). Conclusion: The sequence for metal artifact reduction optimized in Bern enables MRI at 1.5 T in patients with active transcutaneous bone conduction implants without sacrificing diagnostic imaging quality. Particularly on the implanted side, imaging of intracranial and supra- and infratentorial brain pathologies is clinically more valuable than standard diagnostic MRI without any artifact reduction sequences.

Postoperative imaging of the internal auditory canal : Visualization of active auditory implants

BACKGROUND

Assessment of the internal auditory canal (IAC) and cochlea is of central importance in neurotology. The artefacts and visibility of active auditory implants on magnetic resonance imaging (MRI) vary because of their specific magnetic components. Knowledge of the size of MRI artefacts and the options for handling them is important for the auditory rehabilitation of specific diseases (e. g., vestibular schwannoma).

METHODS

The current article is a literature review.

RESULTS

MRI assessment of the IAC and cochlea after surgical placement of an active auditory implant is feasible only with a percutaneous bone-anchored hearing aid (BAHA, Ponto). When specific factors (implant position and MRI sequence) are taken into consideration, these structures can be visualized even after cochlear implantation. Complications such as magnet dislocation and pain may occur.

CONCLUSION

The possibility of assessing the IAC and cochlea by MRI is an important aspect that needs to be taken into consideration when planning the auditory rehabilitation of patients after acoustic neuroma surgery.

Magnetic resonance imaging with cochlear implants and auditory brainstem implants: Are we truly practicing MRI safety?

OBJECTIVE

Our objective is to evaluate the safety in patients with cochlear implants (CIs) and auditory brainstem implants (ABI) undergoing 1.5 Tesla (T) magnetic resonance imaging (MRI). Secondly, we want to raise awareness on CI and MRI safety, and advocate for continued improvement and advancement to minimize morbidity for our CI patients.

METHODS

Retrospective case series from 2006 to 2018 at a single tertiary academic center. Data was collected on patients with CI or auditory brainstem implants undergoing MRI. Outcomes collected include demographic data, age at time of MRI, MRI characteristics, complications, CI manufacturer, and image quality.

RESULTS

Eighteen patients with CI or ABI collectively underwent a total of 62 MRI scans. Five of 15 (33%) CI patients with magnet had complications: five total of 24 MRI scans (21%). Two patients had magnet removal prior to 29 MRI scans without complications. Four of five MRI-related complications were equipped with a U.S. Food and Drug Administration-approved head wrap. Three of five required a trip to the operating room to explore and reposition the CI magnet; two could not complete MRI secondary to pain. Of the complications, two were Cochlear (Sydney, Australia), two Advanced Bionics (Valencia, CA), and one MED-EL (Innsbruck, Austria). Synchrony model (MED-EL) had 0 of seven complications, with a total of 19 MRI scans, which features a freely rotating and self-aligning magnet.

CONCLUSION

Our series offers a diverse number of CI manufacturers and is in accordance with other literature that CI MRI-related adverse events are occurring at an unacceptable frequency. We can promote CI MRI safety through our institutions' MRI CI patient protocols, raise awareness that diagnostic MRI benefits must outweigh CI-related complications, and advocate for continued industry technological innovation.

LEVEL OF EVIDENCE

4 Laryngoscope, 129:482-489, 2019.

Magnetic Resonance Imaging Artifacts and Cochlear Implant Positioning at 1.5 T In Vivo

Objective

Cerebral magnetic resonance imaging with the magnet of the cochlear implant receiver/stimulator in place causes artifacts and hinders evaluation of intracerebral structures. The aim of this study was to evaluate the internal auditory canal and the labyrinth in a 1.5T MRI with the magnet in place.

Study Design

Observational study.

Setting

Tertiary referral center.

Subjects and Methods

The receiver/stimulator unit was placed and fixed onto the head of three volunteers at three different angles to the nasion-outer ear canal (90°-160°) and at three different distances from the outer ear canal (5-9 cm). T1 and T2 weighted sequences were conducted for each position.

Results

Excellent visibility of the internal auditory canal and the labyrinth was seen in the T2 weighted sequences with 9 cm between the magnet and the outer ear canal at every nasion-outer ear canal angle. T1 sequences showed poorer visibility of the internal auditory canal and the labyrinth.

Conclusion

Aftercare and visibility of intracerebral structures after cochlear implantation is becoming more important as cochlear implant indications are widened worldwide. With a distance of at least 9 cm from the outer ear canal the artifact induced by the magnet allows evaluation of the labyrinth and the internal auditory canal.

Comparison of MRI in pediatric cochlear implant recipients with and without retained magnet

OBJECTIVE

To report and compare medical, radiological, and audiological outcomes in pediatric cochlear implant recipients who underwent 1.5 and 3 Tesla strength MRI with and without retained magnet.

METHODS

Retrospective chart review at a tertiary care pediatric hospital and review of literature. Patients were identified via electronic medical records database search and were included if they had MRI after cochlear implant.

RESULTS

Of twelve instances of MRI in pediatric cochlear implant recipients at our institution, two minor complications and one major complication were recorded. The rate of complication was equal between patients who underwent MRI with and without retained magnet. All minor complications resulted from MRI with retained magnet whereas the only major complication resulted from magnet removal. Two novel complications are reported, including: magnet removal resulting in silastic tear necessitating reimplantation and magnet dislocation with spontaneous reduction. Magnet removal significantly decreased the size of artifact, but did not alter the diagnostic utility of the MRI. While audiological measures varied chronologically from MRI scans, they did not appear to be appreciably altered by MRI.

CONCLUSION

MRI with and without magnet retention appear to carry risks of both major and minor complications. For the regions of interest for each scan, MRI quality was not appreciably altered by magnet status. Audiological measures appear unaffected by magnet status during MRI however, this may reflect natural variation.

Cranial MRI in a young child with cochlear implants after bilateral magnet removal

A young bilateral cochlear implant (CI) user required magnetic resonance imaging (MRI) to determine the cause of hydrocephalus. The images obtained with the CIs in place were not diagnostically useful due to large artefacts generated by the CI magnets. We obtained useful images by bilaterally explanting the CI-magnets and replacing them with non-magnetic placeholder dummies then conducted the imaging. The artefact in the new images was greatly reduced and the images were diagnostically useful. Lastly, we explanted the dummies and reimplanted the CI-magnets. This procedure should be useful to obtain useful images in CI users.

Sonographic diagnosis of acute mastoiditis and subsequent retroauricular abscess in a pediatric cochlear implant recipient: A case report

When acute mastoiditis occurs in cochlear implant recipients, it can progress to subsequent retroauricular abscess due to the absence of the external mastoid cortex resulting from mastoidectomy performed for cochlear implantation. The management goal is to control infection while preserving the implanted device. A 2-year-old boy with cochlear implants developed acute mastoiditis and a subsequent retroauricular abscess. The patient underwent a surgical intervention based on the diagnosis made utilizing gray-scale and power Doppler sonography. This case illustrates the diagnostic usefulness of sonography in this rare situation. © 2017 Wiley Periodicals, Inc. J Clin Ultrasound 45:515-519, 2017.