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

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          Abstract

          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.

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          Most cited references 27

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          Magnetic resonance imaging at 1.5 T after cochlear implantation.

          To assess the safety of 1.5 T magnetic resonance imaging (MRI) in patients with cochlear implants (CIs) with internal magnets. Retrospective review of CI patients who underwent an MRI at Johns Hopkins. Sixteen patients with a mean age of 43 ± 22 years with a CI underwent a total of 22 clinically indicated 1.5 T MRI. Devices from 3 major CI manufactures were represented. Binding of CI with mold material and gauze was performed before MRI. Some patients were also administered a sedative. Intravenous gadolinium contrast was used in all but 1 patient. Patients were assessed with regard to the ability to complete the MRI, the size of the artifact caused by the device, the ability to make a diagnosis from the studies, the post-MRI CI function, and the magnet's position. No CI malfunction, displacement, or magnet displacement was observed after MRI. One patient was unable to tolerate the procedure because of pressure at the site of the device. One patient required intravenous sedation to complete the study. The CI generally produced an artifact on brain MRI, with a mean maximal anterior-posterior dimension of 6.6 cm and a lateral dimension of 4.8 cm around the site of the device. The contralateral internal auditory canal was visualized in all patients, and the ipsilateral internal auditory canal was at least party visible in all but 1 patient. Patients can safely undergo 1.5 T MRI after CI if the device is tightly bound before scanning. Magnet displacement was not observed, and we think the risk to be minimal compared with the risk and inconvenience of removing the magnet before the study.
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            Imaging of intralabyrinthine schwannomas: a retrospective study of 52 cases with emphasis on lesion growth.

            Only a few case reports and small series of intralabyrinthine schwannomas (ILSs) have been reported. The purpose of this study was to assess prevalence, MR characteristics, location, clinical management, and growth potential/patterns of ILSs in the largest series reported. Lesion localization, MR characteristics, lesion growth, and clinical management were reviewed in 52 patients diagnosed with an ILS between February 1991 and August 2007 in 2 referral centers. The number of ILSs and vestibulocochlear schwannomas in the cerebellopontine angle/internal auditory canal was compared to assess the prevalence. ILSs most frequently originate intracochlearly, are hyperintense on unenhanced T1-weighted images, enhance strongly after gadolinium administration, and are sharply circumscribed and hypointense on thin heavily T2-weighted 3D images. The scala tympani is more frequently or more extensively involved than the scala vestibuli. Follow-up MR imaging, available in 27 patients, showed growth in 59% of subjects. Growth was seen from the scala tympani into the scala vestibuli and from the scala vestibuli to the saccule and vice versa. Twelve lesions were resected, and the diagnosis of ILS histopathologically confirmed. ILSs can account for up to 10% of all vestibulocochlear schwannomas in centers specializing in temporal bone imaging, grow in more than 50%, and are most frequently found intracochlearly, often anteriorly between the basal and second turn. Cochlear ILSs most often originate in the scala tympani and only later grow into the scala vestibuli. Growth can occur from the cochlea into the vestibule or vice versa through the anatomic open connection between the perilymphatic spaces in the scala vestibuli and around the saccule.
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              Cochlear implant magnet displacement during magnetic resonance imaging.

              Magnet displacement is a rare but possible complication in patients with cochlear implants. We report 1 case in a young child that occurred during magnetic resonance imaging scanning, despite precautionary measures taken by the surgeon and the radiographer. Retrospective case report. This case is presented by the ENT Department of Armand Trousseau Paediatrics Hospital, Paris, France. An 8-year-old child, implanted with a Freedom Contour Nucleus cochlear implant, was referred for a 1.5-T cerebral magnetic resonance imaging because of a progressive neurologic disorder. This rare complication underlines the importance of risk information and preventive measures required, even in case of compatible devices, for performing a magnetic resonance imaging examination in patients wearing a cochlear implant with removable magnet.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                22 July 2015
                2015
                : 10
                : 7
                Affiliations
                [1 ]University Department of Diagnostic and Interventional Neuroradiology, Inselspital Bern, Bern, Switzerland
                [2 ]University Department of Otorhinolaryngology, Head & Neck Surgery, Inselspital Bern, Bern, Switzerland
                [3 ]ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
                University of North Carolina at Chapel Hill, UNITED STATES
                Author notes

                Competing Interests: The authors of this manuscript declare that they thank the MEDEL Corporation [MED-EL Corporation, Innsbruck, Austria] for loan of the cochlear implants and funding that study [total amount 15 000€]. The authors state that this work has received funding from MED-EL Corporation [MED-EL Corporation, Innsbruck, Austria] in the amount of 15 000€. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials.

                Conceived and designed the experiments: FW MDC. Performed the experiments: FW LL WW. Analyzed the data: FW LL. Contributed reagents/materials/analysis tools: FW WW LL SW MV RW GM MDC. Wrote the paper: FW.

                Article
                PONE-D-15-13603
                10.1371/journal.pone.0132483
                4511764
                26200775
                bdc8c507-afc2-4892-9e2f-27840ac0b0f3

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

                Page count
                Figures: 5, Tables: 5, Pages: 17
                Product
                Funding
                The authors of this manuscript declare that they thank the MEDEL Corporation [MED-EL Corporation, Innsbruck, Austria] for loan of the cochlear implants and funding that study [total amount 15 000€]. The authors state that this work has received funding from MED-EL Corporation [MED-EL Corporation, Innsbruck, Austria] in the amount of 15 000€. Additionally, the authors confirm that the funders had no role in our study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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