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.

Cochlear implants and 1.5 T MRI scans: the effect of diametrically bipolar magnets and screw fixation on pain.

BACKGROUND: The probability that a patient will need an MRI scan at least once in a lifetime is high. However, MRI scanning in cochlear implantees is associated with side effects. Moreover, MRI scan-related artifacts, dislodging magnets, and pain are often the most frequent complications. The aim of this study was to evaluate the occurrence of pain in patients with cochlear implant systems using 1.5T MRI scans. METHODS: In a prospective case study of 10 implantees, an MRI scan was performed and the degree of pain was evaluated by a visual analog scale. Scans were performed firstly with and depending on the degree of discomfort/pain, without a headband. Four of the cochlear implants contained a screw fixation. Six cochlear implants contained an internal diametrically bipolar magnet. MRI observations were performed with a 1.5 T scanner. RESULTS: MRI scans were performed on all patients without causing any degree of pain, even without the use of a headband. CONCLUSION: Patients undergoing 1.5 T MRIs with devices including a diametrically bipolar magnet or a rigid implant screw fixation, experienced no pain, even without headbands.

Evaluation of Cochlear Implant Receiver Position and Its Temporal Changes.

HYPOTHESIS: It was the aim of this study to establish normative data regarding intended changes in cochlear implants (CI) receiver positioning by one surgeon over time. BACKGROUND: With the increasing number of CI patients, the probability of needing magnetic resonance imaging (MRI) increases. The accessibility of cerebral structures is limited by MRI artifacts caused by CI. New studies show a dependence of the visibility of intracranial structures by the MRI sequences and the position of the CI receiver itself. METHODS: Retrospective and interindividual investigation of topograms with regard to the nasion-external auditory canal-internal magnet angle and the distance between the internal magnet and the external auditory canal. We evaluated scans of 150 CI recipients implanted from 2008 until 2015. RESULTS: The most common implant position in the years 2008 to 2015 was a nasion-external auditory canal-internal magnet angle between 121 and 140 degrees (mean, 127 degrees) and an internal magnet-external auditory canal distance between 61 and 80 mm (mean, 70 mm). Over time the nasion-external auditory canal-internal magnet angle increased and the internal magnet-external auditory canal distance decreased, both to a statistically significant degree. A difference between the manufacturers was not observed. CONCLUSION: The CI receiver position is important for an artifact-free examination of the internal auditory canal and the cochlea. The realization of the position over a time course supports awareness of artifact-related visibility limitations.