Significant Artifact Reduction at 1.5T and 3T MRI by the Use of a Cochlear Implant with Removable Magnet: An Experimental Human Cadaver Study
Significant Artifact Reduction at 1.5T and 3T MRI by the Use of a Cochlear Implant with Removable Magnet: An Experimental Human Cadaver Study
Franca Wagner 0 1
Wilhelm Wimmer 0 1
Lars Leidolt 0 1
Mattheus Vischer 0 1
Stefan Weder 0 1
Roland Wiest 0 1
Georgios Mantokoudis 0 1
Marco D. Caversaccio 0 1
0 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
1 Editor: Sompop Bencharit, University of North Carolina at Chapel Hill, UNITED STATES
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
with a removable magnet.
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
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.
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.
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.
collection and analysis, decision to publish, or
preparation of the manuscript.
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
Cochlear implants (CIs) have become a highly standardized and safe treatment for hearing
restoration in prelingually deafened children and postlingually deafened children or adults.
The indications for CI implantations are constantly expanding. Patients receiving a CI might
have three major disadvantages regarding magnetic resonance (MR) imaging: 1) the magnetic
receiver coil under the skin might cause pain during the acquisition of the MR images, 2)
dislocation of the implant is possible, and 3) the internal magnet creates large artifacts that limit the
diagnostic validity. MR imaging (MRI) is often required for brain, head and neck examinations
for a prolonged period following CI implantation. One study predicted that the lifetime
prevalence of neurological disorders requiring brain MR imaging in patients with CI implants is 6.25
percent , so this issue affects a very large number of patients. About 10% of cochlear carriers
in developed countries can be expected to undergo MRI within their lifetimes .
The indication for CI expanded from single-sided implantation to bilateral implants, and
from elderly patients with single-sided deafness to those with residual hearing. For many years
patients with CI could not undergo MRI examinations. However in the last 15 years, several
studies by different research teams and manufacturers have shown no major incidents in MRI
examinations using field strengths up to 1.5T. This was first evaluated with in vitro studies [3–
7], then in cadaveric studies or in studies involving only a few patients [8–11], followed by
studies involving larger numbers of patients [12–15]. Finally, several authors concluded that
MRI scans up to 1.5T are safe in patients carrying CIs with non-removable magnets if strict
guidelines are followed [16–18]. With the continuing trend towards higher field strength MRI,
the compatibility of CIs with 3T MRI is important.
MR imaging in CI patients also raises concerns regarding MRI-induced artifacts caused by
the implant [14,16,19,20]. A CI includes a removable external speech processor and transmitter
coupled transcutaneously to a surgically implanted component. A small internal CI magnet is
used to magnetically hold the external part (audio processor coil) safely over the implant,
which guarantees sufficient transmission quality between the external transmitter and the
internal receiver . Artifacts are induced by both the metallic parts of the CI and the magnet
inside the implant. Therefore many physicians consider this a contraindication to MRI,
especially in units operating at high-field strength [14,16,19,20]. Thus, the artifacts caused by CIs in
brain MR imaging remain a concern.
One solution to reduce artifacts and to increase patient safety was proposed by the
company MED-EL (MED-EL Corporation, Innsbruck, Austria), which is developing implants
with removable magnets. MED-EL implants have long been CE (Conformité
Européenne)approved for MRI at field-strengths of 0.2T, 1.0T and 1.5T [5,6,12,14,20]. For countries
accepting the CE mark and FDA approval, the Mi1200 SYNCHRONY CI (Fig 1) is CE-approved and
labeled as MR conditional for MRI at magnetic field strengths of 0.2T, 1.0T, 1.5T and 3T, and
labeled as MR conditional for examinations at 1.5T and 3T magnetic field strengths. This is
due to a design that allows the implant magnet to freely rotate and self-align within its silastic
housing, reducing implant torque and the risk of demagnetization during MR scans. The
implant also offers the possibility of removing the magnet in case of large imaging artifact
Other cochlear implant manufacturers also offer devices that enable scanning procedures at
3T. Cochlear (Sydney, Australia) offers a 3T-approved device with the possibility of magnet
removal to decrease MRI-related artifacts. A similar product is offered by Advanced Bionics
(Stäfa, Switzerland), which has approval for up to 1.5T. Neurelec’s device (Oticon Medical,
Askim, Sweden) is approved for up to 1.5T in a ceramic housing, even with a non-removable
Fig 1. The MED-EL Mi1200 SYNCHRONY Cochlear Implant (MED-EL, Innsbruck, Austria). The MED-EL Mi1200 SYNCHRONY Cochlear Implant
(MED-EL, Innsbruck, Austria) is compatible with MRI at a magnetic-field strength of up to 3T and with the possibility of removing the internal magnet (1a). The
magnet is freely rotating (1b). In Fig 1C the magnet is in a random position, when no external magnetic field is applied and in contrast in Fig 1D the
magnet aligned parallel to the external magnetic field.
The primary aim of this human cadaveric study was to determine to what extent MR brain
artifacts are reduced after explantation of the removable magnet of the MED-EL Mi1200
SYNCHRONY cochlear implant at 1.5T and at 3T with different MR sequences. Secondary
objectives were to determine to what extent the magnet in situ affects the diagnostic usefulness and
image quality at 1.5T and at 3T.
Materials and Methods
This experimental study was designed and conducted according to the guidelines of the
Cantonal Ethics Committee and the Cantonal Animal Experimentation Commission of Bern.
Our institutional review board–the Head Office Education and Research–approved this study
The Institute of Anatomy, University of Bern, Switzerland (http://www.ana.unibe.ch)
received written informed consent from all donors. This is a legal requirement and serves as
liable document to justify any donation and to further guarantee that the act of donation meets
all legal requirements. Furthermore, the written consent allowed us to use human body parts
for research with human material according to Swiss jurisdiction. The specimens used in this
study have not been used or described in previous publications.
Anatomical specimens and surgical procedure
In order to accurately simulate an MR brain examination for evaluating intracranial pathology
in a human, the CI was implanted in five Thiel-fixed  cadaver heads. The Thiel
conservation technique is considered to realistically replicate the color, mobility and flexibility of tissues
in intraoperative situations and to offer excellent conditions for the training of surgical
procedures in otology . In contrast to the frequently used formaldehyde fixation for anatomic
specimens, the Thiel solutions are adapted to individual organ systems. Structure and
consistency of the tissues of the auditory canal, the tympanic cavity and the mastoid are comparable
to vital conditions . This enabled a surgical preparation under conditions close to the
The five cadaver heads were obtained from the Institute of Anatomy, University of Bern.
First, in all five cadavers a native 1.5T and 3T baseline MR imaging was performed to verify
sufficient conservation of the anatomical structures and to exclude any other lesions (e.g.
tumors, large hemorrhage or advanced putrefaction) that might affect the study. To avoid
accumulation of air bubbles in the heads, especially in parieto-occipital spaces and in the
cerebellopontine angle, the heads were placed according to the normal supine position of a human
head in MR for 48 hours before the MR examination. With this positioning the post-mortem
intracranial air accumulated in the frontal lobes and the frontal subarachnoidal space.
All imaging studies were performed using 1.5T and 3T Siemens scanners (Magnetom
Avanto, Magnetom Verio, respectively; Siemens Medical Solution, Erlangen, Germany) with
12-channel head coils. Our pre-implantation MRI protocol included T1-weighted (w)
multiplanar (MPR) sequences, axial T1w and T2w sequences, a coronal T2w, an axial fat suppressed
T1w, and an axial constructive interference in steady state (CISS), in accordance with our
native temporal bone MR protocol. The corpse heads were supine positioned in the MR
scanners according to the standard position in routine clinical practice.
Imaging study protocol
First, all five corpse heads were scanned without the cochlear implant at 1.5T and 3T. Then the
MR scanning was repeated with the entire implant and magnet in place. Finally the five corpse
heads were MR scanned after explantation of the removable magnet. The MR study protocol at
1.5T and 3T for the non-implanted, implanted with magnet in situ, and implanted without
magnet corpse heads was exactly the same. The chosen MR examination protocol corresponds
exactly to our institutional protocol for the assessment of pathologies in the cerebellopontine
angle and temporal bone without contrast application.
For the 1.5T MR scanner the following parameters were used: T1w multiplanar (MPR):
repetition time (TR) 1830 ms, echo time (TE) 2.92 ms, slice thickness 1.0 mm and field of view
(FoV) 256x256 mm2; acquisition time: 5 minutes (min) and 30 seconds (sec). Axial T1w:
TR490 ms, TE 8.4 ms, slice thickness 5.0 mm and FoV 192x220 mm2; acquisition time: 2:13
min. Axial T2w: TR 4100 ms, TE 100 ms, slice thickness 5.0 mm and FoV 191x219 mm2;
acquisition time: 1:51 min. Coronal T2w: TR 3500 ms, TE 98 ms, slice thickness 2.0 mm and FoV
180x180 mm2; acquisition time: 3:13 min. Axial T1w (fat suppression): TR 492 ms, TE 11 ms,
slice thickness 2.0 mm and FoV 190x190 mm2; acquisition time: 1:34 min. CISS: TR 1200 ms,
TE 264 ms, slice thickness 0.6 mm, FoV 200x200 mm2 and a flip angle 150°; acquisition time:
Analogous to the 1.5T sequences, the 3T MRI sequences were implemented with the
following parameters: T1w MPR: TR 2530 ms, TE 2.2 ms, slice thickness 1.0 mm and FoV 256x256
mm2; acquisition time: 3:58 min. Axial T1w: TR 250 ms, TE 3 ms, slice thickness 5.0 mm and
FoV 192x220 mm2; acquisition time: 2:14 min. Axial T2w: TR 5270 ms, TE 86 ms, slice
thickness 5.0 mm and FoV 192x220 mm2; acquisition time: 1:26 min. Coronal T2w: TR 4000 ms,
TE 93 ms, slice thickness 3.0 mm and FoV 181x200 mm2; acquisition time: 3:14 min. Axial
T1w (fat suppression): TR 319 ms, TE 8.6 ms, slice thickness 3.0 mm and FoV 198x220 mm ;
acquisition time: 2:22 min. CISS: TR 1000 ms, TE 132 ms, slice thickness 0.5 mm, FoV
199x199 mm2 and a flip angle of 120°; acquisition time: 6:32 min.
Surgical procedure for implant removal
A conventional transmastoid posterior tympanotomy approach was performed by five
experienced otologists (GM, MV, SW and MDC). A bone bed for the CI body and a bony channel for
the electrode cable were prepared behind the ear. The CI implant bodies were additionally
fixed using resorbable sutures (Vicryl 2.0). The round window membrane was exposed by
removal of the bony overhang and the electrode arrays were inserted through the round
window into the cochlea. All electrode arrays were fully inserted without complications. Finally, a
double-layered wound closure was performed. Three of the five corpse heads were implanted
on the left side and the other two were implanted on the right. After the MR scans with the
magnet in situ the magnet was explanted using a dedicated magnet removal tool via a small
skin incision of 180 degrees around the receiver coil. One of the otologists did the incision for
magnet exchange behind the ear beside the implant in all cases. After removal of the magnet a
non-magnetic spacer (titanium shell without a magnet inside) was inserted as a placeholder
with a dedicated insertion tool. The configuration of the implant with the non-magnetic spacer
is hereafter referred to as “implant without magnet”.
Evaluation of the images was performed by two experienced neuroradiologists (FW and LL),
who reviewed the MR images independently. The acquired MR images were rated on certified
reporting stations (DIN V 6868–57 and QA guideline). Three criteria–diagnostic usefulness,
artifacts, and image quality–were defined and assessed on scales of 1 to 4 (Table 1). The
following brain structures were evaluated and graded on the ipsilateral CI side with regard to the
three defined criteria: temporal, parietal and occipital lobe; cerebellum (vermis, lobus cranialis
cerebelli and pedunculus cerebellaris medius); cerebellopontine angle with internal auditory
canal; membranous labyrinth (cochlea, vestibulum and semicircular canals); and the brain
1 completely unusable
The presentation order of the MR images was in line with the mentioned acquisition: T1w
MPR, axial T1w, axial T2w, coronal T2w, axial T1w with fat suppression, and CISS. The
window values (picture contrast and brightness) could be adjusted by the examiner.
Diagnostic usefulness focused on the clinical detection, verification, and staging of possible
brain pathology. The value was assessed using a 4-point ordinal rating scale: 4 = best picture
quality; 3 = diagnostic image quality (assessable); 2 = inadequate; and 1 = completely unusable.
Extent of artifacts was evaluated using a 4-point ordinal rating scale: 4 = no artifacts visible;
3 = artifacts present but do not impair assessment of the anatomic structures; 2 = strong
artifacts with limited evaluation of the anatomic structures; 1 = very distinct artifacts that prevent
evaluation of the anatomic structures.
Image quality was defined as how accurately the MR images could represent an intracranial
pathology; this was based on the brightness and evenness of illumination, contrast, and
resolution of the observed images. Evaluation of the image quality was based on the raters’ entire
image impression, with special regard to the detection, verification, and staging of possible
brain pathology. This also used a 4-point rating scale: 4 = best, 3 = good, 2 = insufficient, and
1 = completely deficient image quality.
In order to determine significant differences in the three rated criteria between the MR images
acquired with or without presence of the magnet, we used the one-sided sign test for the
statistical analysis due to the small number of cadaver heads. The inter-rater-agreement between the
two blinded raters (FW and LL) was tested with the Cohen’s Kappa. A p-value < 0.05 was
considered statistically significant.
For 1.5T and 3T, the MR images with the magnet in situ showed very distinctive artifacts
consisting of a circular round signal void with an average maximal diameter of 5 cm (Figs 2 and 3)
and a standard deviation (SD) of +/-1.5 cm, depending on the MR sequence. Particularly in the
T1 MPR sequences and the CISS, pronounced shadowing artifacts were visible and covered the
hemisphere and the cerebellum ipsilateral to the CI. Adjacent to the signal void, geometric
distortions and reduced signal intensity were noted up to 8 cm (SD +/- 2cm) away from the center
of the implant, which was also dependent on the MR sequence (T1 MPR and CISS). Overall,
the acquired MR images with the magnet in situ were unusable for review of anatomical
supraand infratentorial brain structures or for clinical diagnosis on the implant side (inter-rater-
reliability = 1, Table 2). On the contralateral (non-implanted) side the supra- and infratentorial
brain structures were not layered by artifacts at 1.5T and 3T, and were considered to have best
image quality and best picture quality for diagnostic usefulness (inter-rater-agreement = 1).
After removal of the magnet the quality of the obtained images at 1.5T and 3T improved
significantly, with small (maximum diameter 1.0 cm on 1.5T and 1.5 cm on 3T (SD
+/0.5 cm)) residual artifacts on the implanted side. These residual artifacts masked the peripheral
lateral parietal and occipital lobes, the parietal and occipital bone, the parietal and occipital
Fig 2. MR image series of one corpse head at 1.5T with magnet in situ. 2a: T1w MPR sagittal; 2b: T1w
axial; 2c: T2w axial; 2d: T2w coronal;2e: CISS. The MR images show the maximum in diameter of the artefact
in each sequence.
subcutaneous tissue and the lateral cranial lobus cranialis cerebellaris (Table 2). This situation
was comparable to the MR scans with magnet in situ, which also showed stronger artifacts on
the T1 MPR and CISS.
The occipital lobe, the vermis and pedunculus cerebellaris medius, the cerebellopontine
angle with internal auditory canal, the membranous labyrinth (including cochlea, vestibulum
and semicircular canals), and the brain stem were free of signal voids (Figs 4 and 5, Table 2).
In summary, the MR images after magnet removal at 1.5T and 3T enabled good image
quality and diagnostic usefulness for the clinical practice and the evaluation of brain pathologies in
CI carriers on the implanted side (Table 2). For the assessment of intracranial pathologies on
the non-implanted side, a diagnostic-quality image is achievable at 1.5T and 3T even with the
magnet in situ.
With the magnet in situ and a field strength of 1.5T, three of the five acquired image series of
the corpse heads were inadequate (rated with 2) and the other two were completely unusable
(rated with 1). After magnet removal all five image scans were diagnostic useful (rated with 3).
With the magnet in situ and a field strength of 3T, all images of the five cadavers were
completely unusable (grade 1). After magnet removal both raters labeled the five image series
with 3 (diagnostic image quality). The results are summarized in Table 3.
Improvement of the diagnostic usefulness after magnet removal at 1.5T and 3T was
statistically significant (p-value 0.03), with no statistical difference between the different magnetic
All five of the assessed images at 1.5T and 3T with the CI magnet in situ had artifacts that
affected the assessment of the anatomic structures. At 1.5T, 4 out of 5 images had strong
artifacts with limited evaluation of the anatomic structures (grade 2); one image had very
distinctive artifacts that prevented evaluation of the anatomic structures (grade 1). After removal
of the magnet (i.e. exchange by the non-magnetic spacer) all images at 1.5T were graded 3
(artifacts present; no impaired assessment of the anatomic structures) by both reviewers.
At 3T all five MR scans with the magnet in situ had very distinctive artifacts that interfered
with the evaluation of the anatomic structures (grade 1). After magnet removal the five MR
image series were all scored 3 (artifacts present; no impaired assessment of the anatomic
structures). The results are summarized in Table 4. The artifact reduction was statistically
significant, with a p-value of 0.03 after the explantation of the magnet on 1.5T and 3T MR, with no
difference between the two field strengths.
With the magnet in situ and a field strength of 1.5T, three of the five cadavers showed
insufficient image quality (grade 2) and two had completely deficient image quality (grade 1). After
explantation of the magnet, the image series of all corpse heads were rated grade 3 (good image
quality). The quality ratings for the 3T scans before the magnet removal were consistent for all
five cadaver heads graded 1 (completely deficient image quality). At 3T without magnet the
Fig 3. MR image series of one corpse head at 3T with magnet in situ. 3a: T1w MPR sagittal; 3b: T1w
axial; 3c: T2w axial; 3d: T2w coronal; 3e: CISS. The MR images show the maximum in diameter of the
artefact in each sequence.
five acquired MR image series were rated as grade 3 (good image quality). The results are
summarized in Table 5. A statistically significant difference was shown between the quality of the
acquired images at 1.5T and 3T before and after the magnet removal (p-value 0.03). There was
no statistical difference between the rating results after magnet removal at 1.5T and 3T.
The inter-rater-reliability was 1 for the three analyzed criteria–diagnostic usefulness,
artifacts and image quality–after the magnet removal for the scans at 1.5T and 3T.
The MR images after magnet removal at 1.5T and 3T enabled the expected good image quality
and diagnostic usefulness for the clinical practice and the evaluation of brain pathologies on
the implanted side in CI carriers. The overall artifacts caused by the magnet in situ—more
pronounced at 3T than at 1.5T —were significantly reduced after magnet removal at both field
strengths. The acquired sequences at 1.5T and 3T after the magnet explantation indicated good
visualization of the normal supra- and infratentorial brain structures without distortion. For
assessment of intracranial pathologies on the non-implanted side, a diagnostic image quality is
achievable even with the magnet in situ at 1.5T and 3T.
While aspects of CI magnet movements with potential CI damage or harm to the patients
during or after MR scans are discussed elsewhere , the present human cadaver study
analyzed diagnostic usefulness, artifacts and image quality of acquired MR brain series after
cochlear implantation before and after magnet removal using a 1.5T and a 3T MR scanner. A
previous report documented that CI devices with internal magnet removal are safe for 1.5T
MR systems . If the patient needs more than one MR examination the explanted magnet
can be replaced with a titanium spacer and a new magnet can be placed when the patient has
obtained all necessary MRIs [24,25,26].
This study confirmed previous results that image quality was significantly reduced on the
implanted side by in situ magnet artifacts at both 1.5T and 3T, resulting in deficient image
quality that was unusable for evaluating brain parenchyma, anatomy or underlying pathologies
on the side of implant. Therefore, removal of the magnet for MR imaging of the brain, head, or
Anatomical structure implanted side
1.5T MR magnet in situ
1.5T MR without magnet
3T MR magnet in situ
3T MR without magnet
Fig 4. MR series of corpse head at 1.5T after magnet removal with non-magnetic spacer in situ. 4a:
T1w MPR sagittal; 4b: T1w axial; 4c: T2w axial; 4d: T2w coronal; 4e: CISS.
neck region might be justified for initial or baseline imaging. In follow-up studies with known
localization of the intracranial pathology (e.g. postoperative scans, benign brain tumors, low
grade gliomas or demyelinating CNS disease) it might be not necessary to remove the magnet
if the lesion is not in the previously documented area of cancellation artifact. This is an
important fact especially for patients with neurofibromatosis type 2 who are offered cochlear
implantation as standard treatment in the presence of an intact cochlear nerve and stable vestibular
schwannomas . Neurofibromatosis type 2 patients are required to have regular MR
scanning to monitor disease progression, and, as a result, the safety and efficacy of repeated
scanning can be improved by removal of the magnet.
Although magnet removal can be easily performed under local anesthesia via a small incision
behind the ear, it may lead to additional costs and inconvenience for the patient. After
completion of the MR scan the magnet can be repositioned manually with the magnetic insertion tool.
The procedures to remove and to re-insert the magnet take about 15 minutes, from application
of local anesthesia until the final sterile wound dressing. To avoid potential excessive scarring
and adhesions that may occur after this minor procedure, the MED-EL Mi1200 SYNCHRONY
cochlear implant includes a protective coating to prevent unwanted cellular adhesions. It is
important to note that long-term study results concerning cellular adhesions in humans are not
yet available. Furthermore, in vivo, infectious agents might spread along the incision into the
cochlea, thus paving the way for intracranial infections such as meningitis. However, this
potential complication should be avoidable in a sterile setting for magnet removal and re-implantation.
Although we did not measure the temperature of the samples at the end of the MR examination,
in our opinion the effect is inconsequential, as confirmed in prior studies .
Moreover, explantation of the magnet might result in weakening of the silicone pocket and
thus increase the risk for a recurrence of dislocation [28,29]; however no long-term studies
have been reported and the cited references refer to implant designs with removable magnets
that are fundamentally different from the removable magnet design in the current study. The
conical design of the MED-EL magnet is designed to avoid weakening of the silicone pocket.
Demagnetization of the magnet is described in the literature as a potential problem that
depends on the position of the magnet in relation to the magnetic field of the scanner . The
magnet of the Synchrony implant is freely rotating and aligned parallel to the external magnetic
field (Fig 1), thereby avoiding this problem.
Additionally, we are aware that some MR sequences are more exposed to cochlear implant
magnet-induced field distortions and consequent more pronounced artifacts. The chosen MR
examination protocol corresponds exactly to our institutional protocol for the assessment of pathologies in
the cerebellopontine angle and temporal bone without contrast application. This closely simulates
the methods used for neuroradiologic staging of patients with otovestibular complaints of unknown
origin, sensorineural hearing loss, or for diagnostic and follow up of an intracochlear schwannoma;
see, for example the case descriptions of Bittencourt at al.  and Tieleman et al. .
The chosen MR protocol is, in our opinion, consistent with standard ENT baseline imaging
for temporal bone and internal auditory canal pathologies. This protocol is essential in the
work-up of tumors and inflammatory diseases, such as the previously mentioned
schwannomas, epidermoids, cholesterol granulomas, paragangliomas and transtegmental masses.
In accordance with the recently published work of Todt et al  we noticed that the
artifacts are highly dependent on the technical scanning MR sequences used. In particular, the 3D
CISS and the T1w MPR enlarge artifacts. But after magnet removal both sequences are suitable
1.5T MR without magnet
Fig 5. MR series of corpse head at 3T after magnet removal with non-magnetic spacer in situ. 5a: T1w
MPR sagittal; 5b: T1w axial; 5c: T2w axial; 5d: T2w coronal; 5e: CISS. The MR images show the maximum
diameter of the artefact in each sequence.
to evaluate pathologies of the cerebellopontine angle and to exclude, for example, the
reoccurrence of a vestibular schwannoma within the inner ear or the internal auditory canal. An
intralabyrinthine hemorrhage may also be solely depicted by unenhancend T1w MPR . The 3D
CISS is a standard part of a complete posterior fossa and internal auditory canal protocol, and
is a mainstay for imaging of the cisternal cranial nerves at the cerebellopontine angle and
internal auditory canal .
Todt et al.  also recommend a more horizontal and posterior position of the magnet for
evaluation of the internal auditory canal and the labyrinth. In our opinion this is worth
discussion because the authors focused exclusively on the ipsilateral infratentorial internal auditory
canal and inner ear structures. We showed in our study that even with a standard
retroauricular localization (nasion-ear angle) of the implant, an evaluation of the inner ear structures on
the implanted side is possible after removal of the magnet. In consequence, the ipsilateral
supratentorial brain structures must be more affected by artifacts due to the more horizontal
and posterior implant position. Unfortunately, Todt et al.  do not discuss this issue.
Additionally, the authors described the magnet dislocation at 3T as a yet unsolved problem .
Cochlear implants with a free rotating magnet aligning parallel to the external magnetic field
solves this problem, and also solves the potential problem of magnet demagnetization.
In our opinion the removal of the magnet is a good method to reduce the artifacts,
independent of the MR field strength, and to significantly avoid restrictions on the possible diagnosis
of cerebral pathologies, including pathologies that are outside the area of the internal auditory
canal and the inner ear structures of the implanted side. Besides the MR indication there is no
other reason for a magnet removal; from the perspective of a CI carrier, magnet removal is
disadvantageous in all conditions except MR scanning.
Our study is limited by the small sample size. We tested only the MED-EL Mi1200
SYNCHRONY cochlear implant system. Our results cannot be generalized to the other implant
types such as Cochlear (Sydney, Australia), Advanced Bionics (Stäfa, Switzerland) and
Neurelec’s device (Oticon Medical, Askim, Sweden).
Our small cadaver cohort showed, however, a good diagnostic value and good MR image
quality with minimal artifacts on the implanted side at 1.5T and 3T after magnet removal.
In conclusion, MR brain, head, and neck imaging can be performed in cochlear implant
carriers at 1.5T and 3T without sacrificing diagnostic imaging quality, provided that the free
rotating magnet is removed. On the implanted side, images of intracranial supra- and infratentorial
brain pathologies are clinically more valuable after magnet removal as compared to diagnostic
MR imaging with the magnet in situ. Removal of the magnet is advised for initial or baseline
imaging. We recommend preserving the magnet in situ in patients with a known intracranial
pathology outside of the artifact area.
The authors thank the MED-EL Corporation for loan of the cochlear implants.
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.
1. MacDonald BK , Cockerell OC , Sander JW , Shorvon SD . The incidence and lifetime prevalence of neurological disorders in a prospective community-based study in the UK . Brain. 2000 ; 123 : 665 - 676 . PMID: 10733998
2. Wagner J , Rademacher G , Mutze S , Mittmann P , Ernst A , Todt I. MRI artifacts caused by hearing implants: assessment of the internal auditory canal in cochlear implant users . Presented at the 13th International Conference on Cochlear Implants and Other Implantable Auditory Technologies 2014 ; P2-2-26 . Available: http://epub.ub.uni-muenchen.de/ 20931 /1/CI2014_Book_of_Abstracts.pdf. Accessed 2015 Jun 9.
3. Chou CK , McDougall JA , Can KW . Absence of radiofrequency heating from auditory implants during magnetic resonance imaging . Bioelectromagnetics . 1995 ; 16 : 307 - 316 . PMID: 8554632
4. Heller JW , Brackmann DE , Tucci DL , Nyenhuis JA , Chou CK . Evaluation of MRI compatibility of the modified nucleus multichannel auditory brainstem and cochlear implants . Am J Otol . 1996 ; 17 : 724 - 729 . PMID: 8892568
5. Teissl C , Kremser C , Hochmair ES , Hochmair-Desoyer IJ . Cochlear implants: in vitro investigation of electromagnetic interference at MR imaging: compatibility and safety aspects . Radiology . 1998 ; 208 : 700 - 708 . PMID: 9722849
6. Teissl C , Kremser C , Hochmair ES , Hochmair-Desoyer IJ . Magnetic resonance imaging and cochlear implants: compatibility and safety aspects . J Magn Reson Imaging . 1999 ; 9 : 26 - 38 . PMID: 10030647
7. Vincent C , Ruzza I , Vaneecloo FM , Dubrulle F. Magnetic resonance imaging with the Digisonic SP Neurelec cochlear implant . Eur Arch Otorhinolaryngol . 2008 ; 265 : 1043 - 1046 . doi: 10.1007/s00405- 007 - 0576 - 6 PMID: 18297299
8. Graham J , Lynch C , Weber B , Stollwerck L , Wei J , Brookes G. The magnetless Clarion cochlear implant in a patient with neurofibromatosis 2 . J Laryngol Otol . 1999 ; 113 : 458 - 463 . PMID: 10505162
9. Weber BP , Neuburger J , Goldring JE , Santogrossi T , Koestler H , Baltmer RD , et al. Clinical results of the CLARION magnetless cochlear implant . Ann Otol Rhinol Laryngol Suppl . 1999 ; 177 : 22 - 26 . PMID: 10214796
10. Wackym PA , Michel MA , Prost RW , Banks KL , Runge-Samuelson CL , Firszt JB . Effect of magnetic resonance imaging on internal magnet strength in Med-El Combi 40+ cochlear implants . Laryngoscope . 2004 ; 114 : 1355 - 1361 . PMID: 15280707
11. Gubbels SP , McMenomey SO . Safety study of the Cochlear Nucleus 24 device with internal magnet in the 1.5 Tesla magnetic resonance imaging scanner . Laryngoscope . 2006 ; 116 : 865 - 871 . PMID: 16735911
12. Youssefzadeh S , Baumgartner W , Dorffner R , Gstöttner W , Trattnig S. MR compatibility of Med EL cochlear implants: clinical testing at 1 .0 T. J Comput Assist Tomogr. 1998 ; 22 : 346 - 350 . PMID: 9606372
13. Baumgartner WD , Youssefzadeh S , Czerny C , Hamzavi J , Adunka O , Gstöttner W. Clinical utilization of magnetic resonance imaging for patients with cochlear implants . Wien Klin Wochenschr 2000 ; 112 : 512 - 514 (article in German). PMID: 10890131
14. Baumgartner WD , Youssefzadeh S , Hamzavi J , Czerny C , Gstoettner W. Clinical application of magnetic resonance imaging in 30 cochlear implant patients . Otol Neurotol . 2001 ; 22 : 818 - 822 . PMID: 11698802
15. Crane BT , Gottschalk B , Kraut M , Aygun N , Niparko JK . Magnetic resonance imaging at 1.5 T after cochlear implantation . Otol Neurotol . 2010 ; 31 : 1215 - 1220 . doi: 10.1097/MAO.0b013e3181ec1d61 PMID: 20729783
16. Schmerber S , Reyt E , Lavieille JP. Is magnetic resonance imaging still a contraindication in cochlearimplanted patients? Eur Arch Otorhinolaryngol . 2003 ; 260 : 293 - 294 . PMID: 12883949
17. Fritsch MH , Mosier KM . MRI compatibility issues in otology . Curr Opin Otolaryngol Head Neck Surg . 2007 ; 15 : 335 - 340 . PMID: 17823550
18. Hochmair ES . MRI safety of MED-EL C40/C40+ cochlear implants . Cochlear Implants International . 2001 ; 2 : 98 - 114 . doi: 10.1002/cii.42 PMID: 18792092
19. Abrams HL . Cochlear implants are a contraindication to MRI . JAMA. 1989 ; 261 : 46 .
20. Baumgartner WD , Youssefzadeh S , Czerny C , Franz P , Hamzavi J , Gstöttner W. Clinical application of magnetic resonance imaging in cochlear-implanted patients . Adv Otorhinolaryngol . 2000 ; 57 : 28 - 31 . PMID: 11892168
21. Dubrulle F , Sufana Iancu A , Vincent C , Tourrel G , Ernst O. Cochlear implant with a non-removable magnet: preliminary research at 3-T MRI . Eur Radiol . 2013 ; 23 : 1510 - 1518 . doi: 10.1007/s00330- 012 - 2760 - 3 PMID: 23300043
22. Alberty J , Filler TJ , Schmäl F , Peuker ET . Thiel method fixed cadaver ears. A new procedure for graduate and continuing education in middle ear surgery . HNO . 2002 ; 50 : 739 - 742 . PMID: 12243029
23. Majdani O , Leinung M , Rau T , Akbarian A , Zimmerling M , Lenarz T , et al. Demagnetization of cochlear implants and temperature changes in 3.0 T MRI environment. Otolaryngol Head Neck Surg . 2008 ; 139 : 833 - 839 . doi: 10.1016/j.otohns. 2008 . 07.026 PMID: 19041512
24. Migirov L , Wolf M. Magnet removal and reinsertion in a cochlear implant recipient undergoing brain MRI . ORL J Otorhinolaryngol Relat Spec . 2013 ; 75 : 1 - 5 . doi: 10.1159/000346239 PMID: 23364345
25. Nucleus 24: magnetic resonance imaging (MRI) . Available: http://www.professionals. cochlearamericas.com/sites/default/files/resources/MRI.pdf. Accessed 2013 Oct 1.
26. MR safety information for the MED-El Mi1200 Synchrony implant; Available : http://www.medel. com/ synchrony-mri . Accessed 2015 Jan 1.
27. Tysome JR , Macfarlane R , Durie-Gair J , Donnelly N , Mannion R , Knight R , et al. Surgical management of vestibular schwannomas and hearing rehabilitation in neurofibromatosis type 2 . Otol Neurotol . 2012 ; 33 : 466 - 472 . doi: 10.1097/MAO.0b013e318248eaaa PMID: 22334163
28. Deneuve S , Loundon N , Leboulanger N , Rouillon I , Garabedian EN . Cochlear implant magnet displacement during magnetic resonance imaging . Otol Neurotol . 2008 ; 29 : 789 - 1190 . doi: 10.1097/MAO. 0b013e3181825695 PMID: 18667941
29. Yun JM , Colburn MW , Antonelli PJ . Cochlear implant magnet displacement with minor head trauma . Otolaryngol Head Neck Surg . 2005 ; 133 : 275 - 277 . PMID: 16087027
30. Bittencourt AG , Alves RD , Ikari LS , Burke PR , Gebrim EM , Bento RF . Intracochlear schwannoma: diagnosis and management . Int A Otorhinolaryngol . 2014 ; 18 : 322 - 324 .
31. Tieleman A , Casselmann JW , Somers T , Delanote J , Kuhweide R , Ghekiere J , et al. Imaging of intralabyrinthine schwannomas: A retrospective study of 52 cases emphasis on lesion growth . Am J Neuroradiol . 2008 ; 29 : 898 - 905 . doi: 10.3174/ajnr. A1026 PMID: 18321986
32. Todt I , Rademacher G , Mittmann P , Wagner J , Mutze S , Ernst A. MRI artifacts and cochlear implant positioning at 3T in vivo . Otol Neurotol . 2015 doi: 10.1097/MAO.0000000000000720
33. Czerny C , Gstoettner W , Franz P , Baumgartner WD , Imhof H. CT and MR imaging of acquired abnormalities of the inner ear and cerebellopontine angle . Eur J Radiol 2001 ; 40 : 105 - 112 . PMID: 11704357
34. Fruauff K , Coffey K , Chazen JL , Phillips CD . Temporal bone imaging . Review article. Top Magn Reson Imaging . 2015 ; 24 : 39: 55 .