Effect of magnetic resonance imaging on internal magnet strength in Med-El Combi 40+ cochlear implants.
OBJECTIVE
Magnetic resonance imaging (MRI) has been contraindicated when cochlear implants containing an internal magnet are in place because of concerns regarding torque, force, demagnetization, artifacts, induced voltages, and heating. The objective was to determine the magnetic field strength of Med-El Combi 40+ cochlear implant internal magnets after MRI studies.


METHODS
Two fresh cadavers were used to study demagnetization using a repeated measures design and a magnetometer. Pre- and postMRI measurement of magnetic field strength was completed. Five sets of sagittal T1-weighted, axial T1-weighted, and axial T2-weighted sequences were performed on a cadaver at 0.2 Tesla in the device-up and device-down positions. In the other cadaver, 15 sets of sagittal T1-weighted, axial T1-weighted, and axial T2-weighted sequences were performed on a cadaver at 1.5 Tesla were conducted, 5 each with the head oriented at 80, 90, and 100 degrees rotated around the yaw plane (rotated around the z-axis). Subsequently, three cochlear implant patients completed 0.2 Tesla MRIs. For these patients, subjective and objective assessment of cochlear implant performance was performed.


METHODS
Academic medical center.


RESULTS
In the cadaver studies, analysis of variance showed no significant difference in the magnetic field strength after the 0.2 or 1.5 Tesla scans. There was no significant difference in the magnetic field strength for the three patients undergoing 0.2 Tesla MRIs and no adverse consequences, including no changes in telemetry, auditory sensations, nonauditory sensations, and sound quality.


CONCLUSIONS
No significant demagnetization of the internal magnet occurred during repeated 1.5 Tesla MRI scans with the head orientations used in this study. In the cochlear implant patients, no significant demagnetization of the internal magnet occurred after a 0.2 Tesla MRI.
Department of Otolaryngology and Communication Sciences, Medical College of Wisconsin, Milwaukee, WI 53226, USA. wackyn@mcw.edu
P Ashley
PA
Wackym
Michelle A
MA
Michel
Robert W
RW
Prost
Kristin L
KL
Banks
Christina L
CL
Runge-Samuelson
Jill B
JB
Firszt
D016477:Artifacts; D003054:Cochlear Implants; D000075202:Contraindications; D006801:Humans; D066298:In Vitro Techniques; D008279:Magnetic Resonance Imaging / Q000009:adverse effects; D008280:Magnetics