Magnetic properties of middle ear and stapes implants in a 9.4-T magnetic resonance field.
OBJECTIVE
A 9.4-T magnetic resonance (MR) field may cause motion displacement of the middle ear and stapes implants not previously observed with 1.5- and 3.0-T magnets.


BACKGROUND
Publications have described the safety limitations of some otologic implants in 4.7-T field and resulted in several companywide patient safety-related recalls. To date, no studies have been reported for otologic implants in a 9.4-T MR field nor have comparisons been made with 4.7-T field strengths.


METHODS
Twenty-three commonly used middle ear and stapes prostheses were selected and exposed to 9.4-T MR fields in vitro within petri dishes, and eight of the 23 implants were further studied ex corpus in human temporal bones (TBs) in a 9.4-T MR field. This study has been approved by the institutional review board.


RESULTS
Eight prostheses in petri dishes grossly displaced at 9.4 T, three of which had not previously moved in either the 1.5- or 3.0-T magnets. The eight TB preparations showed no avulsions or motion indicators after exposure at 9.4 T.


CONCLUSIONS
Middle ear and stapes implants can move dramatically in petri dishes at 9.4-T MR field, more so than at 1.5 and 3.0 T. The absence of avulsions in the TB group strongly suggests that the surgical means used to fixate the middle ear implants to the middle ear structures successfully overcomes the magnetic moment produced at MR field strengths up to 9.4 T. The use of MR imaging is not contraindicated by this study's findings.
Fritsch
Michael H
MH
Department of Otolaryngology-Head and Neck Surgery, Indiana University Medical Center, Indianapolis, Indiana 46202, USA. mfritsch@iupui.edu
Gutt
Jason J
JJ
Naumann
Ilka C
IC
D002102:Cadaver; D019544:Equipment Failure Analysis; D005290:Ferric Compounds / Q000009:adverse effects*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000009:adverse effects*; D009998:Ossicular Prosthesis; D019933:Ossicular Replacement / Q000379:methods; D014732:Vibration / Q000009:adverse effects
D005290:Ferric Compounds; C001215:ferrite