Biomechanical influences of magnetic resonance imaging on the SOUNDTEC Direct System implant.
OBJECTIVE
The purpose of this study was to measure the forces experienced by the SOUNDTEC Direct System magnetic implant during 0.3-T MRI.


METHODS
Torsional and linear forces imposed on 8 implants were measured by using calibrated neurologic Von Frey hairs and were compared with finite-element analysis predictions and the forces required to separate the incudostapedial joints of unpreserved temporal bones. An implanted embalmed autopsy specimen was also examined before and after 1.5-T MRI.


RESULTS
Peak linear force at the orifice of the MRI core measured 0.51g (+/-0.2 SD). Maximum torque occurred at the MRI core center and measured 11.4g-cm (+/-1.2 SD). The mean torque required to separate the incudostapedial joints of 12 unpreserved temporal bones was 33.8g-cm (+/-20.4 SD). The autopsy specimen sustained a 1.5-T MRI scan without disruption of the ossicular chain or explantation.


CONCLUSIONS
Physical and mechanical testing of the SOUNDTEC implant indicates that the structural integrity of the ossicles will be maintained during 0.3-T MRI of the human head.
Dyer
Robert Kent
RK
Hough Ear Institute, University of Oklahoma Health Sciences Center, 3400 NW 56th Street, Oklahoma City, OK 73112-4466, USA. kentdyer@swbell.net
Dormer
Kennet J
KJ
Hough
J V D
JV
Nakmali
Udon
U
Wickersham
Rick
R
D001696:Biomechanical Phenomena; D003054:Cochlear Implants / Q000592:standards*; D019245:Compressive Strength; D003257:Consumer Product Safety; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics; D011474:Prosthesis Design; D012680:Sensitivity and Specificity; D013701:Temporal Bone / Q000502:physiology