Biomechanical Influences of Magnetic Resonance Imaging on the SOUNDTEC Direct System Implant

Abstract

OBJECTIVE: The purpose of this study was to measure the forces experienced by the SOUNDTEC Direct System magnetic implant during 0.3-T MRI. STUDY DESIGN: 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 0.51 g ±0.2 SD). Maximum torque occurred at the MRI core center and measured 11.4 g-cm (±1.2 SD). The mean torque required to separate the incudostapedial joints of 12 unpreserved temporal bones was 33.8 g-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.