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

Abstract

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.

Magnetic Resonance Imaging Compatibility and Safety of the SOUNDTEC Direct System

“…Linear and torsional forces associated with the static field were measured in this study using calibrated VHF placed into contact with the implant and allowed to oppose movement of the implant toward the MRI core. Linear force was greatest at the MRI entry point and measured 0.5 g. This force is 60 times less than the force (30 g) required to temporarily stretch the incudostapedial joint during pull tests performed on an implanted autopsy specimen and in fresh human temporal bones previously evaluated 40 . Torsional force on the SOUNDTEC implant using the VFH technique was greatest at the center of the MRI core and measured 11.4 g cm.…”

“…No conclusions about MRI safety or compatibility can be made for the SOUNDTEC Direct System in magnetic fields higher than 0.3 Tesla until further studies are performed. However, previous studies of implanted autopsy specimens suggest that the SOUNDTEC implant is mechanically stable at field strengths of 1.5 Tesla 40 …”

“…Maximum torque was predicted mathematically using the equation: where M imp = magnetization of the implant magnetic material per unit volume and Bo MRI = the external magnetic field at the center of the 0.3‐Tesla MRI. Using this mathematical formula, peak torque on the SOUNDTEC Direct System implant was 9.6 g cm 40 …”

Implantable Hearing Devices

“…Both linear and torsional forces affect the implant in a magnetic field, with the latter being more significant and potentially leading to displacement of the implant and/or ossicular chain. 11 Also contributing to the MRI risk are heating of the magnet (creating the potential for surrounding tissue damage), implant demagnetization, and image distortion/degradation. Because of these risks, the official manufacturer recommendation is that patients with the MAXUM system should not undergo MRI or be in close proximity to magnetic fields.…”

Gestörtes HörenDie apparative Versorgung der Schwerhörigkeit: Konventionelle und implantierbare Hörgeräte

“…Allerdings bleibt damit dennoch ein wesentlicher Makel konventioneller Hörgeräte bestehen, nämlich die Gehörgangsokklusion durch dieses Ohrpassstück. Wie bei den beiden vorgenannten implantierbaren Hörgeräten ist auch beim Soundtec Direct Drive System die Durchführung einer Kernspintomografie ohne Entfernung des Magneten kontraindiziert [47].…”