Department of Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria.
Otol Neurotol. 2010 Jun;31(4):676-80. doi: 10.1097/MAO.0b013e3181d2d3f3.
Is the human ossicular chain stabile enough to withstand the torque of a Vibrant Soundbridge middle ear hearing implant in the magnetic field of a 1.5 T magnetic resonance imaging (MRI) system?
The Vibrant Soundbridge is a semi-implantable hearing device in which a tiny electromechanical transducer, called floating mass transducer (FMT), is clipped to the ossicular chain within the middle ear. The FMT contains a permanent magnet, which can generate a torque when exposed to a static magnetic field of MRI systems. Since the transducer is routinely attached to the long process of the incus, this torque could affect or even disrupt the ossicular chain. This study investigates the likelihood of a middle ear injury by an FMT in an MRI system.
Torque measurements were performed on 10 unpreserved human temporal bones. A brass fork was attached to the long process of the incus via a posterior tympanotomy, and a defined torque was applied by a calibrated torque meter. The torque was increased stepwise until an injury of the middle ear was observed.
The mean torque at which the middle ear was injured was 4.3 mN.m +/- 1.7 mN.m. The lowest value measured was 1.5 mN.m, and the highest was 6.5 mN.m.
Even the lowest torque measured is more than 1.5 times higher than the "worst-case" torque affecting the FMT during a 1.5 T MRI examination. The torque on an FMT crimped to the long process of the incus should therefore not harm the human middle ear.
在 1.5T 磁共振成像（MRI）系统的磁场中，人类听小骨链是否稳定到足以承受 Vibrant Soundbridge 中耳植入物的扭矩？
Vibrant Soundbridge 是一种半植入式听力设备，其中一个微小的机电换能器，称为浮动质量换能器（FMT），夹在中耳的听小骨链上。FMT 包含一个永磁体，当暴露于 MRI 系统的静磁场时，它会产生扭矩。由于换能器通常附着在砧骨的长突上，因此这种扭矩可能会影响甚至破坏听小骨链。本研究旨在调查 FMT 在 MRI 系统中引起中耳损伤的可能性。
对 10 个未经保存的人颞骨进行扭矩测量。通过后鼓室切开术将一个黄铜叉附着在砧骨的长突上，并通过校准的扭矩计施加一定的扭矩。逐步增加扭矩，直到观察到中耳损伤。
中耳损伤的平均扭矩为 4.3mN.m+/-1.7mN.m。测量到的最小值为 1.5mN.m，最大值为 6.5mN.m。
即使测量到的最小扭矩也高于 1.5T MRI 检查中影响 FMT 的“最坏情况”扭矩的 1.5 倍以上。因此，夹在砧骨长突上的 FMT 产生的扭矩不应损害人类中耳。
