Luechinger Roger, Boesiger Peter, Disegi John A
Institute for Biomedical Engineering, University and ETH Zurich, Switzerland.
J Biomed Mater Res B Appl Biomater. 2007 Jul;82(1):17-22. doi: 10.1002/jbm.b.30699.
Large orthopedic external fixation clamps and related components were evaluated for force, torque, and heating response when subjected to the strong electromagnetic fields of magnetic-resonance (MR) imaging devices. Forces induced by a 3-Tesla (T) MR scanner were compiled for newly designed nonmagnetic clamps and older clamps that contained ferromagnetic components. Heating trials were performed in a 1.5 and in a 3 T MR scanner with two assembled external fixation frames. Forces of the newly designed clamps were more than a factor 2 lower as the gravitational force on the device whereas, magnetic forces on the older devices showed over 10 times the force induced by earth acceleration of gravity. No torque effects could be found for the newly designed clamps. Temperature measurements at the tips of Schanz screws in the 1.5 T MR scanner showed a rise of 0.7 degrees C for a pelvic frame and of 2.1 degrees C for a diamond knee bridge frame when normalized to a specific absorption rate (SAR) of 2 W/kg. The normalized temperature increases in the 3 T MR scanner were 0.9 degrees C for the pelvic frame and 1.1 degrees C for the knee bridge frame. Large external fixation frames assembled with the newly designed clamps (390 Series Clamps), carbon fiber reinforced rods, and implant quality 316L stainless steel Schanz screws met prevailing force and torque limits when tested in a 3-T field, and demonstrated temperature increase that met IEC-60601 guidelines for extremities. The influence of frame-induced eddy currents on the risk of peripheral nerve stimulation was not investigated.
对大型骨科外固定夹及相关组件在受到磁共振（MR）成像设备的强电磁场作用时的力、扭矩和热响应进行了评估。针对新设计的无磁性夹和包含铁磁组件的旧夹，汇编了由3特斯拉（T）MR扫描仪产生的力。在1.5T和3T MR扫描仪中，使用两个组装好的外固定架进行了加热试验。新设计夹所受的力比设备上的重力低两倍多，而旧设备上的磁力显示超过地球重力加速度所产生力的10倍。新设计的夹未发现扭矩效应。在1.5T MR扫描仪中，当归一化到2W/kg的比吸收率（SAR）时，Schanz螺钉尖端的温度测量显示，骨盆架温度升高0.7摄氏度，菱形膝关节桥架温度升高2.1摄氏度。在3T MR扫描仪中，骨盆架归一化温度升高0.9摄氏度，膝关节桥架归一化温度升高1.1摄氏度。用新设计的夹（390系列夹）、碳纤维增强杆和植入级316L不锈钢Schanz螺钉组装的大型外固定架，在3T磁场中测试时满足了主要的力和扭矩限制，并显示出符合IEC - 60601四肢指南的温度升高。未研究框架感应涡流对周围神经刺激风险的影响。
