Titanium (Ti) alloys have been introduced in magnetic resonance (MR) safe implantable medical devices because the susceptibility of Ti is approximately 1/10 that of the Co-Cr-Ni alloy (Elgiloy), which was the previously preferred MR-safe material. The torque applied to metallic materials in an MR imaging (MRI) scanner is commonly believed to increase with the susceptibility of the material. However, a visual inspection showed that the torque applied to Ti alloy cerebral aneurysm clips is comparable with that in the case of those of Elgiloy. In this study, we measured the torque applied to the small test pieces of rods and aneurysm clips quantitatively in a 3-T MRI using an accurate self-developed torque measurement apparatus. The maximum torques of Ti alloy and Elgiloy rod test pieces were comparable as 1.1 and 1.2 µN·m, respectively. The values for Ti alloy aneurysm clips were distinctly higher than the values for those of Elgiloy. These contradictory results of a larger torque for smaller-susceptibility products could be explained by our new theory, which takes into account the crystal susceptibility anisotropy in addition to the conventional torque due to the shape anisotropy.

中文翻译：

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磁共振扫描仪中钛合金脑动脉瘤夹的扭矩特性。

钛（Ti）合金已被引入磁共振（MR）安全的可植入医疗设备中，因为Ti的磁化率约为以前首选的MR安全材料Co-Cr-Ni合金（Elgiloy）的1/10。 。通常认为，在MR成像（MRI）扫描仪中施加到金属材料上的扭矩会随着材料的敏感性而增加。但是，目测表明，施加在钛合金脑动脉瘤夹上的扭矩与Elgiloy的扭矩相当。在这项研究中，我们使用精确的自行开发的扭矩测量设备在3-T MRI中定量测量了施加在小棒和动脉瘤夹上的小试件上的扭矩。Ti合金试件和Elgiloy试棒的最大扭矩分别为1.1和1.2 µN·m。钛合金动脉瘤夹的值明显高于Elgiloy的值。对于较小的磁化率产品，较大的转矩所产生的这些矛盾结果可以用我们的新理论来解释，该理论不仅考虑了由于形状各向异性而产生的常规转矩，而且还考虑了晶体磁化率的各向异性。