From the Departments of Radiology (H.A.E., A.C.P., R.E.W.) and Otorhinolaryngology (M.L.C.), Mayo Clinic, 200 First St SW, Rochester, MN 55905.
Radiographics. 2018 Jan-Feb;38(1):94-106. doi: 10.1148/rg.2018170135.
The number of patients receiving cochlear implants and auditory brainstem implants for severe to profound sensorineural hearing loss has rapidly increased. These implants consist of an internal component implanted between the skull and the temporal scalp and an external removable speech processor unit. A small magnet within the internal component is commonly used to hold the external speech processor unit in place. Several cochlear implant models have recently received U.S. Food and Drug Administration and European Economic Area regulatory approval to allow magnetic resonance (MR) imaging examinations to be performed under certain specified conditions. The small internal magnet presents a challenge for imaging of the head and neck near the implant, creating a nonlinear magnetic field inhomogeneity and significant MR imaging artifacts. Fat-saturation failures and susceptibility artifacts severely degrade image quality. Typical artifacts at diffusion-weighted imaging and accelerated imaging are exacerbated. Each examination may require impromptu adjustments to allow visualization of the tissue or contrast of interest. Patients may also be quite uncomfortable during the examination, as a result of either imposed magnetic forces or a tight head wrap that is often applied to minimize internal magnet movement. Translational forces and torque sometimes displace the implanted magnet even when a head wrap is used. Diseases such as neurofibromatosis type 2 that are associated with bilateral vestibular schwannomas and hearing loss often require lifelong tumor surveillance with MR imaging. A collaborative team of radiologists, technologists, and/or medical physicists or MR imaging scientists, armed with strategies to mitigate artifacts near implanted magnets, can customize the examination for better visualization of tissue and consistent comparison examinations over time. RSNA, 2018.
越来越多患有重度至极重度感音神经性听力损失的患者接受了人工耳蜗和听觉脑干植入物的治疗。这些植入物包括一个植入在颅骨和颞骨头皮之间的内部组件和一个外部可移动的言语处理器单元。内部组件中的一个小磁铁通常用于将外部言语处理器单元固定在位。最近，几种人工耳蜗模型已获得美国食品和药物管理局和欧洲经济区的监管批准，允许在特定条件下进行磁共振（MR）成像检查。小的内部磁铁对植入物附近的头颈部成像构成了挑战，产生了非线性磁场不均匀和显著的磁共振成像伪影。脂肪饱和失败和磁化率伪影严重降低了图像质量。弥散加权成像和加速成像的典型伪影加剧。每次检查可能需要即兴调整以允许可视化感兴趣的组织或对比度。由于施加的磁场或经常用于最小化内部磁铁运动的紧绷头带，患者在检查过程中也可能会感到非常不适。即使使用头带，翻译力和扭矩有时也会使植入的磁铁移位。与双侧听神经瘤和听力损失相关的神经纤维瘤病 2 等疾病通常需要终生进行磁共振成像肿瘤监测。放射科医生、技术人员和/或医学物理学家或磁共振成像科学家组成的协作团队，配备了减轻植入磁铁附近伪影的策略，可以为更好地可视化组织和随着时间的推移进行一致的比较检查定制检查。RSNA，2018 年。
