Signal loss can extend more than 10 cm from the implant when using a spin echo–based sequence, an imaging technique that is typically robust in the presence of magnetic field inhomogeneities ( 4). The local magnetic field from the implant also makes image artifacts notably worse. The patient may experience significant discomfort due to movement of the implant magnet and may need additional preparation before the examination. Cochlear implants that contain a small magnet create a particular challenge at MR imaging. Food and Drug Administration (FDA) approval and European Economic Area (EAA) CE marking as ASTM MR Conditional with specific conditions to image at 1.5 T, and at least one device is also MR Conditional for 3 T. However, several manufacturers now offer cochlear implants containing an internal magnet that have both U.S. Many early cochlear implant models have never been MR imaging safety tested and are still considered MR Unsafe (using the ASTM International standard) in any MR imaging environment ( 3). Safety and image quality concerns exist when performing an MR imaging examination on a patient with unilateral or bilateral cochlear implants ( 1, 2). The internal components of the implant-the active circuitry, electrodes, receiver antenna, and magnet-interact with various components of the MR imaging unit. When these patients require a magnetic resonance (MR) imaging examination, the implanted components of the device introduce complexity to both patient preparation and image acquisition. 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.Ĭochlear implants and auditory brainstem implants (ABIs) have dramatically improved the quality of life for many patients with severe to profound sensorineural hearing loss. Diseases such as neurofibromatosis type 2 that are associated with bilateral vestibular schwannomas and hearing loss often require lifelong tumor surveillance with MR imaging. Translational forces and torque sometimes displace the implanted magnet even when a head wrap is used. 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. Each examination may require impromptu adjustments to allow visualization of the tissue or contrast of interest. Typical artifacts at diffusion-weighted imaging and accelerated imaging are exacerbated. Fat-saturation failures and susceptibility artifacts severely degrade image quality. 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. Food and Drug Administration and European Economic Area regulatory approval to allow magnetic resonance (MR) imaging examinations to be performed under certain specified conditions. Several cochlear implant models have recently received U.S. A small magnet within the internal component is commonly used to hold the external speech processor unit in place. These implants consist of an internal component implanted between the skull and the temporal scalp and an external removable speech processor unit. The number of patients receiving cochlear implants and auditory brainstem implants for severe to profound sensorineural hearing loss has rapidly increased.
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