MRI and Cochlear Implants
The issue of Magnetic Resonance Imaging (MRI) is an important issue for many families considering a cochlear implant. One of the key benefits of the Nucleus 3 system is the removable magnet, which allows safe and easy access to MRI medical technology. Cochlear is the only manufacturer that creates a cochlear implant with a removable magnet. The presence of a removable magnet is a standard feature that provides candidates and recipients with two options, either removing the magnet at the time of a required MRI or implanting the device without the magnet. The magnet is removed during a simple outpatient procedure under local anesthetic. The physician makes a small incision over the receiver/stimulator behind the ear and removes the magnet. The incision is covered with a sterile bandage. Once the MRI is complete the magnet is replaced, and the incision is closed. Should a candidate/physician choose to have the device implanted without a magnet there is a retainer disc available. These adhesive discs contain a magnet and keep the external transmitter coil on the head.
Once the magnet is removed, the Nucleus internal implant is designed to be unaffected by the magnetic fields of an MRI up to 1.5 Tesla. Tesla is a unit of measure used to rate the strength of a magnet in the MRI equipment. The standard of care for MRI scans in the U.S. is 1.5 Tesla. (Source: Diagnostic Imaging Scan MRI Market Report 1998)The magnets in MRI equipment most frequently used today are in the 0.5 Tesla to 2.0 Tesla range . 75% of the U.S. installed base of MRI systems have field strength greater than 0.5 Tesla. Higher magnetic field strengths provide clearer, more detailed images, important for the diagnosis of many types of injuries and conditions. Other implant systems have been tested and reported to be unaffected by MRI up to 0.3 Tesla, but fewer than 20% of MRI machines installed in the U.S. operate at such low field strengths.