MRIs may damage cochlear implants

NEW YORK (Reuters Health) - Tests show that certain MRI machines may demagnetize the magnets used in cochlear implants to couple external and implanted components of these hearing devices, according to a report in the December issue of Otolaryngology–Head and Neck Surgery.

Cochlear implants may be an option for those with severe hearing loss. It involves a surgical procedure in which a small electronic device is placed under the skin behind the ear and attached to a wire that stimulates the inner ear, allowing the recipient to hear useful sounds.

Cochlear implants also contain internal magnets used to connect an external processor with the surgically implanted components, Dr. Omid Majdani, of the Medical University of Hannover, Germany, and colleagues explain. These magnets can interact with other magnets, such as those found in magnetic resonance imaging (MRI) machines. MRIs exert strong magnetic fields that may induce voltages or temperatures that could damage the implant or harm the patient.

The researchers examined the extent of damage to the magnets and the temperature changes in cochlear implants exposed to an MRI machine.

They found that demagnetization of the cochlear implant magnets depends on the angle between the magnetic field of the magnet and the MRI. When the angle between the MRI magnet and the implant magnet is greater than 80 degrees, demagnetization reached unacceptable levels.

The maximum temperature increase in the cochlear implants was 0.5 degrees C, within the acceptable limit of 1.0 degrees in any location.

“Although little to no demagnetization occurred if the angle between the poles of the cochlear implant magnet and MRI magnet was up to 80 degrees, identification of magnetic poles is not uniform between patients or scanners,” Majdani’s team found. “Extensive procedural changes would be necessary to ensure that a safe orientation was maintained” before patients with cochlear implants can safely undergo MRI testing.

SOURCE: Otolaryngology–Head and Neck Surgery, December 2008.

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