Bone Conduction ImplantsAre bone conduction implants safer than cochlear implants for MRI?
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Bone conduction hearing aids capture sound and transfer it via bone vibrations directly to the cochlea, thus bypassing the outer and middle ear. Surgically implanted, they are classified as either percutaneous or transcutaneous.
Percutaneous bone conduction implants consist of a titanium post (screwed into the skull and protruding through the skin) to which a removable external sound processor is attached. Examples include the Oticon Pronto and Cochlear™ Baha® Connect.
Transcutaneous bone conduction implants do not have elements penetrating the skin. Passive transcutaneous implants like the Cochlear™ Baha® Attract and Medtronic Alpha 2 MPO ePlus™ have an internal magnet bolted to the skull which receives vibrations from a removable external sound processor and magnet. Active transcutaneous devices, like the Med-El Bonebridge and Cochlear™ Osia®, are similar to cochlear implants in that they have subcutaneously implanted electronic components, including a magnet, receiver coil, and stimulator. Signals are transferred electromagnetically across the skin from a removable external microphone, magnet, and sound processor. The final output from the internal device goes to a vibrating piezoelectric transducer attached to the skull.
Pronto passive percutaneous bone conduction implant (Courtesy Oticon Medical, Inc.)
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Baha® Attract passive transcutaneous bone conduction implant (Courtesy Cochlear, Inc)
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Bonebridge active transcutaneous bone implant with implanted transducer (Courtesy Med-El)
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Three major types of Bone Conduction Hearing Implants
In general we would expect passive bone conduction implants to have an equal or better safety profile than cochelar implants because of their secure attachment to the skull. Of course, all external components must be removed prior to entering the scanner room. All commercially produced bone conduction implants are considered MR Conditional, which may impose some limits on field strength, spatial gradient, slew rate, switched gradient amplitude, SAR, and whether internal magnet removal is required. As always, the manufacturer's web site should be consulted for up-to-date product information and recommendations regarding scanning.
References
Azadarmaki R, Tubbs R, Chen DA, Shellock FG. MRI information for commonly used otologic implants: review and update. Otolaryngol Head Neck Surg 2014;150:512-9. [DOI LINK]
Reinfeldt S, Håkansson B, Taghavi H, Eeg-Olofsson M. New developments in bone-conduction hearing implants: a review. Med Devices: Evidence Res 2015; 8:79-93. [DOI LINK]
Schneider ML, Walker GB, Dormer KJ. Effects of magnetic resonance imaging on implantable permanent magnets. Am J Otol 1995; 16:687-9. (case report of a patient with a Xiomed Audient magnetic implant, an early type of transcutaneous passive device, that became demagnetized after a 1.5T scan)
Azadarmaki R, Tubbs R, Chen DA, Shellock FG. MRI information for commonly used otologic implants: review and update. Otolaryngol Head Neck Surg 2014;150:512-9. [DOI LINK]
Reinfeldt S, Håkansson B, Taghavi H, Eeg-Olofsson M. New developments in bone-conduction hearing implants: a review. Med Devices: Evidence Res 2015; 8:79-93. [DOI LINK]
Schneider ML, Walker GB, Dormer KJ. Effects of magnetic resonance imaging on implantable permanent magnets. Am J Otol 1995; 16:687-9. (case report of a patient with a Xiomed Audient magnetic implant, an early type of transcutaneous passive device, that became demagnetized after a 1.5T scan)
Related Questions
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