Cochlear implant is an implantable hearing aid device which provides a sense of sound to the person with severe to profound sensorineural hearing loss. Unlike the traditional deaf-aid, the working principle of cochlear implant is not amplifying the sound but apply electrical stimulation to the well-functioning auditory nerve in the cochlea.
How does Auditory System Work?
- Human ear can be divided into the outer ear, middle ear, and inner ear.
- Outer ear includes auricle and canal. Sound will further transmit through the canal after collecting and filtered by auricle.
- Middle ear includes the tympanic membrane and Ossicular chain. The tympanic membrane will vibrate in path with sound rhythm. The sound will translate to mechanical vibration during this process and vibration will be further entered the inner ear via Ossicular chain.
- Inner ear includes the cochlea and auditory nerve. The sound vibration will lead to the movement of cochlear fluid and thus cause the bends of hair cells. The neutral signal generated by hair cell will be picked up by the auditory nerve. Therefore, the signal will be translated into sound by the brain.
Structure of Cochlear Implant
- Cochlear implant system contains internal part and the external part.
- Internal part of cochlear implant includes receiver, decoder, and stimulator. Internal part will be placed under the skin behind the ear by surgery.
- External part includes microphone, speech processor, and transmitter. External part is always placed behind the ear.
Working Principle of Cochlear Implant
Hair cells of the deaf person are damaged or reduced due to different lesions, then residues cannot drive auditory nerve normally. For cochlear implant, the electrical stimulation will apply to the auditory nerve directly which skip to the sector of hair cells.
- Microphones collect sound and information spreads to the speech processor.
- Speech processor digitalizes, filters, and codes information.
- Digital signal spread to transmission coil through wire, then signal transmit to the receiver and stimulator under the skin.
- Receiver and stimulator decoding information.
- Electronic signal is passed to specify position of the electrode array, and hence stimulate the nerve fibers in the cochlea.
- Electronic signal is recognized as sound by the brain after nerve received the electronic signal.
MRI Compatible Cochlear Implant Magnets
Magnetic Resonance Imaging (MRI) is a common medical imaging procedure nowadays, and detailed images of internal organs and tissue can be got relied on the powerful magnetic field which generated by MRI. For cochlear implant system, the processor magnet attracts to the internal part’s magnet to hold it in place. Therefore, MRI becomes an extremely important issue for cochlear implant users. The significant risk of complications will be carried during MRI, such as pain, discomfort, and magnet’s dislocation. Cochlear implant manufacturers have introduced many solutions to solve disadvantage influence of the powerful magnetic field (1.5T and 3.0T) to internal cochlear implant magnets. In fact, how to make self-aligning cochlear implant magnets to avert surgery is still mainstream manufacturers. Magnets with special magnetization direction and isotropic NdFeB powder has been already used currently.