Transcript ResearchPresentations\Artificial Cochlear Implants

Abstract: When natural hearing is lost, cochlear implants
provide an opportunity to restore hearing. These electronic
devices are surgically implanted into a person’s cochlea and
act as a replacement ear to bypass the damaged systems
preventing normal hearing. The most significant part of these
devices are the electrodes, which connect the electrical device
to the biological system.
Nick Hamilton
EE 4611
27 April 2015
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Introduction to Cochlear Implants
Overview of How the Ear Functions
Design and Function of Cochlear Implants
Impact of Semiconductors
Pros and Cons
Comparison to Other Devices
Future of Cochlear Implants
Alessandro Volta first stimulated the ear in 1800 using
electricity.
The first implants did not exist until around 1950.
The FDA allowed them to be implanted in adults in 1984.
Since 2000, the implants are approved for infants over 12
months old.
The sooner a cochlear implant can be used to restore hearing,
the better chances of success. In some cases, the brain will not
recognize the signals being sent. This often occurs if a person
has been deaf for a very long time.
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Outer Ear
◦ Canal
◦ Drum
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Middle Ear
◦ Malleus
◦ Incus
◦ Stapes
These are the three smallest
Bones in the human body.
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Inner Ear
◦ Cochlea
◦ Auditory Nerve
Sound enters the ear canal and contacts the ear
drum. The vibrations are amplified by the
malleus, incus, and stapes. This produces fluid
waves in the cochlea. Tiny hairs in the cochlea
transform these waves into signals sent to the
brain. The deepest part of the cochlea responds
to the lowest frequencies.
External
Microphone
Speech Processor
Transmitter
Internal
Receiver
Electrode Array
Converts sound to electrical signals that are sent to the speech
processor.
Good microphones have a broad range of frequency response,
but are designed not to pick up lower frequencies. Sounds in
this range include head movement and walking.
A directional microphone will detect sound better in the
direction it is facing. This can aid in picking up sound from
conversations, especially in noisy environments.
Piezoelectric microphones allow microphone size to be reduced
while improving signal quality.
Software is capable of creating more frequencies than there are
electrodes by stimulating two adjacent electrodes at once. This
effectively enhances resolution. For example: An array with 16
electrodes has 15 possible pairs. This equates to 15 times the
number of possible channels per pair. If 8 distinct channels can
be created per pair, then 120 possible pitches may be generated.
These in-between pitches are called virtual channels.
Information is sent through a radio frequency signal from the
speech processor to the implanted component.
A direct connection (wire) allows for superior transmission, but
has a high chance of infection. This method is not used.
On the left are the connections for the implantable device.
The electrode array and contacts are on the right side.
The middle is a series of wave shaped wires surrounded
by silicon.
Overall length is 100 mm.
The array is between 0.8 and 0.5 mm in diameter.
Inside the silicon casing are small wires.
Each wire carries one channel of sound.
The wires and contacts are 90% platinum and 10% iridium.
These metals form a strong, conductive wire.
Cochlear implants are currently not intended to solve all degrees
of hearing loss.
They are best suited for those who have lost all or nearly all
natural hearing.
Current cochlear implants cannot fix hearing loss as a result of
nerve damage.
Implants can bypass damaged parts of the ear, except the nerve,
and restore some hearing.
The use of cochlear implants will cause a person to lose all
natural hearing, if they have any left.
These implants are the only possibility for correcting complete
loss of hearing in any person who does not have nerve damage.
In any case where someone retains a measurable amount of
hearing, other solutions are preferred, if possible.
Some of these other options:
Hearing Aids – Amplify sound in ranges where hearing
loss exists
Middle Ear Implants – Must rely on a fully functional
cochlea. Replaces middle ear and also requires an external audio
processor.
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Biologically Friendly Materials:
◦ Silicon: Used to encase the implant.
◦ Titanium: Used in the central part of the implant.
◦ Platinum: Used for the contacts.
These materials are used because they do not react with anything inside the
body. These materials also have excellent long-term stability. This means
that they do not degrade or cause any issues after being implanted for a
long period of time.
As the device feature size decreases in fabrication techniques,
more features may become available to cochlear implants.
The largest factor limiting the quality of these implants is the
electrode array. The more channels possible, the better the
frequency response and sound quality become. Fabrication may
allow for smaller electrodes, meaning more of them can be used
in an implant.
Smaller device size also leads to smaller external components,
providing more attractively sized external hardware with more
capability.
In order to carry more channels of sound, the amount of wires
used to transmit into the cochlea must be increased.
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The final sound quality of a cochlear implant is comparable to
that of an out-of-tune radio. Some describe it as sounding
“robotic.”
Without context, it is difficult to understand some sounds
generated by these implants. Speech recognition is possible.
Advantages:
Hearing is recovered
immediately after surgery.
Speech recognition, possibly
without lip-reading.
Disadvantages:
High cost: $40,000 - $100,000
Any natural hearing will be lost.
Electromagnetic noise.
Can detect a variety of sounds.
Anti-theft sensors may detect
implants.
Some people may enjoy music.
External components may be
damaged by water.
Components are upgradeable.
Physical contact may damage
implant.
Increased independence.
Many diseases and infections
There are no other devices that will resolve hearing loss at the
range that cochlear implants are meant to.
All other options provide superior sound quality and are
preferred if at all possible.
Other options are much cheaper than cochlear implants.
Many do not require surgery.
All solutions require a battery to power circuitry.
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Add additional sound channels
Water resistivity
Completely internalize components
Better frequency resolution (more channels)
Improved battery life
Lower manufacturing/medical cost
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How the Ear Functions
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Hearing Loss and Cochlear Implants
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Device Layout
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Improvements
Information:
http://www.hopkinsmedicine.org/hearing/hearing_loss/how_the_ear_works.html
http://www.bcig.org.uk/cochlear-implant-devices/implantable-devices/
http://www.nidcd.nih.gov/health/hearing/pages/coch.aspx
http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/ImplantsandProst
hetics/CochlearImplants/ucm062823.htm
http://www.medel.com/blog/close-up-with-cochlear-implant-electrode-arrays/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3199815/
http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/ImplantsandProst
hetics/CochlearImplants/ucm062843.htm
http://biomed.brown.edu/Courses/BI108/2006108websites/group10cochlearimplant
/pages/microphone.html
Pictures:
http://www.newleafhearing.com/hearing-loss/how-the-ear-works/
http://www.medel.com/us/about-hearing/
http://www.nyee.edu/patient-care/medical-information/cochlear-implants
http://cochlearimplanthelp.com/journey/choosing-a-cochlear-implant/electrodesand-channels/
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Sound travels into the ear, contacts the eardrum, and creates
mechanical vibrations. These vibrations create waves in the
cochlea that are detected by tiny hairs and transmitted through
nerves as sound.
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Cochlear implants directly stimulate the nerve cells in the
cochlea.
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Main components: Microphone, speech processor, transmitter,
and electrode array.
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Materials used are silicon, titanium, and platinum because they
do not interfere or interact with the body when implanted.
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The electrodes do not provide precise stimulation and do not
allow for extremely high audio quality.