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Cochlear Implants. Ryan S. Clement, PhD Neural Engineering and Applications Laboratory BioE 200: September 18, 2002. Anatomy and Physiology of Hearing. External Ear. Middle Ear Bones. Cochlea. Ear Canal. Ear Drum.

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Cochlear Implants

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Cochlear implants l.jpg

Cochlear Implants

Ryan S. Clement, PhD

Neural Engineering and Applications Laboratory

BioE 200: September 18, 2002


Anatomy and physiology of hearing l.jpg

Anatomy and Physiology of Hearing

External Ear

Middle Ear Bones

Cochlea

Ear Canal

Ear Drum

Adapted from: http://funsan.biomed.mcgill.ca/~funnell/AudiLab/501/mmem003.html


Anatomy and physiology con t l.jpg

Anatomy and Physiology (con’t)

Cochlear Cross-section

http://shark.me.nus.edu.sg/~asme/MechHear.htm

Traveling Wave Movie

©Howard Hughes Medical Institute

http://www.iurc.montp.inserm.fr/cric/audition/


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Sound Transduction

Cochlea Hair Cells

Cochlear cross-section (single turn)

Basilar Membrane

Auditory Nerve

http://www.iurc.montp.inserm.fr/cric/audition/


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OHCs

IHCs

Sensorineural Hearing Loss

  • Causes

    • Heredity

    • Genetic

    • Aging process

    • Ototoxic drugs

    • Excessive exposure to loud sounds

Microscopic

view of hair

cells.


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Electrical Stimulation Can Allow Us to Bypass Damaged Haircells


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A Brief History

  • Volta (1790)

    • metal rods and battery induced sounds like boiling liquid!

  • Djourno and Eyries (1957)

    • First demonstration of direct electrical stimulation of auditory nerve

  • House and Urban (1972)

    • Develop and test first prototype (single channel)

    • House/3M device gets FDA approval in 1984


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A Brief History (con’t)

  • Clark, University of Melborne (1978)

    • Implant first multi-channel device

    • FDA approval in 1985

  • From then till now:

    • continual improvements have been made in speech processing strategies and electrode design

    • Many patients can use the devices without the aid of lip-reading (even the telephone!)


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Safety Considerations

  • Biomaterials:

    • with the proper choice of materials there is no infection, just a minor fibrous sheath around the implant.

  • Electrode Insertion trauma:

    • factors: surgical technique, dimensions, array’s mechanical properties

    • If damage occurs to basilar membrane and dendrites, could lead to retrograde deterioration. However, are few and far between in most sensorineural hearing loss cases.

    • For most part damage is minimal.

  • Chronic Electrical Stimulation

    • Platinum electrodes: virtually no corrosion or depletion

    • Doesn’t destroy AN, in fact can help keep auditory nerve and cells in cochlear nucleus healthy (Leake et al 1992)

    • impedances and thresholds stabilize several days post implant


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    FDA

    approved

    Current Facts About Cochlear Implants

    • Quick Facts:

      • candidacy: severe-to-profound sensorineural deafness

      • ~70,000 recipients worldwide (~21,000 in the U.S.) *

      • 50% children (12 mo-17 years); 50% adults *

      • Manufacturers:

        • Cochlear Corporation: NucleusTM

        • Advanced Bionics: ClarionTM

        • Med-EL: Combi-40+TM

        • AllHear: AllHearTM single channel

        • Antwerp Bionic Systems: LauraTM (now owned by Cochlear)

        • MXM Laboratories: DigisonicTM

    Cochlear Corporation: NucleusTM

    * FDA survey of venders 11/2001

    http://www.nidcd.nih.gov/health/pubs_hb/coch.htm#c

    (The University of Melbourne)


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    http://www.allhear.com/

    • Company founded by Dr. House

    • Shorter insertion; claims to retain residual hearing in implanted ear

    • Single stimulation channel

    • Not yet approved for sale in United States


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    Cochlear Corporation

    Speech Processors

    Contour

    • Company created out of Greame Clark’s work at the University of Melbourne, Australia

    • First FDA approved multichannel devices

    • 22 channels available for stimulation


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    Advanced Bionics

    The Clarion II Implant

    • Based on work conducted at UCSF

    • Only American Company

    • 16 channels with 16 individual current drivers


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    Med-El Corporation

    Processors

    Combi 40/40+ Implant

    • Headquarters in Austria

    • case for less signal loss and power consumption

    • 12 channels of stimulation


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    Block Diagram for Typical Cochlear Implant System

    Skin

    Transmission

    Link

    External Components

    Internal Components


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    The Speech Signal

    “Never touch a snake with your bare hands.”


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    Progression of Speech Processing Strategies


    Speech processing l.jpg

    Speech Processing

    Sound Input

    Electrical Stimulation


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    Cochlear Frequency Tuning

    The cochlea is arranged such that different regions of the cochlea correspond to different pitches.

    Multichannel cochlear implants take advantage of this fact to encode different frequencies in the speech signal.


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    Cochlear Electrodes

    Cochlear Corporation’s Nucleus Electrode

    Cochlea

    Cochlear

    Electrode

    Auditory

    Nerve


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    What might cochlear implants sound like?

    • Cochlear implant simulations:

      • Single channel

      • 2 channels

      • 3 channels

      • 4 channels

      • 6 channels

      • 8 channels

    (created from Bob Shannon and Philip Lizou’s model)


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    Dorman 2002


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    Factors Effecting Cochlear Implant Performance

    • Duration of deafness

    • Age of onset of deafness

    • Age at implantation

    • Duration of cochlear implant use

    • Other:

      • Number of remaining auditory nerve fibers

      • Electrode placement and insertion depth

      • Dynamic range


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    Future Research Directions

    • Better understanding of fundamental mechanisms

    • Better speech processing algorithms

    • Improved enjoyment of music

    • Electrode design improvements

    • Objective fitting for young children

    • Aesthetics (smaller, totally implantable)


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    Cochlear Implant Research Team

    • Requires integration of many disciplines:

      • Bioengineering

      • Physiology

      • Otolaryngology

      • Speech Science

      • Signal Processing


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