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Cochlear Implants

Cochlear Implants

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Cochlear Implants

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  1. Cochlear Implants Ryan S. Clement, PhD Neural Engineering and Applications Laboratory BioE 200: September 18, 2002

  2. 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

  3. 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/

  4. Sound Transduction Cochlea Hair Cells Cochlear cross-section (single turn) Basilar Membrane Auditory Nerve http://www.iurc.montp.inserm.fr/cric/audition/

  5. OHCs IHCs Sensorineural Hearing Loss • Causes • Heredity • Genetic • Aging process • Ototoxic drugs • Excessive exposure to loud sounds Microscopic view of hair cells.

  6. Electrical Stimulation Can Allow Us to Bypass Damaged Haircells

  7. 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

  8. 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!)

  9. 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

  10. 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)

  11. 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

  12. 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

  13. Advanced Bionics The Clarion II Implant • Based on work conducted at UCSF • Only American Company • 16 channels with 16 individual current drivers

  14. Med-El Corporation Processors Combi 40/40+ Implant • Headquarters in Austria • case for less signal loss and power consumption • 12 channels of stimulation

  15. Block Diagram for Typical Cochlear Implant System Skin Transmission Link External Components Internal Components

  16. The Speech Signal “Never touch a snake with your bare hands.”

  17. Progression of Speech Processing Strategies

  18. Speech Processing Sound Input Electrical Stimulation

  19. 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.

  20. Cochlear Electrodes Cochlear Corporation’s Nucleus Electrode Cochlea Cochlear Electrode Auditory Nerve

  21. 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)

  22. Dorman 2002

  23. 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

  24. 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)

  25. Cochlear Implant Research Team • Requires integration of many disciplines: • Bioengineering • Physiology • Otolaryngology • Speech Science • Signal Processing