Cochlear Prostheses: An Introduction - PowerPoint Presentation

Slide1

Cochlear Prostheses: An Introduction

2011.4.5

배장

표Slide2

The second most successful neural prostheses

The first is cardiac pacemakers

Auditory physiology, psychophysics, material science, electric engineering and eletronic technologyvideo

IntroductionSlide3

Cochlear Implant History

Pre-1960’s

- beginning studies of electrical stimulation on humans

1960’s

- active research of electrical stimulation in human ears

1970’s - first wearable implants designed for long-term stimulation1980’s - commercial development of the cochlear implant device beganSlide4

1985

- United States Food & Drug Administration (FDA) granted the first approval for implantation in adults

1990

- FDA granted approval for cochlear implants in children

Today

- cochlear implantation is a safe and effective medical procedure for individuals who are severely to profoundly deaf with minimal benefits from conventional hearing aids

http://216.133.14.145/gettingstarted/history.htm

Cochlear Implant HistorySlide5

귀의 구조와 기능Slide6

middle ear -> 60%(transmission) + 40%(reflection)

EX) Cat ->94%(transmission) + 6%(reflection)

중이Slide7

The subjective attribute of tones that correlates most closely with the physical dimension of frequency

Pitch can affect loudness and vice versa. For example, increasing the intensity of a sound not only increases the loudness

Pitch and cochlearSlide8

내이 또는

와우

내이 또는

와우

(달팽이관)

-

달팽이처럼 생겼으며 유체

(

림프액

)

로 채워져 있음

-

여기에는 유모세포라고 하는 민감한 감각세포들이

있음

-

각 세포 끝에 미세한

머리카락같은

모양으로 붙어

있음

- 유모세포는 소리를 듣는 데에 있어 아주 중요한 역할을 담당 Slide9

Acoustic signal : ear canal->middle ear->cochlea

the mechanical energy =>electric spikes,

in cochlea, on auditory nerve fibersHigh pitch tone -> base, low pitch tone -> cochlear apex

Mechanism of normal hearingSlide10

Damaged hair cellsSlide11

First: loss of hair cells and nerve fibers => classic hearing loss

Second: few hair cells and a significant number of auditory nerve degenerated => cochlear implant

Impaired peripheral auditory systemSlide12

여러 가지 순음에 대하여 우리가 들을 수 있는 가장 작은 소리에서

큰 소리까지를 주파수와 음압으로 나타낸 것

가청 영역도Slide13

<25

데시벨

26~40

데시벨

41~55

데시벨

56~70

데시벨

71~90 데시벨

>90

데시벨

정상청력

normal

경도 난청

mild

중등도 난청

moderate

중등도 고난청

moderately severe

고도 난청

severe

농

(

聾

) deaf

청력장애의 정도Slide14

외이나

중이 내에 생긴 문제

로서 소리가 귀 속으로 전달되는 데에 있어 방해요소가

되어 발생

.

고막과 이소골이 정상적으로 진동하지 않아 소리를 듣기가 더욱 힘들어짐

외이나

중이에 생긴 문제로 인해 소리가 귀 안으로 들어가는 데에 방해요소가

되어

전음성

난청이 초래

전음성

난청은 보통 경도 중도

,

다시 말해

60~70

데시벨 정도까지의 난청을 말함

전음성

난청은 일시적으로 발생 및 소멸

난청원인에 따라 약물치료 또는 수술로 치유 가능

보청기 착용에 의해 치료 가능

전음성

난청Slide15

내이 또는

와우

(

달팽이관

)

에 생긴 문제 로 발생.

문제가 생기면 감각신경성 난청을 초래

난청 정도는 경도

,

중도

,

고도

,

심도

,

심지어 전농

(

완전실청

)

까지 다양

감각신경성 난청은 대부분 영구적

내이 부분의 외과적 치료는 현재로서는 불가능하나 그 원인에 따라 어떤

경우에는 약물치료가 도움이 되는 경우도 있음

경도

,

중도

,

고도 난청자에게는 보청기가 도움이 될 수 있음

최고출력의 보청기를 사용하고서도 충분한 어음정보를 얻을 수 없는 심도

,

고도

,

전농자들에겐

인공와우가

매우 효과적인 선택대안이 될 수 있음

감각 신경성 난청Slide16

신경경로에서 발생한 문제

.

청신경이 손상을 입거나 유실되어 청각신호를 뇌에

전달하지 못하는 것

극히 드문 경우로서 청신경이 아예 없거나 손상을 입으면 신경성 난청이 발생

청신경이 충분한 소리정보를 뇌에 공급하지 못하므로 일반 보청기는

거의 도움이 안됨

청신경이

제기능을

하지 못하면

인공와우도

도움이 되지 못함

어떤 경우에는

뇌간이식

(auditory brainstem implant)

이 도움이 되기도 함

신경성 난청Slide17

Acoustic sound => electric signal by sound processor

Receiver/stimulator unit is implanted in the bone under the skin above the patient’s ear

Communication by RF16~24 electrode usedLow pitch tone => apical electrode =>apical nerve fibers

Performance is not satisfactory

Cochlear implant systemSlide18

there are three major CI manufacturers:  Cochlear (Australia), Advanced Bionics (USA), and Med-El (Austria).

Cochlear implant systemSlide19

Upper: 36 patients implanted with recent device

Normal hearing 100%

Better than 70% => fluent conversation without lipreadingLower: five poorest performing patients

performanceSlide20

Signal

Processing

Nerve

Excitation

Brain

M

Nerve Fibers

N

Stimulation Channels

Basal

Apical

Information Reduced or Altered

Information Reduced or Altered

Information Complete

Information loss

Acoustic signal( ) => stimulation signal( ) by Cochlear system

=> Modification of signal processing for improvement

the process of nerve excitation limits information transfer

how the brain interprets.

reversed channel mapping( low

freqencey

<-> high frequency) => difficult interpretationSlide21

100~4000Hz signal

Automatic gain control=>balance between the electrode output and outside sound

If output is combined and normal person hear that sound, 100 score on the single syllable word test appears. Convert current source => less noise

Improving performance(signal processing)Slide22

At the time marked by the vertical line, channel II(-), channel III(+)

Distance between Channel II and III : 3mm, highly conductive fluid(70

Ω-cm) Potential summation across electrodes produces a very small overall stimulus

Distortion of the desired magnitude of stimulation and the pattern of neural activity desired

Improving performance(nerve excitation)Slide23

Minimize potential summation across electrodes

Envelope detection by rectification followed by low-pass filtering( cut-off frequency 200~400Hz) or

quadrature detectionEnvelop is modulated with a carrier( biphasic pulse train: 2000 pulses per second)

2kpps => the duration of the carriers’ biphasic pulses is 125 us to interleave four carriers

reduce distortion from field interactions

But loss of the fine structure of signal Continuous interleaved stimulation(CIS) sound processing strategySlide24

12 month wearer of original sound processing device => CIS device

Need time to adapt to new device.

Continuous interleaved stimulation(CIS) sound processing strategySlide25

What is involved in a

CI follow-up?

For Adults:

- weekly adjustments of the MAP and communication therapy for the first month.

- treatment focuses on auditory training, speech reading, music, telephone use & communication strategies.Slide26

What is involved in a

CI follow-up?

For children:

- after the initial 3 month period, children are usually seen every 3 months for the first year and every 6 months for the second and third years. Thereafter, they are seen annually.

- MAP is closely monitored.

http://depts.washington.edu

MAP

– specifications of threshold,

suprathreshold

, and frequency by which the speech processor of a cochlear implant processes the speech signal and delivers it in electrical form to the electrodes in the electrode arraySlide27

Restore the fine time structure discarded by the CIS processing strategy

Bilateral implants : two ears

Localization of sound sources and better speech receptionCoordination of electric stimulation in one ear and acoustic input in the same or unimplanted

ear

Physical devices more functional and esthetically pleasing

Internal batteriesFutureSlide28

Design for a simplified Cochlear Implant System

from

서울대 전기공학부 김성준 교수님 그룹Slide29

Simplified cochlear implant system,

개발 도상국 대상

, 싼 가격8 channel, CIS strategyDSP chip, FFT for filteringData communication by pulse width modulation(PWM) encoding and amplitude shift keying(ASK),

양방향 통신 가능

Titanium package, hermetically sealed

16 ball-shaped stimulating contactssystem overviewSlide30

System overviewSlide31

Signal processingSlide32

Communication protocolSlide33

Switch on/off

와

duration 조정해서 pulse 모양과

mode

조정 가능

Monopolar(16 ch),bipolar(8 ch) Current source는 capacitor에 남은 charge를 방전시키기 위해stimulatorSlide34

CIS(continuous interleaved signal)