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2011.4.5 배장표 The second most successful neural prostheses ◦ The first is cardiac pacemakers Auditory physiology, psychophysics, material science, electric engineering and eletronic technology video 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 stimulation 1980’s - commercial development of the cochlear implant device began Cochlear Implant History 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.ht m • middle ear -> 60%(transmission) + 40%(reflection) EX) Cat ->94%(transmission) + 6%(reflection) 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 • 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 Acoustic signal : ear canal->middle ear>cochlea the mechanical energy =>electric spikes, in cochlea, on auditory nerve fibers High pitch tone -> base, low pitch tone -> cochlear apex 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 가청 영역도 여러 가지 순음에 대하여 우리가 들을 수 있는 가장 작은 소리에서 큰 소리까지를 주파수와 음압으로 나타낸 것 청력장애의 정도 <25 데시벨 정상청력 normal 26~40데시벨 경도 난청 mild 41~55 데시벨 중등도 난청 moderate 56~70 데시벨 중등도 고난청 moderately severe 71~90 데시벨 고도 난청 severe >90 데시벨 농(聾) deaf 전음성 난청 외이나 중이 내에 생긴 문제로서 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 감각 신경성 난청 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 신경성 난청 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 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 RF 16~24 electrode used Low pitch tone => apical electrode =>apical nerve fibers Performance is not satisfactory there are three major CI manufacturers: Cochlear (Australia), Advanced Bionics (USA), and Med-El (Austria). Upper: 36 patients implanted with recent device ◦ Normal hearing 100% ◦ Better than 70% => fluent conversation without lipreading Lower: five poorest performing patients • Acoustic signal(s (t ) ) => stimulation signal(ik (s) ) 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 interpretation Informatio n Reduced or Altered Informatio n Reduced or Altered Informatio n Complete Basal iN (s) s (t ) Signal Processing N Stimulatio n Channels Nerve Excitation M Nerve Fibers i1 (t ) Apical Brain 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 At the time marked by the vertical line, channel II(-), channel III(+) Distance between Channel II and III : 3mm, highly conductive fluid(70Ωcm) ◦ Potential summation across electrodes produces a very small overall stimulus Distortion of the desired magnitude of stimulation and the pattern of neural activity desired Minimize potential summation across electrodes Envelope detection by rectification followed by low-pass filtering( cut-off frequency 200~400Hz) or quadrature detection Envelop 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 12 month wearer of original sound processing device => CIS device Need time to adapt to new device. 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. 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 array Restore the fine time structure discarded by the CIS processing strategy Bilateral implants : two ears ◦ Localization of sound sources and better speech reception Coordination of electric stimulation in one ear and acoustic input in the same or unimplanted ear Physical devices more functional and esthetically pleasing Internal batteries Simplified cochlear implant system, 개발 도상 국 대상, 싼 가격 8 channel, CIS strategy DSP chip, FFT for filtering Data communication by pulse width modulation(PWM) encoding and amplitude shift keying(ASK), 양방향 통신 가능 Titanium package, hermetically sealed 16 ball-shaped stimulating contacts Switch on/off와 duration 조정해서 pulse 모양과 mode 조정 가능 ◦ Monopolar(16 ch),bipolar(8 ch) Current source는 capacitor에 남은 charge를 방전시키기 위해