Download OtoAcoustic Emissions (OAE`s)

OtoAcoustic Emissions (OAE’s)
Phenomenon and applications in audiological diagnostics
Measurement procedures
TEOAE and DPOAE
Physiological backgound, functional models

Acknowledgment: several illustrations and diagrams are taken from a
tutorial presentation of Prof. Sebastian Hoth, Heidelberg
Otoacoustic emissions (Dillier:
lecture Medical Acoustics)
Differentiation and quantification
of hearing disorders
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Advantages of OAE
measurement in audiology
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
Objective response
Response specific for cochlea
Sensitive test
Short test procedure
Only passive cooperation required
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Clinical applications
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Detection of hearing disorder (newborn
screening, babies, children, adults with
suspected aggravation, functional hearing
loss)
Monitoring of cochlear function (ototoxic
drugs, noise, degenerative processes,
intraoperative monitoring)
Audiological differential diagnostics: specific
for cochlear lesions
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Types of otoacoustic
emissions
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Spontaneous otoacoustic emissions
(SOAE)
Transitory evoked otoacoustic emissions
(TEOAE)
Distortion product emissions (DPOAE)
Stimulus frequency emissions (SFOAE)
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Otoacoustic emissions (OAE)
Spontaneous
otoacoustic
emissions
(SOAE)
Evoked otoacoustic emissions (EOAE)
Poststimulatory OAE
Transitory
evoked OAE
(TEOAE)
Perstimulatory OAE
Stimulus frequency
Otoacoustic
otoacoustic emissions distortion products
(SFOAE)
(DPOAE)
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Otoacoustic emissions
Measurement equipment for
OAE recordings
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Th. Janssen, in
Praxis der
Audiometrie
(Lehnhardt &
Laszig, 2000)
Principle of evoked otoacoustic
emission measurements (EOAE)
Stimulus
Response
Amplitude
Amplitude
Frequency
Time
TEOAE
Delayed OAE
DPOAE
Transitory Evoked OtoAcoustic Emissions
Distortion products
Distortion Product OtoAcoustic Emissions
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
TEOAE: Transitory (short stimulus, e.g. click)
Evoked OtoAcoustic Emissions
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
OAE: verification/optimization of stimulus/measurement conditions
1. Probe
Cerumen
Patency?
Orientation
Leakage
Stability
2. Stimulus
Level
Ear canal response
Remote from tympanic membrane
3. Environment
Ambient noise
Sound attenuation
Room acoustics
Ear plugs
4. Patient
Respiration
Movements
Cables
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Probe related sources of error
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Th. Janssen, in
Praxis der
Audiometrie
(Lehnhardt &
Laszig, 2000)
Improvement of signal/noise relation by 3-fold summation:
Emission
Noise
Otoacoustic emissions (Dillier:
lecture Medical Acoustics)
3-fold test signal amplitude
1,7-fold
noise signal amplitude
SNR improvement is only dependent on number
of averages (n):
SNR improvement (Gain G):
G = 20 ⋅ log
(c ⋅ n ) (c N ⋅ n )
A (n) AN (n)
S N ( n)
n
= 20 ⋅ log S
= 20 ⋅ log s
= 20 ⋅ log
= 10 ⋅ log n
S N (1)
AS (1) Otoacoustic
AN (1) emissions (Dillier: lecture Medical
cS cAcoustics)
N
n
TEOAE: documentation of measurement and result
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Properties of
„true“ OAE?
Good measurement
conditions
Stimulus
STABILITY
A - B DIFF
reproducible
response
REPRO > 60%
SNR > 6 dB
Typical response properties:
•
•
•
•
•
Emission amplitude between 0 and 25 dB SPL
Emission duration > 6 ms
Initially fast, later slower oscillations
Amplitude decreases with increasing delay
Amplitude decreases for
higher
frequencies
Otoacoustic
emissions (Dillier:
lecture Medical Acoustics)
Polarity averaging and Binomial statistics:
What is the percentage of a positive amplitude at a fixed
temporal interval of a random signal?
Binomial distribution:
Polarity average
Meas. signal
with
n>5: Gaussian distribution
Polarity average
Meas. signal
with
and
If the polarity average reaches a
value of α n, the signal is probably
not a random process (sig. level 1-α)
Polarity average
Time
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Output (linear)
Amplitude
Nonlinearity and distortion
Time
Original signal
Linear Amplification
Intensity
Input (linear)
Nonlinear amplification
Additional frequencies
Frequency
Schematic diagram
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Effect of cubic terms in the transfer function
Input u1(t)
Nonlinear system
u1 (t ) = c(sin ω1t + sin ω 2t )
Output u2(t)
u2 (t ) = a1u1 (t ) + a2u12 (t ) + a3u13 (t ) + ...
Quadratic distortions:
u12 (t ) = ... cos(ω 2 − ω1 )t + sin 2ω1t + cos(ω1 + ω 2 )t + sin 2ω 2t
Cubic distortions:
u13 (t ) = ... sin( 2ω 2 − ω1 )t + sin( 2ω1 − ω 2 )t + terms with
„Distortion product“
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
3ω1
2ω1 + ω 2
2ω 2 + ω1
3ω 2
Equipment to measure distortion
products (DPOAE’s)
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Th. Janssen, in
Praxis der
Audiometrie
(Lehnhardt &
Laszig, 2000)
Stimulation using two sinewaves:
Superposition of the primary travelling waves and origin of
distortion products
stimulus f1
L1 = 70 dB SPL
stimulus f2 = 1.2 * f1
L2 = 70 dB SPL
DP 2f1-f2
Base
f2
Apex
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Stimulation using two sinewaves:
Superposition of travelling waves
f1
f2
Base
Apex
f2 f1
Base
Apex
Overlap: maximum very close to f2
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Spectrum
of DPOAEsignal
Th. Janssen, in
Praxis der
Audiometrie
(Lehnhardt &
Laszig, 2000)
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Audiological interpretation of OAE:
OAE‘s are results of the active cochlear
amplification
The more effective this amplification is...
1.
... the more sensitive the hearing
2.
... the larger the emissions
The OAE amplitude is inversely
proportional to the hearing threshold
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
TEOAE or DPOAE?
Advantages of TEOAE
Advantages of DPOAE
Smaller probe
Less measurement noise
Up to 30 dB hearing
loss
Up to 50 dB hearing loss
Technical artefacts
relatively ease to avoid
Automatic interpretation
Suitable for screening
Systematic inner ear diagnostics
If possible both TEOAE and DPOAE!
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
TEOAE-Measurement at day 2 or 3
„pass“
„refer“
repeat
„refer“
ABR
etc.
„pass“
HI or
CI
Ok
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
DPOAE Screening device
(BioLogic)
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
OAE-Echoscreen (Mack GmbH)
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
OAE Screener Echocheck/Echosensor
(Otodynamics Ltd)
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
GSI 60 DPOAE (Grason Stadler)
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
What does an alerting screening result mean?
development)
Hearing loss prevalence (language development)......:
3 : 1000
Sensitivity
Sensitivity..........................................................
: 100 %
Specifity
Specifity.............................................................
: 92 %
What is the probability that a child with positive screening
result at the first OAE test session has indeed a hearing
loss?
Only in 3 out of 1000
children is a hearing disorder
to be expected
Out of 1000 tested normal hearing
children 80 will show an alerting
screening result
3 / 83 = 0,0361
Positive predictive value.......................................
value
: 3,61 %
According to T. Steffens, Regensburg
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Nonlinear cochlear mechanics:
Sensitivity and frequency selectivity at low stimulation levels
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Johnstone BM, Patuzzi R, Yates GK (1986) Basilar membrane measurements and the travelling wave. Hear Res 22: 147-153
Structure and function of outer hair cells
Tectorial membrane
Fast motility: transversal
force on the hair bundle.
Active amplification?
K+
Cuticular plate
Slow motility: longitudinal
force under efferent control.
Adaptation at high levels?
Electrical tuning
Deiters cells
efferent
afferent
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
After Kim 1986
Cochlear Micromechanics
Amplification and sharpening of basilar
membrane vibrations through
• nonlinearity
• electromotility of outer hair cells
amplification
feedback
Preyer 1996
nonlinearity
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Cochlear sound processing and generation of OAE
Threshold 0 dB
Threshold ~ 50 dB
Otoacoustic emissions (Dillier: lecture Medical Acoustics)
Active filter mechanisms