Presentation given at Cochlear Technology Centre (Mechelen, Belgium) on 13th September, 2012. In the presentation, I gave an overview of the work carried out at the Laboratory of Biomedical Physics (University of Antwerp, Belgium) that is interesting for the company Cochlear. Presentation given for the Cochlear Technology Centre.

1. Study of middle ear mechanics at the
Lab of Biomedical Physics: an overview
Jef Aernouts
September 13th, 2012

2. BIMEF
• Laboratory of Biomedical Physics
University of Antwerp
- www.ua.ac.be/bimef
• Research topics
- Middle ear mechanics
- Biomechanics of skeletal structures
- FE modeling in biomechanics (e.g. ear, blood vessels)
- Development of opto-electrical setups
(shape, deformation, vibrations)
- Vestibular and human equilibrium research
- Research on motion and space sickness
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3. Outline presentation
• My PhD research
- Tympanic membrane (TM) mechanics
• Other research topics in our group
- Detailed ear morphology through micro-CT
- Middle ear mechanics through FE modeling
- TM mechanics through stroboscopic holography
- OCT to determine TM thickness
- Endoscopic measurement of TM shape
- Middle ear mechanics at low frequencies using X-ray
techniques
- Non-linear distortions in the middle ear
2

4. Outline presentation
• My PhD research
- Tympanic membrane (TM) mechanics
• Other research topics in our group
- Detailed ear morphology through micro-CT
- Middle ear mechanics through FE modeling
- TM mechanics through stroboscopic holography
- OCT to determine TM thickness
- Endoscopic measurement of TM shape
- Middle ear mechanics at low frequencies using X-ray
techniques
- Non-linear distortions in the middle ear
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5. Motivation
• Study of middle ear mechanics:
Finite Element (FE) modeling
4

6. Motivation
• Models very sensitive to inputted tympanic
membrane mechanical properties
• Substantial variability in the literature
Mechanical Properties of the Tympanic Membrane:
Measurement and Modeling
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7. TM mechanical properties
• Human
• TM geometry
- Multi-layered
- Circular and radial
fibers
Homogeneous & Isotropic
• Mechanical properties
- Stiffness (Young’s modulus)
- Damping or viscoelasticity
(Complex modulus)
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8. Pressure regimes
• Quasi-static regime • Acoustic regime
- 0-20 Hz - 20-20000 Hz
- Typically - Typically
50-1000+ Pa 0.02 Pa (60 dB SPL) –
2 Pa (100 dB SPL)
> Strains > Strains
- PT: 1,5% at 500 Pa - PT: 0.001% at 90 dB
- PF: >30% at 500 Pa - PF: 0.0013% at 90 dB
(gerbil) (gerbil)
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9. TM elasticity
• Literature: experiments on cut-out strips
- Erroneous analyses (non-uniform thickness)
- Difficult specimen clamping
• In my work: experiments on intact samples
(in situ)
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10. Human tympanic membrane
• Tympanic membrane pars tensa
- Base diameter: 9 mm
- Apex height: 1,7 mm
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11. Indentation approach
• Needle indentation
- Sinusoidal
- Step relaxation
• Sample
• Moiré measurement
• Inverse FE analysis
(1) TM, (2): force transducer,
(3): piston, (4): LVDT , (5): signal
generator, (6): feedback control unit
• FE models
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12. monitor
camera
vaporizer
sample
mounter
attached
to load
cell
piston that
drives needle
LVDT

13. Results
12

14. TM mechanics at acoustic freqs
In Boston
front view
• Laser Doppler vibro-
metry
- Sounds: 100 Hz –
18 kHz, 80-120 dB
- Umbo velocity
• Stroboscopic holo-
graphy
- Sounds: 0.5 kHz –
19 kHz, 80-120 dB
- Full-field displacement
• Sample
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15. FE model
• FE software: Comsol
• Mesh imported from micro-CT measurements
sound wave
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16. Results
• Tympanic membrane transfer function
- Measured with laser Doppler vibrometry
- Finite element model outcome
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17. Results
• Tympanic membrane full-field displacement
- Measured with stroboscopic holography
- Finite element outcome
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18. Outline presentation
• My PhD research
- Tympanic membrane (TM) mechanics
• Other research topics in our group
- Detailed ear morphology through micro-CT
- Middle ear mechanics through FE modeling
- TM mechanics through stroboscopic holography
- OCT to determine TM thickness
- Endoscopic measurement of TM shape
- Middle ear mechanics at low frequencies using X-ray
techniques
- Non-linear distortions in the middle ear
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19. Middle ear morphology: Why?
• Human
• No complete (both bone & soft tissue) datasets
available
• Important for realism of middle ear (FE) models
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20. Ear morphology
• Histological sections • Micro-CT
C distinction bone <> tissue C non-destructive
D destructive D no soft tissue
D tissue deformation C staining > soft tissue
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21. Human ear micro-CT
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22. Human ear micro-CT
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23. Human ear micro-CT
Resolution: 23 m
(voxel size)
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24. Outline presentation
• My PhD research
- Tympanic membrane (TM) mechanics
• Other research topics in our group
- Detailed ear morphology through micro-CT
- Middle ear mechanics through FE modeling
- TM mechanics through stroboscopic holography
- OCT to determine TM thickness
- Endoscopic measurement of TM shape
- Middle ear mechanics at low frequencies using X-ray
techniques
- Non-linear distortions in the middle ear
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25. Middle ear FE model
• Human micro-CT geometry data imported
• TM material properties from PhD work Aernouts
• Model allows
- Study of middle ear biomechanics
- Study of energy transport on TM
• Update model to
- Study ME implant behavior
- Study ME microphone attachment
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26. Middle ear FE model results
1000 Hz 7000 Hz 16000 Hz
(x8e3) (x3e4) (x2e5)
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27. Middle ear FE model results
1000 Hz 7000 Hz 16000 Hz
(x2e4) (x3e5) (x3e6)
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28. Outline presentation
• My PhD research
- Tympanic membrane (TM) mechanics
• Other research topics in our group
- Detailed ear morphology through micro-CT
- Middle ear mechanics through FE modeling
- TM mechanics through stroboscopic holography
- OCT to determine TM thickness
- Endoscopic measurement of TM shape
- Middle ear mechanics at low frequencies using X-ray
techniques
- Non-linear distortions in the middle ear
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29. Holography
• Principle
• Digital
holography
- CCD
- Virtual reconstruction:
hologram before and
after > deformation
CCD
28

30. Stroboscopic holography
• Shutter laser beam/
pulsed laser on specific
phases
• Both magnitude and phase
of vibration pattern
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31. Setup
NOW FUTURE
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32. Results rubber sheet
363 Hz at 75 dB
1040 Hz at 85 dB
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33. Outline presentation
• My PhD research
- Tympanic membrane (TM) mechanics
• Other research topics in our group
- Detailed ear morphology through micro-CT
- Middle ear mechanics through FE modeling
- TM mechanics through stroboscopic holography
- OCT to determine TM thickness
- Endoscopic measurement of TM shape
- Middle ear mechanics at low frequencies using X-ray
techniques
- Non-linear distortions in the middle ear
32

34. TM thickness: Why?
• There is no literature on full-field human
tympanic membrane thickness
• The thickness distribution is an important input
parameter in middle ear (FE) models
33

35. Optical Coherence Tomography
• Imaging technique
• Broadband infrared
light source
> short coherence
> length
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36. OCT results (human)
OCT image dataset image correction
+ segmentation
surface generation
(triangulation)
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37. Outline presentation
• My PhD research
- Tympanic membrane (TM) mechanics
• Other research topics in our group
- Detailed ear morphology through micro-CT
- Middle ear mechanics through FE modeling
- TM mechanics through stroboscopic holography
- OCT to determine TM thickness
- Endoscopic measurement of TM shape
- Middle ear mechanics at low frequencies using X-ray
techniques
- Non-linear distortions in the middle ear
36

38. Oto-endoscopy
Typically used in ENT clinics
C diagnose
D no quantitative data
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39. Endoscopic moiré
• Moiré profilometry
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40. Endoscopic moiré
• Moiré profilometry
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41. Endoscopic moiré
• Endoscopic moiré profilometry
> In vivo tool
> Quantitative
> Simultaneous
> with tympanometry:
> locate weak spots
> Problem:
> lens distortions
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42. Real-time distortion correction
• Endoscopic images contain barrel distortion
correction
41

43. Real-time distortion correction
• Programmed on a GPU
• Real-time (no post-processing)
42

44. Outline presentation
• My PhD research
- Tympanic membrane (TM) mechanics
• Other research topics in our group
- Detailed ear morphology through micro-CT
- Middle ear mechanics through FE modeling
- TM mechanics through stroboscopic holography
- OCT to determine TM thickness
- Endoscopic measurement of TM shape
- Middle ear mechanics at low frequencies using
X-ray techniques
- Non-linear distortions in the middle ear
43

45. Idea
• X-ray imaging
C no need for optical access as in the case of LDV
C measurements on a closed middle ear cavity
D rather low resolution compared to LDV
• Stereoscopy
- Gain 3D information by taking multiple shots at various
angles
- Time information from grayscale analysis
3D motion of non-transparent objects
44

46. X-ray stereoscopy on rabbit ME
• Rabbit middle ear
• Quasi-static pressures
- Freqs: 0,5–50 Hz
- Amplitudes: 0,25–1 kPa
• Useful for study of a: X-ray point source, b: detector,
- middle ear implants: c: pressure generator, d: specimen
holder, f: specimen
loosening piston attachment
- retraction pockets
45

47. X-ray stereoscopy results
Integrated X-ray shadow
image of 2 Tungsten beads
at 1 Hz with 1 kPa pressure
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48. Outline presentation
• My PhD research
- Tympanic membrane (TM) mechanics
• Other research topics in our group
- Detailed ear morphology through micro-CT
- Middle ear mechanics through FE modeling
- TM mechanics through stroboscopic holography
- OCT to determine TM thickness
- Endoscopic measurement of TM shape
- Middle ear mechanics at low frequencies using X-ray
techniques
- Non-linear distortions in the middle ear
47

49. Non-linearity in the ME
• It is generally believed that the human middle
ear is a linear system up till 130 dB (SPL)
• Strong non-linearity in the quasi-static regime
• Small non-linearity in acoustic regime at high
sound pressure levels?
- Important for e.g. hearing aids and implantable
microphones that use high sound pressure levels
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50. Detection method
• Input signal: multisine
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51. Detection method
• Linear output
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52. Detection method
• Non-linear output
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53. Measurement setup
• Measurements on the gerbil middle ear
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54. Results non-linear distortions
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55. Thanks...
... for your attention!
More information and published articles at
www.ua.ac.be/bimef
Contact:
Jef.Aernouts@gmail.com
Joris.Dirckx@ua.ac.be
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