Powerpoint presentation of my public PhD defense, held on September 24, 2012. Title: Mechanical properties of the tympanic membrane - Measurement and modeling

1. Mechanical Properties of the Tympanic
Membrane: Measurement and Modeling
Jef Aernouts
Laboratory of Biomedical Physics (BIMEF)
University of Antwerp
PhD defense
September 24th, 2012

2. A PhD study
• PhD: Doctor of Philosophy
- “philosophy” = “love of wisdom”
• PhD in Physics
- “to understand the behavior of natural phenomena…”
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3. A PhD study
• PhD: Doctor of Philosophy
- “philosophy” = “love of wisdom”
• PhD in Physics
- “to understand the behavior of natural phenomena…
…and to use this knowledge for new technologies”
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4. Mechanical Properties of the Tympanic
Membrane: Measurement and Modeling
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5. Mechanical Properties of the Tympanic
Membrane: Measurement and Modeling
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6. The human ear
tympanic
membrane
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7. Middle ear & tympanic membrane
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8. Function of the ear
Convert sound (20-20000 Hz) > nerve activity in our brain
What is role middle ear?
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9. Role of the middle ear
Impedance matching
air
between air & fluid fluid
?
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10. Middle ear impedance matching
1. Area ratio
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11. Middle ear impedance matching
1. Area ratio
2. Lever action
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12. Middle ear impedance matching
1. Area ratio
2. Lever action
3. „Buckling effect‟
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13. Mechanical Properties of the Tympanic
Membrane: Measurement and Modeling
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14. Mechanics
• “Behavior of solids when subjected to forces”
Elasticity
linear
visco-elastic
stress
F/A
non-linear
steel rubber biological strain
tissue l/l
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15. Mechanics
• “Behavior of solids when subjected to forces”
Vibrational mechanics
100 Hz
(deformation x1e4)
5000 Hz
(deformation x4e6)
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16. Why study TM mechanics?
• Middle ear finite element modeling
tympanic membrane!
normal
(Aerts J, Aernouts J. 2012) reconstructed
diseased (Kelly et al., 2003)
(Gan et al., 2009)
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17. Mechanical Properties of the Tympanic
Membrane: Measurement and Modeling
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18. Mechanical Properties of the Tympanic
Membrane: Measurement and Modeling
1. Validation measurements and modeling
2. Gerbil tympanic membrane pars tensa elasticity
3. Gerbil tympanic membrane pars flaccida elasticity
4. Human tympanic membrane elasticity
5. Human tympanic membrane vibrations
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19. Mechanical Properties of the Tympanic
Membrane: Measurement and Modeling
1. Validation measurements and modeling
2. Gerbil tympanic membrane pars tensa elasticity
3. Gerbil tympanic membrane pars flaccida elasticity
4. Human tympanic membrane elasticity
5. Human tympanic membrane vibrations
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20. Mechanical Properties of the Tympanic
Membrane: Measurement and Modeling
1. Validation measurements and modeling
2. Gerbil tympanic membrane pars tensa elasticity
3. Gerbil tympanic membrane pars flaccida elasticity
4. Human tympanic membrane elasticity
5. Human tympanic membrane vibrations
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21. Human tympanic membrane
- Base diameter: 9 mm
- Apex height: 1.7 mm
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22. TM elasticity
• Literature: experiments on cut-out strips
- Erroneous analyses (non-uniform thickness)
- Difficult specimen clamping
• In my work: experiments on intact samples
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23. Needle indentation
• Approach
- Apply indentations
- Measure forces
(1) TM, (2): force transducer,
(3): piston, (4): LVDT , (5): signal
generator, (6): feedback control unit
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24. Needle indentation
• Approach
- Apply indentations
- Measure forces
• Sample preparation
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25. Needle indentation
• Approach
- Apply indentations
- Measure forces
• Sample preparation
• Results
- Quasi-static
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26. Needle indentation
• Approach
- Apply indentations
- Measure forces
• Sample preparation
• Results
- Quasi-static
- Step
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27. monitor
camera
vaporizer
sample
mounter
attached
to load
cell
piston that
drives needle
LVDT

28. Shape measurement
• Moiré profilometry
Buytaert JAN, Dirckx JJJ. Phase-shifting Moiré topography using optical demodulation
on liquid crystal matrices. Optics and Lasers in Engineering. 2010;48(2):172–181.
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29. Shape measurement
• Moiré profilometry
Buytaert JAN, Dirckx JJJ. Phase-shifting Moiré topography using optical demodulation
on liquid crystal matrices. Optics and Lasers in Engineering. 2010;48(2):172–181.
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30. Finite element model
1. Import geometry
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31. Finite element model
1. Import geometry
2. Mesh geometry
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32. Finite element model
In rest
1. Import geometry
2. Mesh geometry
3. Apply loadings &
boundary conditions Indented
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33. Finite element model
1. Import geometry
2. Mesh geometry
3. Apply loadings &
boundary conditions
4. Quasi-static stiffness:
E = (2.9±1.3) MPa
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34. Visco-elastic properties
• Relaxation function in time domain
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35. Visco-elastic properties
• Relaxation function in time domain
 frequency domain
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36. Mechanical Properties of the Tympanic
Membrane: Measurement and Modeling
1. Validation measurements and modeling
2. Gerbil tympanic membrane pars tensa elasticity
3. Gerbil tympanic membrane pars flaccida elasticity
4. Human tympanic membrane elasticity
5. Human tympanic membrane vibrations
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37. Work at Boston
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38. TM mechanics at acoustic freqs
• Sample
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39. TM mechanics at acoustic freqs
front view
• Sample
• Laser Doppler vibrometry
- Sounds: 100 Hz –
18 kHz, 80-120 dB
- Umbo velocity
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40. TM mechanics at acoustic freqs
• Sample
• Laser Doppler vibrometry
- Sounds: 100 Hz –
18 kHz, 80-120 dB
- Umbo velocity
• Stroboscopic holography
- Sounds: 0.5 kHz –
19 kHz, 80-120 dB
- Full-field displacement
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41. Holography
• Principle
• Digital
holography
- CCD
- Virtual reconstruction:
hologram before and
after > deformation
CCD
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42. Stroboscopic holography
• Shutter laser beam/
pulsed laser on specific
phases
• Both magnitude and phase
of vibration pattern
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43. probe microphone
speaker
holography setup
sample
camera

44. FE model
• Geometry (from micro-CT)
(Aerts Johan, 2012)
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45. FE model
• Geometry (from micro-CT)
• Boundary conditions & Loadings
sound wave
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46. TM transfer function
- Measured with laser Doppler vibrometry:
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47. TM transfer function
- Measured with laser Doppler vibrometry:
- Finite element model outcome
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48. TM full-field displacement
- Measured with stroboscopic holography:
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49. TM full-field displacement
- Measured with stroboscopic holography:
- Finite element outcome
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50. TM wave motion
1000 Hz
(deformation x6e3)
7000 Hz
(deformation x1e5)
16000 Hz
(deformation x8e5)
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51. TM curvature
• Cochlear load at umbo (tip malleus)
• Natural curved versus artificially flat
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52. TM curvature
800 Hz – 4 kHz:
• Umbo velocity response 17.5 dB difference
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53. General conclusion
• Indentation approach
- Quasi-static regime (0.001 Hz – 3 Hz)
- Elastic characterization pars tensa
• Static inflation experiments
- Elastic characterization pars flaccida
• Stroboscopic holography
- Acoustic regime (20 Hz – 20 kHz)
- Vibrational properties tympanic membrane
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54. Thanks for your attention!
• Questions? I‟m all ears…
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