Study of middle ear mechanics at theLab of Biomedical Physics: an overviewJef AernoutsSeptember 13th, 2012
BIMEF• Laboratory of Biomedical Physics  University of Antwerp  - www.ua.ac.be/bimef• Research topics  - Middle ear mechan...
Outline presentation• My PhD research  - Tympanic membrane (TM) mechanics• Other research topics in our group  - Detailed ...
Outline presentation• My PhD research  - Tympanic membrane (TM) mechanics• Other research topics in our group  - Detailed ...
Motivation• Study of middle ear mechanics:  Finite Element (FE) modeling                                   4
Motivation• Models very sensitive to inputted tympanic  membrane mechanical properties• Substantial variability in the lit...
TM mechanical properties• Human• TM geometry   - Multi-layered   - Circular and radial     fibersHomogeneous & Isotropic• ...
Pressure regimes• Quasi-static regime    • Acoustic regime  - 0-20 Hz                - 20-20000 Hz  - Typically           ...
TM elasticity• Literature: experiments on cut-out strips  - Erroneous analyses (non-uniform thickness)  - Difficult specim...
Human tympanic membrane• Tympanic membrane pars tensa  - Base diameter: 9 mm  - Apex height: 1,7 mm                       ...
Indentation approach• Needle indentation  - Sinusoidal  - Step relaxation• Sample• Moiré measurement• Inverse FE analysis ...
monitor                          camera                          vaporizersamplemounterattachedto loadcell                ...
Results          12
TM mechanics at acoustic freqs               In Boston                              front view• Laser Doppler vibro-  metr...
FE model• FE software: Comsol• Mesh imported from micro-CT measurements                    sound wave                     ...
Results• Tympanic membrane transfer function  - Measured with laser Doppler vibrometry  - Finite element model outcome    ...
Results• Tympanic membrane full-field displacement  - Measured with stroboscopic holography  - Finite element outcome     ...
Outline presentation• My PhD research  - Tympanic membrane (TM) mechanics• Other research topics in our group  - Detailed ...
Middle ear morphology: Why?• Human• No complete (both bone & soft tissue) datasets  available• Important for realism of mi...
Ear morphology• Histological sections        • Micro-CTC distinction bone <> tissue   C non-destructiveD destructive      ...
Human ear micro-CT                     20
Human ear micro-CT                     21
Human ear micro-CT           Resolution: 23 m           (voxel size)                              22
Outline presentation• My PhD research  - Tympanic membrane (TM) mechanics• Other research topics in our group  - Detailed ...
Middle ear FE model• Human micro-CT geometry data imported• TM material properties from PhD work Aernouts• Model allows  -...
Middle ear FE model results1000 Hz     7000 Hz      16000 Hz (x8e3)      (x3e4)       (x2e5)                              ...
Middle ear FE model results1000 Hz     7000 Hz      16000 Hz (x2e4)      (x3e5)       (x3e6)                              ...
Outline presentation• My PhD research  - Tympanic membrane (TM) mechanics• Other research topics in our group  - Detailed ...
Holography• Principle• Digital  holography   - CCD   - Virtual reconstruction:     hologram before and     after > deforma...
Stroboscopic holography• Shutter laser beam/  pulsed laser on specific  phases• Both magnitude and phase  of vibration pat...
SetupNOW           FUTURE                       30
Results rubber sheet363 Hz at 75 dB                  1040 Hz at 85 dB                                     31
Outline presentation• My PhD research  - Tympanic membrane (TM) mechanics• Other research topics in our group  - Detailed ...
TM thickness: Why?• There is no literature on full-field human  tympanic membrane thickness• The thickness distribution is...
Optical Coherence Tomography• Imaging technique• Broadband infrared  light source  > short coherence  > length            ...
OCT results (human)OCT image dataset          image correction                           + segmentation                   ...
Outline presentation• My PhD research  - Tympanic membrane (TM) mechanics• Other research topics in our group  - Detailed ...
Oto-endoscopyTypically used in ENT clinicsC diagnoseD no quantitative data                                37
Endoscopic moiré• Moiré profilometry                               38
Endoscopic moiré• Moiré profilometry                               39
Endoscopic moiré• Endoscopic moiré profilometry                                  >   In vivo tool                         ...
Real-time distortion correction• Endoscopic images contain barrel distortion                     correction               ...
Real-time distortion correction• Programmed on a GPU• Real-time (no post-processing)                                     42
Outline presentation• My PhD research  - Tympanic membrane (TM) mechanics• Other research topics in our group  - Detailed ...
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 r...
X-ray stereoscopy on rabbit ME• Rabbit middle ear• Quasi-static pressures   - Freqs: 0,5–50 Hz   - Amplitudes: 0,25–1 kPa•...
X-ray stereoscopy resultsIntegrated X-ray shadowimage of 2 Tungsten beadsat 1 Hz with 1 kPa pressure                      ...
Outline presentation• My PhD research  - Tympanic membrane (TM) mechanics• Other research topics in our group  - Detailed ...
Non-linearity in the ME• It is generally believed that the human middle  ear is a linear system up till 130 dB (SPL)• Stro...
Detection method• Input signal: multisine                               49
Detection method• Linear output                               50
Detection method• Non-linear output                               51
Measurement setup• Measurements on the gerbil middle ear                                          52
Results non-linear distortions                                 53
Thanks...          ... for your attention!More information and published articles at          www.ua.ac.be/bimef          ...
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Study of middle ear mechanics at the Lab of Biomedical Physics: an overview

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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.

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Study of middle ear mechanics at the Lab of Biomedical Physics: an overview

  1. 1. Study of middle ear mechanics at theLab of Biomedical Physics: an overviewJef AernoutsSeptember 13th, 2012
  2. 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 1
  3. 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. 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 3
  5. 5. Motivation• Study of middle ear mechanics: Finite Element (FE) modeling 4
  6. 6. Motivation• Models very sensitive to inputted tympanic membrane mechanical properties• Substantial variability in the literatureMechanical Properties of the Tympanic Membrane:Measurement and Modeling 5
  7. 7. TM mechanical properties• Human• TM geometry - Multi-layered - Circular and radial fibersHomogeneous & Isotropic• Mechanical properties - Stiffness (Young’s modulus) - Damping or viscoelasticity (Complex modulus) 6
  8. 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) 7
  9. 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) 8
  10. 10. Human tympanic membrane• Tympanic membrane pars tensa - Base diameter: 9 mm - Apex height: 1,7 mm 9
  11. 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 10
  12. 12. monitor camera vaporizersamplemounterattachedto loadcell piston that drives needle LVDT
  13. 13. Results 12
  14. 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 13
  15. 15. FE model• FE software: Comsol• Mesh imported from micro-CT measurements sound wave 14
  16. 16. Results• Tympanic membrane transfer function - Measured with laser Doppler vibrometry - Finite element model outcome 15
  17. 17. Results• Tympanic membrane full-field displacement - Measured with stroboscopic holography - Finite element outcome 16
  18. 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 17
  19. 19. Middle ear morphology: Why?• Human• No complete (both bone & soft tissue) datasets available• Important for realism of middle ear (FE) models 18
  20. 20. Ear morphology• Histological sections • Micro-CTC distinction bone <> tissue C non-destructiveD destructive D no soft tissueD tissue deformation C staining > soft tissue 19
  21. 21. Human ear micro-CT 20
  22. 22. Human ear micro-CT 21
  23. 23. Human ear micro-CT Resolution: 23 m (voxel size) 22
  24. 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 23
  25. 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 24
  26. 26. Middle ear FE model results1000 Hz 7000 Hz 16000 Hz (x8e3) (x3e4) (x2e5) 25
  27. 27. Middle ear FE model results1000 Hz 7000 Hz 16000 Hz (x2e4) (x3e5) (x3e6) 26
  28. 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 27
  29. 29. Holography• Principle• Digital holography - CCD - Virtual reconstruction: hologram before and after > deformation CCD 28
  30. 30. Stroboscopic holography• Shutter laser beam/ pulsed laser on specific phases• Both magnitude and phase of vibration pattern 29
  31. 31. SetupNOW FUTURE 30
  32. 32. Results rubber sheet363 Hz at 75 dB 1040 Hz at 85 dB 31
  33. 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. 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. 35. Optical Coherence Tomography• Imaging technique• Broadband infrared light source > short coherence > length 34
  36. 36. OCT results (human)OCT image dataset image correction + segmentation surface generation (triangulation) 35
  37. 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. 38. Oto-endoscopyTypically used in ENT clinicsC diagnoseD no quantitative data 37
  39. 39. Endoscopic moiré• Moiré profilometry 38
  40. 40. Endoscopic moiré• Moiré profilometry 39
  41. 41. Endoscopic moiré• Endoscopic moiré profilometry > In vivo tool > Quantitative > Simultaneous > with tympanometry: > locate weak spots > Problem: > lens distortions 40
  42. 42. Real-time distortion correction• Endoscopic images contain barrel distortion correction 41
  43. 43. Real-time distortion correction• Programmed on a GPU• Real-time (no post-processing) 42
  44. 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. 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. 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. 47. X-ray stereoscopy resultsIntegrated X-ray shadowimage of 2 Tungsten beadsat 1 Hz with 1 kPa pressure 46
  48. 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. 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 48
  50. 50. Detection method• Input signal: multisine 49
  51. 51. Detection method• Linear output 50
  52. 52. Detection method• Non-linear output 51
  53. 53. Measurement setup• Measurements on the gerbil middle ear 52
  54. 54. Results non-linear distortions 53
  55. 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 54

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