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

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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  • 1. Study of middle ear mechanics at theLab of Biomedical Physics: an overviewJef AernoutsSeptember 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 1
  • 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 3
  • 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 literatureMechanical Properties of the Tympanic Membrane:Measurement and Modeling 5
  • 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. 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. 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. Human tympanic membrane• Tympanic membrane pars tensa - Base diameter: 9 mm - Apex height: 1,7 mm 9
  • 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. monitor camera vaporizersamplemounterattachedto loadcell 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 13
  • 15. FE model• FE software: Comsol• Mesh imported from micro-CT measurements sound wave 14
  • 16. Results• Tympanic membrane transfer function - Measured with laser Doppler vibrometry - Finite element model outcome 15
  • 17. Results• Tympanic membrane full-field displacement - Measured with stroboscopic holography - Finite element outcome 16
  • 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. Middle ear morphology: Why?• Human• No complete (both bone & soft tissue) datasets available• Important for realism of middle ear (FE) models 18
  • 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. Human ear micro-CT 20
  • 22. Human ear micro-CT 21
  • 23. Human ear micro-CT Resolution: 23 m (voxel size) 22
  • 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. 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. Middle ear FE model results1000 Hz 7000 Hz 16000 Hz (x8e3) (x3e4) (x2e5) 25
  • 27. Middle ear FE model results1000 Hz 7000 Hz 16000 Hz (x2e4) (x3e5) (x3e6) 26
  • 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. 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 29
  • 31. SetupNOW FUTURE 30
  • 32. Results rubber sheet363 Hz at 75 dB 1040 Hz at 85 dB 31
  • 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 34
  • 36. OCT results (human)OCT image dataset image correction + segmentation surface generation (triangulation) 35
  • 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-endoscopyTypically used in ENT clinicsC diagnoseD no quantitative data 37
  • 39. Endoscopic moiré• Moiré profilometry 38
  • 40. Endoscopic moiré• Moiré profilometry 39
  • 41. Endoscopic moiré• Endoscopic moiré profilometry > In vivo tool > Quantitative > Simultaneous > with tympanometry: > locate weak spots > Problem: > lens distortions 40
  • 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 resultsIntegrated X-ray shadowimage of 2 Tungsten beadsat 1 Hz with 1 kPa pressure 46
  • 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 48
  • 50. Detection method• Input signal: multisine 49
  • 51. Detection method• Linear output 50
  • 52. Detection method• Non-linear output 51
  • 53. Measurement setup• Measurements on the gerbil middle ear 52
  • 54. Results non-linear distortions 53
  • 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