1. Study of middle ear mechanics at theLab of Biomedical Physics: an overviewJef AernoutsSeptember 13th, 2012

2. BIMEF Laboratory of Biomedical PhysicsUniversity 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 sickness1 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-raytechniques- Non-linear distortions in the middle ear2 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-raytechniques- Non-linear distortions in the middle ear3 5. Motivation Study of middle ear mechanics:Finite Element (FE) modeling 4 6. Motivation Models very sensitive to inputted tympanicmembrane mechanical properties Substantial variability in the literatureMechanical Properties of the Tympanic Membrane:Measurement and Modeling5 7. TM mechanical properties Human TM geometry - Multi-layered - Circular and radial fibersHomogeneous & Isotropic Mechanical properties - Stiffness (Youngs modulus) - Damping or viscoelasticity (Complex modulus) 6 8. Pressure regimes Quasi-static regime Acoustic regime- 0-20 Hz- 20-20000 Hz- Typically- Typically50-1000+ Pa0.02 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 Moir measurement Inverse FE analysis(1) TM, (2): force transducer,(3): piston, (4): LVDT , (5): signalgenerator, (6): feedback control unit FE models10 12. monitorcameravaporizersamplemounterattachedto loadcellpiston thatdrives needle LVDT 13. Results12 14. TM mechanics at acoustic freqs In Bostonfront 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 measurementssound 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 outcome16 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-raytechniques- Non-linear distortions in the middle ear17 19. Middle ear morphology: Why? Human No complete (both bone & soft tissue) datasetsavailable Important for realism of middle ear (FE) models18 20. Ear morphology Histological sections Micro-CTC distinction bone tissue C non-destructiveD destructiveD no soft tissueD tissue deformation C staining > soft tissue19 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-raytechniques- Non-linear distortions in the middle ear23 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 attachment24 26. Middle ear FE model results1000 Hz 7000 Hz16000 Hz (x8e3)(x3e4) (x2e5)25 27. Middle ear FE model results1000 Hz 7000 Hz16000 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-raytechniques- Non-linear distortions in the middle ear27 29. Holography Principle Digitalholography - CCD - Virtual reconstruction: hologram before and after > deformation CCD 28 30. Stroboscopic holography Shutter laser beam/pulsed laser on specificphases Both magnitude and phaseof vibration pattern 29 31. SetupNOW FUTURE 30 32. Results rubber sheet363 Hz at 75 dB1040 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-raytechniques- Non-linear distortions in the middle ear32 34. TM thickness: Why? There is no literature on full-field humantympanic membrane thickness The thickness distribution is an important inputparameter in middle ear (FE) models 33 35. Optical Coherence Tomography Imaging technique Broadband infraredlight source> short coherence> length 34 36. OCT results (human)OCT image datasetimage correction + segmentationsurface 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-raytechniques- Non-linear distortions in the middle ear36 38. Oto-endoscopyTypically used in ENT clinicsC diagnoseD no quantitative data37 39. Endoscopic moir Moir profilometry 38 40. Endoscopic moir Moir profilometry 39 41. Endoscopic moir Endoscopic moir 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 correction41 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 usingX-ray techniques- Non-linear distortions in the middle ear43 45. Idea X-ray imagingC no need for optical access as in the case of LDVC measurements on a closed middle ear cavityD rather low resolution compared to LDV Stereoscopy- Gain 3D information by taking multiple shots at variousangles- Time information from grayscale analysis 3D motion of non-transparent objects44 46. X-ray stereoscopy on rabbit ME Rabbit middle ear Quasi-static pressures - Freqs: 0,550 Hz - Amplitudes: 0,251 kPa Useful for study ofa: 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 pressure46 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-raytechniques- Non-linear distortions in the middle ear47 49. Non-linearity in the ME It is generally believed that the human middleear is a linear system up till 130 dB (SPL) Strong non-linearity in the quasi-static regime Small non-linearity in acoustic regime at highsound pressure levels?- Important for e.g. hearing aids and implantablemicrophones that use high sound pressure levels48 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 ear52 54. Results non-linear distortions 53 55. Thanks...... for your attention!More information and published articles atwww.ua.ac.be/bimefContact:Jef.Aernouts@gmail.com Joris.Dirckx@ua.ac.be 54