Optimized robotic setup for automated active thermography using advanced path planning and visibility study.

In-line inspection of advanced components remains a challenging task in industry. The authors will describe an automated methodology that uses numerical simulations to automatically determine the best set of experimental parameters to inspect the structure on defects using active thermography. The inspection is performed using a robotic arm and advanced path-planning tools to determine the optimal positions of the measurement points and excitation points. During the path planning, the directional emissivity is considered for the complex surface, and a minimization of the amount of measurement points is performed. The numerical simulation optimization used a genetic algorithm and spline regression model to optimize the heat power, robot speed, camera frame rate, and excitation timing to fulfill the automatic inspection.

The mechanical reaction of the pars flaccida of the eardrum to rapid air pressure oscillations modeling different levels of atmospheric disturbances.

Atmospheric pressure fluctuations (APF) might induce mechanical effects in the pars flaccida (PF) of the eardrum. To clarify these effects, different kinds of pressure oscillations (PO), chosen within the range of naturally occurring APF, were applied to the middle ears (ME) of gerbils. The linear displacement of the PF during a PO in the ME was measured by laser interferometry. The compliance of the PF to PO was calculated as the ratio of the amplitude of a PF oscillation to the amplitude of a PO. The displacement of the PF traced the PO in the entire range of frequencies (from 10mHz to 200mHz) and amplitudes (from 10Pa to 110Pa) applied to the ME. Moreover, the PF is found to be displaced by pressure pulses of a few pascals only using a PO with a complex shape. The differences found in the compliance of the PF due to PO with low (less than 20Pa) and high (more than 90Pa) amplitude point out that the mechanism of pressure regulation in the ME through the mechanical reaction of the PF in gerbil ears is better adapted to ordinary levels of natural APF than to extraordinary levels. The implications of these findings for the physiology of the human ME with respect to adaptation to natural APF are discussed.

Thickness distribution of fresh eardrums of cat obtained with confocal microscopy.

The aim of this study was to measure the spatial thickness distribution of the cat tympanic membrane (TM), a very thin, virtually transparent and delicate biological membrane. Axial fluorescence images taken perpendicular through isolated TM were recorded for five different cats using confocal laser scanning microscopy. Thickness was measured on the cross-section of the membranes in the axial images. A correction for focal shift due to refractive-index mismatch was applied. Similar thickness distributions were obtained in all measured samples (n = 9). The pars tensa had a rather constant thickness in the central region between the annulus and manubrium. The thickness increased steeply toward the peripheral rim. Thickness was smallest in the inferior region, with values ranging between 5.5 and 9 microm in the central part and up to 50 microm near the annulus. More superiorly, thickness was slightly higher, up to 20 microm, between the annulus and manubrium. The anterior part was thicker than the posterior side. These findings are strongly different from a current value in the literature. Our data allow a more precise representation of the eardrum in mathematical models, which are a prerequisite for a better understanding of middle-ear mechanics. The optical sectioning technique of the confocal microscope did not result in any preparation artifacts and was therefore also used to quantify shrinkage due to preparation of histological sections of TMs.

Three-dimensional modelling of the middle-ear ossicular chain using a commercial high-resolution X-ray CT scanner.

The quantitative measurement of the three-dimensional (3-D) anatomy of the ear is of great importance in the making of teaching models and the design of mathematical models of parts of the ear, and also for the interpretation and presentation of experimental results. This article describes how we used virtual sections from a commercial high-resolution X-ray computed tomography (CT) scanner to make realistic 3-D anatomical models for various applications in our middle-ear research. The important problem of registration of the 3-D model within the experimental reference frame is discussed. The commercial X-ray CT apparatus is also compared with X-ray CT using synchrotron radiation, with magnetic resonance microscopy, with fluorescence optical sectioning, and with physical (histological) serial sections.

Design, construction and mechanical optimisation process of electrode with radial current flow in the scala tympani.

A 48 contact cochlear implant electrode has been constructed for electrical stimulation of the auditory nerve. The stimulating contacts of this electrode are organised in two layers: 31 contacts on the upper surface directed towards the habenula perforata and 17 contacts connected together as one longitudinal contact on the underside. The design of the electrode carrier aims to make radial current flow possible in the cochlea. The mechanical structure of the newly designed electrode was optimised to obtain maximal insertion depth. Electrode insertion tests were performed in a transparent acrylic model of the human cochlea.

Effect of middle ear components on eardrum quasi-static deformation.

Eardrum deformation induced by quasi-static middle ear pressure was studied at progressive stages of dissection of gerbil temporal bones. With our high resolution moiré interferometer we recorded the shape and deformation of the eardrum along a line perpendicular to the manubrium and through the umbo, at different middle ear pressures. The deformation was measured from the medial side, after serially removing the cochlea, removing the stapes, cutting the tensor tympani, exposing the incudo-mallear joint, and cutting the anterior bony process which connects the malleus to the tympanic bone. The mean displacement as a function of pressure was also determined at all stages of dissection. Removing the cochlea and stapes, and cutting tensor tympani has no effect on static eardrum deformation. Exposing the incudo-mallear joint increases eardrum movement, and cutting the anterior bony connection between malleus and temporal bone strongly changes eardrum rest position and further increases its displacement.

Area change and volume displacement of the human tympanic membrane under static pressure.

Direct measurements are presented of the area change and volume displacement of a human tympanic membrane under static pressures in the range of -1.6 KPa to +1.6 kPa. The area change is given separately for the pars tensa and the pars flaccida. For the pars tensa a strong asymmetry in area change under positive and negative pressure is observed. The volume displacement is also given separately for the pars tensa and the pars flaccida. The volume displacement of the entire TM agrees very well with volume displacement data in literature on tympanometry. It is shown further that a linear relationship between umbo displacement and volume displacement exists. The compliance of the tympanic membrane under static pressure load is compared to acoustic compliance measurements at low frequencies, and found to be a factor 2.5 higher than the compliance at 500 Hz.

Human tympanic membrane deformation under static pressure.

The effect of static pressures in the range of plus and minus 1.6 kPa on the shape of tympanic membrane is measured using a non-contacting optical technique on a fresh human temporal bone. Full field data of the deformation are presented as well as cross-sections along two major directions. Strong asymmetry between medial and lateral movements is demonstrated. The displacement of the umbo is compared to other work. The rotation angle of the manubrium in function of pressure is calculated and also compared to other work. It is demonstrated that the rotation angels can not account for the measured movement of the umbo, which leads to the conclusion that for static high pressure levels the classical hypothesis of rotation around a fixed axis has to be abandoned. The comparison with data of TM displacement under dynamic stimuli is discussed.

Measurement and modeling of boundary shape and surface deformation of the Mongolian gerbil pars flaccida.

The shape of the pars flaccida (PF) boundary and its pressure induced deformation was measured in five Mongolian gerbil ears, using an opto-electronic moiré interferometer. To determine the PF boundary, membranes were deformed by middle ear (ME) pressures of -2 kPa and +2 kPa. The boundary of the PF was defined as the locus of points where the pressure induced deformation begins. To a very high precision, this boundary was found to be a circle with the same radius for both over- and underpressure deformations. Between animals the radius varied from 0.760 mm to 0.778 mm. We show that the shape of the PF, while being deformed by static pressure in the ME, can be modeled as part of a sphere. Volume displacement can then be calculated as the volume enclosed by the sphere cap, delimited by the circular PF boundary plane. Volume displacement was calculated for membranes deformed by 400 Pa ME overpressure and -400 Pa ME underpressure. The agreement of the experimental data with the sphere cap model is shown to be very good, and results in a volume displacement measuring accuracy which is better than 10%.

Shape and derived geometrical parameters of the adult, human tympanic membrane measured with a phase-shift moiré interferometer.

The shape of the tympanic membrane is fairly complex and seems to be of significant importance in the coupling of the acoustic sound pressure in the external ear canal to the motion of the middle ear ossicles. A moiré shift interferometer was used to measure with great precision the shape of the external surface of human tympanic membrane. The dense matrix of z(x,y) values thus obtained is used to calculate different geometrical parameters (area, curvature, ...). We show further how the same data can be used to specify exactly the shape of the tympanic membrane in a mathematical finite-element model of the middle ear.

Volume displacement of the gerbil eardrum pars flaccida as a function of middle ear pressure.

The pars flaccida (PF) is a small region of the eardrum, with elasticity and histology completely different from the rest of the membrane, which has often been attributed a pressure regulating function for the middle ear (ME). In this paper, the volume displacement of the PF as a function of ME pressure is discussed. The deformation of the PF was measured in vitro in five Mongolian gerbil ears, by means of an opto-electronic moiré interferometer. Volume displacement was determined at small intervals in three sequential pressure cycles, in the range of +/- 0.4 kPa, +/- 2 kPa, and again +/- 0.4 kPa. The displacement was found to be a highly non-linear function of pressure, with a strong increase up to 0.4 kPa ME over- or underpressure and remaining nearly unchanged for pressures beyond 0.4 kPa. In all animals, maximal volume displacement was less than 0.5 microl, or 0.2% of total ME air volume. Clear hysteresis was found between the deformations at the same pressure level in the increasing and decreasing parts of the pressure cycles. Membrane behavior in the first 0.4 kPa pressure cycle was significantly different from that in the second 0.4 kPa cycle, which followed the 2 kPa pressure cycle. The results indicate that the ME pressure change regulation function of the PF is limited to very small pressure changes of a few hundred Pa around ambient pressure, and that larger ME pressures cause at least short-term changes in the membrane's behavior.

Displacement of the gerbil tympanic membrane under static pressure variations measured with a real-time differential moire interferometer.

It is thought that chronic middle ear disease ultimately causes changes in the stiffness and elasticity of the tympanic membrane, but it is unknown whether such changes occur early in the course of the disease. In order to analyze mechanical changes in different parts of the tympanic membrane, a full field moire interferometry technique was utilized to measure the shape and real-time displacement in response to positive and negative pressure gradients applied across the tympanic membrane. The measurements were performed on fresh isolated temporal bones from the Mongolian gerbil. In order to gain sufficient visual access to the pars tensa for the moire measurements, the tympanic bulla was opened, the tensor tympani muscle and the incudo-stapedial joint were cut, and part of the medial wall of the tympanic cavity was removed. The malleus and incus and their ligaments were kept intact. The specimens were kept continuously humidified with an evaporator or in a humid chamber, since otherwise the tympanic membrane dries out in a few minutes when its medial surface is exposed. This desiccation reduces the elasticity and cause shrinkage which results in a reduction of the height of the cone constituted by the pars tensa. Profiles of the tympanic membrane at rest and under different pressure conditions were extracted from the moire interferograms. The tympanic membrane and ossicular complex exhibit a hysteresis effect as differences in the displacement patterns under identical pressure gradients during the loading and the unloading phase; a residual displacement of the pars tensa was for instance seen after the pressure gradient across the tympanic membrane was eliminated.

Tympanic membrane displacement patterns in experimental cholesteatoma.

Tympanic membrane (TM) stiffness changes in the pars tensa in response to experimentally induced ear canal cholesteatoma by obstruction of the ear canal were studied. To this aim TM displacement versus pressure was measured with a high resolution, differential moiré interferometer. The measurements were performed on fresh, isolated gerbil temporal bones after removal of the cholesteatoma bulk. Besides an overall stiffness reduction we found that local stiffness variations were present in nine out of 18 studied ears. The stiffness changes as a function of time after ear canal obstruction had a pattern similar to those previously shown to develop in response to various forms of otitis media, showing that the TM stiffness properties decrease in a similar way in response to different inflammatory middle ear diseases. The stiffness changes correlated with an increased overall TM thickness and increased thickness of the lamina propria in particular as measured in histology sections. The stiffness changes may play an important role in the pathophysiology of cholesteatoma.

Shape and displacement patterns of the gerbil tympanic membrane in experimental otitis media with effusion.

This study assesses the visco-elastic properties of the tympanic membrane (TM) in isolated gerbilline temporal bones as a function of time after inducing experimental otitis media with effusion (OME). To do this we measured the TM displacements produced by application of sequences of static pressures across the TM, with a high resolution, real-time, differential moiré interferometer, and the results were compared with measurements on healthy ears. Two methods of producing OME were used: in one group tubal plugging was performed to produce mild OME (the 'TP group'); in the other group electro-cauterization of the nasopharyngeal orifice of the Eustachian tube was used to cause a severe form of OME (the 'EC group'). The measurements were performed from one day up to ten weeks after surgery. In the TP group the displacement fringe patterns were normal, i.e. qualitatively they resembled the patterns of the control group. Quantitatively there was a significant decrease of displacement for a given pressure on the first day after surgery, followed by a trend of increase with time; after seven to ten days the displacement was larger than in the control group. In the EC group the displacement was significantly reduced after half a week, followed by a trend of increase with time, similar to what was found in the TP group; at one week the displacement was larger than in the control group, and at ten weeks the largest displacement was recorded. In the EC group the displacement patterns were often irregular; in some cases with changes suggesting the presence of weak spots in the TM where retraction pockets most likely could develop. OME seems to affect the stiffness of the TM promptly so that it is a potential parameter for early diagnosis. The stiffness changes may, if measurable in the clinical situation, become prognostic parameters in the treatment of OME.

Displacement pattern of the normal pars flaccida in the gerbil.

OBJECTIVE: The aim of the current study was to assess the mechanical stiffness properties of the normal pars flaccida and to compare the results with those obtained in earlier studies on the pars tensa. BACKGROUND: Postinflammatory changes such as retraction pockets and cholesteatoma develop in the pars flaccida as well as in the pars tensa of the tympanic membrane. In these authors' previous experimental studies, stiffness changes are shown to develop early in the pars tensa in response to purulent otitis media and otitis media with effusion. These changes are suggested to be precursors to a later development of retraction pockets and cholesteatoma. In the clinical situation, retraction pockets are often found in the pars flaccida only. This study will establish the stiffness properties of the normal pars flaccida and form a base for forthcoming studies of the pars flaccida in response to otitis media with effusion and purulent otitis media, as well as retraction pocket formation and cholesteatoma. METHODS: A measure for the mechanical stiffness properties of the normal pars flaccida in the gerbil was assessed as its displacement for a given transtympanic pressure. The method used was moiré interferometry, which is a noncontacting optical technique to measure the shape of the surface of an object. RESULTS: The displacement of the pars flaccida was a nonlinear and asymmetric function of pressure. The displacement per pressure unit rose steeply at low middle ear pressures to level out and reach a steady state at higher pressures. The displacement versus pressure characteristics for the pars flaccida strongly differed from those of the pars tensa. The pars tensa seemed more elastic. CONCLUSION: Reference values for displacement versus pressure characteristics of the normal gerbil pars flaccida were obtained using a moiré interferometry method. The mechanical stiffness properties of the normal pars flaccida were strongly different from those of the pars tensa.

Numerical assessment of TOAE screening results: currently used criteria and their effect on TOAE prevalence figures.

The literature on neonatal hearing screening by means of oto-acoustic emissions (OAE's) presents various prevalence figures, and gives little quantitative information on the procedure used to score the recordings. If the OAE test is to be interpreted by users who do not have the opportunity to develop intuitive interpretation skills through extensive training, a clear numerical decision criterion is needed. The present paper discusses the scoring procedure used by 25 teams, which together screen 22,356 neonates annually. More than 60% of the groups involved in this study use visual interpretation of the recorded OAE response, together with numerical criteria. Amongst the teams, 21 different ways of numerical scoring are used. It is shown that for a given set of OAE recordings, prevalence varies from 61% to 90%, depending on the numerical decision criterion being applied. We conclude that at this moment no consensus exists regarding the numerical criterion to be used when assessing OAE screening results. In view of the strong effect of criteria on the outcome of OAE screening, such consensus is urgently needed, but should be based on sensitivity and specificity figures for each scoring technique.

A simple method for checking the illumination profile in a laser scanning microscope and the dependence of resolution on this profile.

One of the conditions for a laser scanning microscope to reach its optimal performance is for it to operate at its full numerical aperture (NA). In most commonly used systems, the illumination intensity at the back focal plane of the objective lens is apodized. This paper presents a simple method using a photodiode for checking the actual illumination intensity profile. We show as an example the measured profiles of a laser beam when working with two high-NA immersion objectives in two different confocal systems, and also show that in theoretical studies of the point-spread function, the assumption of a flat compared with a truncated Gaussian beam profile gives rise to severe discrepancies. The measured profiles also serve as an indication of the necessity of a realignment of the optical system.

Overview of safety imaging methods for newly designed cochlear implant electrodes.

Different individual test methods and protocols have been reported for the in-vitro evaluation of temporal bones implanted with newly designed cochlear implant electrodes, prior to human implantation. In practice, however, these methods may not always give the required information. In this study, a large battery of tests has been evaluated using the electrode as a fixed parameter. Standard clinical x-ray gave the best information to evaluate the electrode's position. Light microscopic evaluation and polishing technique studies proved to be the most valuable techniques to evaluate endocochlear damage.

Comparison of the accuracy of digital stereophotogrammetry and projection moiré profilometry for three-dimensional imaging of the face.

The aim of this study was to compare the three-dimensional (3D) imaging accuracy between a digital stereophotogrammetry device and a projection moiré profilometry setup using anatomical models in conjunction with surface matching software. Twenty-two 3D surface models of the middle third of the face derived from computed tomography (CT) scans were used to fabricate photopolymer models by rapid prototyping. These were digitized using digital stereophotogrammetry and projection moiré profilometry. The 3D surface models acquired were compared for shape differences with the original CT models using surface matching software. Global registration between each pair of corresponding models was carried out using an iterative closest point algorithm. The mean surface deviations following registration were used to calculate Bland-Altman limits of agreement between the two methods. The distributions of measured surface differences were used to calculate L-moments. Paired t-tests were carried out for hypothesis testing. Correlation between difference and mean was -0.3, and 95% limits of agreement were -0.084mm and 0.064mm. No statistically significant differences in mean measurement error (L1 moments) were observed (P=0.1882). The experimental moiré profilometry setup employed produced 3D models of facial anatomy of comparable accuracy to a widely used commercialized digital stereophotogrammetry device.

Nonlinearity in eardrum vibration as a function of frequency and sound pressure.

It is generally accepted that the middle ear acts mainly as a linear system for sound pressures up to 130 dB SPL in the auditory frequency range. However, at quasi-static pressure loads a strong nonlinear response has been demonstrated. Consequently, small nonlinear distortions may also be present in the middle ear response in the auditory frequency range. A new measurement method was developed to quickly determine vibration response, nonlinear distortions and noise level of acoustically driven biomechanical systems. Specially designed multisines are used for the excitation of the test system. The method is applied on a gerbil eardrum for sound pressures ranging from 90 to 120 dB SPL and for frequencies ranging from 125 Hz to 16 kHz. The experiments show that nonlinear distortions rise above noise level at a sound pressure of 96 dB SPL, and they grow as sound pressure increases. Post-mortem changes in the middle ear influence the nonlinear distortions rapidly until a stabilization occurs after approximately 3h.