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The thickness of the tympanic membrane has to be known for the formulation of mathematical ear models. Using a commercial confocal laser scanning microscope we have found that the tympanic membrane has parts thinner than 10 micron. In this study we were forced to excise the tympanic membranes and due the restricted working distance of the microscope objective, we had to flatten the tympanic membrane onto a glass plate. Although we were able to measure thickness in fresh samples, thickness could still have been altered by the preparation procedure. S. Khanna developed over the years a powerful heterodyne interferometer with confocal pinholes in the illumination and observation arms. Thanks to its sectioning capabilities it can measure vibrations of structures embedded within other tissue without the need to expose the structure. While using this equipment in measuring vibrations in the middle ear, the idea grew that the interferometer could also be used to measure thickness, by tracking the carrier level of the interferometer while the laser focus is driven through the membrane. The method looks full of promises as measurements on animals with the tympanic membrane still in its original niche are possible without a prior preparation of the membrane.

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.

Our hypothesis is that purulent otitis media and otitis media with effusion cause stiffness loss of the tympanic membrane. This loss of stiffness may be persistent and precede the development of retraction pockets and cholesteatoma.Postinflammatory changes such as retraction pockets and cholesteatoma develop in the pars flaccida and in the pars tensa of the tympanic membrane. In our previous experimental studies, stiffness changes were 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. The aim of the current study was thus to investigate whether stiffness changes appear also in the pars flaccida during purulent otitis media.Streptococcus pneumoniae type 3 was injected into the middle ear to induce purulent otitis media. As a measure of pars flaccida stiffness, peak displacement versus middle ear pressure was used. The peak displacement measurements were obtained from full-field moiré; interferometry, which is a noncontacting optical technique for deformation measurements.Ears with purulent otitis media showed increased peak displacement of the pars flaccida at a middle ear pressure of 200 daPa, compared with normal controls.There was a decreased mechanical stiffness of the pars flaccida in acute purulent otitis media. This decreased stiffness may predispose for future retraction pocket formation and cholesteatoma development.

Objective: Tympanic membrane perforations may cause hearing impairment and otorhea. It is a common indication for ear surgery. The aim of the study was to test whether stem cells may enhance the heating of fresh tympanic membrane perforations. Methods: In a first assay, the status of the tympanic membrane at 5 days after myringotomy was tested in five Mongolian gerbils that were treated on one side with embryonic stem cells and on the other side with control substance. In a second assay, nine gerbils were treated in the same way, except that fluorescent-labeled embryonic stem cells were used. The integration of the stem cells into the surface layer of the heating tympanic membrane was assessed with fluorescence microscopy, as well as the differentiation of these cells. Results: In the first assay, all perforations in the treated ears were closed, whereas only two of the untreated ears were closed. The strength of the heated perforation was greater in the stem cell treated tympanic membranes (mean rupture pressure 120 daPa in three treated ears compared to 60 daPa in the one control ear). Two stem cell-treated tympanic membranes remained intact throughout the whole sequence of pressures, whereas only one control tympanic membrane remained intact. In three tympanic membranes in the second assay, a group of fluorescence-doped cells was detected in the region of the perforation. Conclusion: These findings indicate that stem cells enhance the heating of tympanic membrane perforations, possibly by differentiation and integration into the tympanic membrane tissue. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.

Vibration of biological structures is often measured in a reference system that is imposed on the investigator by the accessibility of the object. This imposes a serious handicap on the usability of the results. A method is presented that measures the 3-D components of vibration of the structure and integrates complete 3-D anatomy in the data analysis. A realistic3-D anatomical model of the tested structure is used to determine coordinate transformations and express the motion parameters in intrinsic object reference systems. Results from different experiments can now be unequivocally compared and predictions of mathematical models can accurately be checked. Animations of the vibrating structure can be made to study the motion from all angles, even those not accessible during the experiments. One can also calculate the ratio of vibration amplitudes at different landmark points, check whether the structure has a fixed rotation axis, or calculate the vibration along an observation axis that was used in experiments with a completely different experimental approach. We present as an example a study on the vibration of the malleus. The application of our procedure is not limited to problems in the biomedical research area, but it is of general use in [bio-] engineering applications.

We study a statistical ensemble of multimode laser beams. Each beam is made up of an incoherent superposition of off-axis polychromatic Hermite–Gaussian modes. We obtain analytic expressions for the squared beam radius, the waist position, the Rayleigh range, the skewness parameter, the kurtosis parameter, and the squared beam-propagation factor. We demonstrate that the squared beam radius has a quadratic dependence on the distance from the waist plane. The skewness parameter may be different from zero in the near-field zone, but it tends to zero in the far-field zone. The kurtosis parameter in the far-field zone coincides with the kurtosis parameter of the incoherent superposition of on-axis modes.

It has been shown that in cardiovascular risk management, stiffness of large arteries has a very good predictive value for cardiovascular disease and mortality. This parameter is best known when estimated from the pulse wave velocity (PWV) measured between the common carotid artery (CCA) in the neck and femoral artery in the groin, but may also be determined locally from short-distance measurements on a short vessel segment. In this work, we propose a novel, non-invasive, non-contact laser Doppler vibrometry (LDV) technique for evaluating PWV locally in an elastic vessel. First, the method was evaluated in a phantom setup using LDV and a reference method. Values correlated significantly between methods (R

Eardrum deformation induced by quasi-static middle ear pressure was studied at progressive stages of dissection of gerbil temporal bones. With our high resolution moire 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.

An opto-electronic projection moire apparatus was developed for in-vitro studies of the eardrum. Moire topograms are generated by real-time video image subtraction, yielding 25 new interferograms per second. By using different reference images, both shape and deformation fringes can be obtained, without manipulating the object or the setup. Calibration measurements show a measuring precision of 5 micrometers . The setup is used to measure the shape and deformation of the eardrum. Parameters such as, for instance, the volume displacement of the pars flaccida, can be calculated from computer evaluations of the topograms.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

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.

Holography and moire topography are very valuable tools for the study of the shape, the deformation, and the vibration of delicate biological structures such as the eardrum. Best results are obtained if the object surface has high diffuse reflectivity, without specular reflections. May biological objects do not have these qualities by nature, so that application of reflective coatings can strongly improve measuring results. In the present paper the optical and mechanical properties of reflective coatings based on bronze powder, white Chinese ink, and magnesium oxide are discussed. Measurements of reflected intensity distribution show that white Chinese ink and MgO have superior optical qualities: they can strongly enhance diffuse reflectivity, while completely suppressing all specular reflections. Electron microscopy shows that these coatings have a layer thickness of 7.5 micrometer and 17 micrometer, respectively. Phase shift moire topography is used to measure the displacement of a thin plastic membrane which is deformed by small static pressures. It is shown that the coatings do not cause deformation artifacts within the measuring resolution of 2.5 micrometers. Application results of in-vitro shape and deformation measurements on coated tympanic membranes are given.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical imaging systems often suffer from distortion artifacts which impose important limitations on the direct interpretation of the images. It is possible to correct for these aberrations through image processing, but due to their calculation-intensive nature, the required corrections are typically performed offline. However, with image-based applications that operate interactively, real-time correction of geometric distortion artifacts can be vital. We propose a new method to generate undistorted images by implementing the required distortion correction algorithm on a commercial graphics processing unit (GPU), distributing the necessary calculations to many stream processors that operate in parallel. The proposed technique is not limited to affine lens distortions but allows for the correction of arbitrary geometric image distortion artifacts through individual pixel resampling at display rates of more than 30 frames per second for fully processed images (1024×768 pixels). Our method enables real-time GPU-based geometric lens distortion correction without the need for additional digital image processing hardware.

We propose a new technique to measure the 3D motion of marker points along a straight path within an object using x-ray stereo projections. From recordings of two x-ray projections at different angles, the 3D coordinates of marker points can be determined. By synchronizing the x-ray exposure time to the motion event, a moving marker leaves a trace in the image of which the gray scale is linearly proportional to the marker velocity. By measuring the marker gray scale along the motion path, the velocity at each point is determined and the position as a function of time is obtained by integration. In combination with the 3D information from two stereo recordings, the full 3D motion is obtained. The difference in position between the new method and laser vibrometry was less than 5 µm. The 3D motion measurement is performed within seconds, making the method ideal for applications in biomechanics. In combination with a full CT-scan of the object, the motion information on the marker points can be used to measure and visualize how an internal rigid 3D structure moves. We demonstrate the method on the malleus ossicle motion in the gerbil middle ear as a function of pressure on the eardrum.

A method for high-resolution measurement of 3D coordinates and translations of small objects is presented, using single x-ray point-source stereoscopy. The theory of the pinhole method is re-derived for a point-source x-ray projection setup using a conical beam. The method is then implemented using a micro x-ray tomography setup with a single 8 µm point source. Stereo projections are obtained by rotating the object over 90° between subsequent recordings, and microscopic tungsten beads are used as marker points. The accuracy of the method is tested on a spherical calibration object, and found to be better than 10 µm. Using a translation stage, the measurement uncertainty for translation measurements was found to be better than 5 µm along both axes parallel to the detector and at right angles to the detector. Due to the short measurement time and the high resolution, the method will be useful to study the biomechanics of small specimens, and the principle of the method is useful in any cone-beam-based setup.

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.

To measure the surface shape and shape change of soft biological material, the use of a non contactingmetrological technique is imperative. One of these techniques is moire contouring, which is particularlyinteresting because of its simplicity and low cost. We propose a method to mathematically reconstruct asurface shape from moire topograms. The method is based on the recording of three topograms which are shifted in phase by translating the object. The method is implemented in an apparatus which fully automatically performs all required steps to finally yield a 512 by 512 point matrix of surface height values,with a height measuring resolution of 20 pm. The resolution for measuring small height displacements is 2pm. Due to this high resolution, it is possible to investigate the deformation of the tympanic membrane,caused by small pressure changes in the middle ear cavity. Full field deformation data are shown. The datacan be used to obtain information on the movement of the manubrium, or to calculate volume displacementsand surface area changes.1. INTRODUCTIONTo measure the surface shape of delicate biological specimens such as the tympanic membrane (TM),it is imperative to use a non contacting metrological technique. Moire topography is a simple and low cost

The shape of the tympanic membrane is fairly complicated 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. Precise measurements of the tympanic membrane shape are not available in literature. To measure the shape of a very thin, curved biological membrane a technique is required which does not deform the surface during the measurement. Casting techniques are therefore not well suited. A noncontacting measurement technique based on moire interferometry proved to be a better tool. A moire shift interferometer was used to measure with great precision the shape of the external surface of human and cat tympanic membrane. The dense matrix of z(x,y) values thus obtained does not only describe the shape with high spatial resolution but may also be used to calculate different geometrical parameters. As an example of direct application the authors have calculated the area of the curved surface to the pars tensa and pars flaccida for a human and a cat tympanic membrane.

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 moire 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.

Recently, a method using multisine excitation was proposed for estimating the frequency response, the nonlinear distortions and the disturbing noise of weakly nonlinear time-invariant systems. This method has been demonstrated on the measurement of nonlinear distortions in the vibration of acoustically driven systems such as a latex membrane, which is a good example of a time-invariant system [1]. However, not all systems are perfectly time invariant, e.g. biomechanical systems. This time variation can be misinterpreted as an elevated noise floor, and the classical noise estimation method gives a wrong result. Two improved methods to retrieve the correct noise information from the measurements are presented. Both of them make use of multisine excitations. First, it is demonstrated that the improved methods give the same result as the classical noise estimation method when applied to a time-invariant system (high-quality microphone membrane). Next, it is demonstrated that the new methods clearly give an improved estimate of the noise level on time-varying systems. As an application example results for the vibration response of an eardrum are shown.

A method for full field 3-D surface reconstruction is proposed. The method is based on shadow moire topography and makes use of four contourograms shifted in phase by translating the object. The implementation of the method in a fully automated apparatus is described. Some application examples are given. 1.

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 method is proposed to calculate the area change and the volume displacement of a deformed membrane from the measurement of its displacement amplitude on a regular grid of observation points. The method is demonstrated on a circular latex membrane deformed by air pressure. The displacement data are obtained by phase shift moire interferometry. Area changes down to 0.5% and volume changes down to 16.1 mm(3) are measured, and error flags are determined.

A new calibration procedure for phase shift moire interferometry is proposed. The method does not ask for a high precision machined calibration object and makes use only of the moire setup itself. The procedure is fast and fully automatic. The fringe plane distance lambda was determined with a precision of 1.3%. We present control measurements on a plane surface and a perfect sphere confirming the value and the precision of lambda.

A new method fur full field automatic 3-D surface reconstruction is proposed which makes use of multiple contourograms shifted in phase by object translation. The method is demonstrated for shadow moire topography. It is shown that surface reconstruction can be done fast and with a resolution at least 10 times higher than the fringe distance of the measuring setup. Convexity and concavity of the surface are automatically determined. Also shown is the possibility of measuring irregular surfaces with very sudden height jumps.