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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 with 90o separation angle, 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. From the gray scale along the motion path, the 3D motion (velocity) is obtained. The path of motion was reconstructed and compared with the applied waveform. The results showed that the accuracy is in order of 5%. The difference of displacement amplitude between the new method and laser vibrometry was less than 5μm. We demonstrated the method on the malleus ossicle motion in the gerbil middle ear as a function of pressure applied on the eardrum. The new method has the advantage over existing methods such as laser vibrometry that the structures under study do not need to be visually exposed. Due to the short measurement time and the high resolution, the method can be useful in the field of biomechanics for a variety of applications.

When a fluid flowing through an elastic vessel is subjected to a sudden change in pressure gradient, pressure pulses will propagate through the fluid. Velocity of these pulse waves (PWV) can be determined by simultaneous detection of wall distension on two separate points on the vessel wall, along its trajectory. PWV depends on wall stiffness, and under certain circumstances, wall stiffness can be calculated from the propagation velocity. Optical interferometry is a noncontacting technique that allows measurement of wall distension on discrete locations. In this work we propose a miniaturized dual-beam laser Doppler vibrometer (LDV) to measure wall distension simultaneously at two locations. Our dual-beam LDV is based on a single laser source and one acousto-optic modulator with as much as possible of the interferometer optics shared among the different beams. The dual-beam LDV was used for simultaneous detection of wall distension of several elastic vessels of different stiffness. We found that PWV as measured in elastic vessels agrees well with theoretically expected values, and measurement precision is better than 5%. Moreover, the dual-beam LDV performs almost as good as commercial systems for detection of PWV. The dual-beam LDV can have applications in cardiovascular risk management. Stiffness of large arteries has a very good predictive value for cardiovascular disease and overall mortality. This parameter can be estimated from arterial PWV. Current methods to measure arterial PWV suffer from several shortcomings. A dual-beam LDV can offer substantial advantages over existing techniques.

Optical lens systems generally contain non-linear distortion artifacts that impose important limitations on the direct interpretation of the images. Image processing can be used to correct for these artifacts, but due to the calculation-intensive nature of the required distortion correction process, this is usually performed offline. This is not an option in image-based applications that operate interactively, however, where the real-time display of distortion corrected images can be vital. To this end, we propose a new technique to correct for arbitrary geometric lens distortion that uses the parallel processing power of a commercial graphics processing unit (GPU). By offloading the distortion correction process to the GPU, we can relieve the central processing unit (CPU) of doing this computationally very demanding task. We successfully implemented the full distortion correction algorithm on the GPU, thereby achieving a display rate of over 30 frames/sec for fully processed images of size 1024 x 768 pixels without the need for any additional digital image processing hardware.

We have developed a simple digital speckle pattern interferometry (DSPI) and shearography setup to measure the displacement and the corresponding strains of small complex bony structures. We choose both optical techniques because we want to obtain very small deformations (± 20 μm) of small objects (± 1cm). Furthermore full field and in situ measurements are preferred. We first use a Michelson DSPI arrangement with phase shifting. In this way we can obtain the out-of-plane displacements precisely. Second, shearography is introduced to measure the derivative of the out-ofplane displacement. In this way some intrinsic disadvantages of DSPI can be overcome. We have developed these setups to measure the out-of-plane deformations of (small) bird beaks when realistic external forces are applied. In this way, we have a full field validation measurement to which we can compare the outcome of realistic finite element models. The aim is to determine whether the shape, and not only the size, of the bird beaks are optimized to deal with the biting forces that a species encounters. This quantitative analysis will help biologists to investigate if beak morphology is adapted to feeding habits. Applying the method to the famous evolution model of the Darwin's finches will provide scientific proof of functional evolution. In this paper we will present both the DSPI and shearography setup, a comparison of the performance of both techniques on a simple deflection of a cantilever beam and the first results obtained on loaded bird beaks.

Structured light projection techniques are an important and popular approach for whole-field surface topography. Within this branch, projection moire interferometry is our preferred optical metrology method. The use of liquid crystal display (LCD) projectors to produce structured light patterns has been proposed and used before in projection moire. It allows fast and easy adaptation of the grid pitch and thus measurement sensitivity. In this paper we will show how using a second liquid crystal panel makes the projection moire technique even more versatile and performant: The setup incorporates optical demodulation (OD) which in turn allows for accurate phase-shifting and the use of phase-shifting algorithms (PSAs). The Z-resolution is high and no filtering or interpolation is needed in X-Y by using the gray scale value variations through the phase-shifting and optical demodulation. Thus, we make optimal use of the camera pixel resolution and achieve an uncompromised measuring resolution. Furthermore, the setup is entirely digitally controlled, needs no physical interaction and avoids mechanically moving component. The low-cost setup, technique and theory will be covered in this talk. The resolution and other performance properties will be discussed and demonstrated. And to conclude, an application to achieve elasticity parameters of membranes will be shown. interferometry is our preferred optical metrology method. The use of liquid crystal display (LCD) projectors to produce structured light patterns has been proposed and used before in projection moire. It allows fast and easy adaptation of the grid pitch and thus measurement sensitivity. In this paper we will show how using a second liquid crystal panel makes the projection moire technique even more versatile and performant: The setup incorporates optical demodulation (OD) which in turn allows for accurate phase-shifting and the use of phase-shifting algorithms (PSAs). The Z-resolution is high and no filtering or interpolation is needed in X-Y by using the gray scale value variations through the phase-shifting and optical demodulation. Thus, we make optimal use of the camera pixel resolution and achieve an uncompromised measuring resolution. Furthermore, the setup is entirely digitally controlled, needs no physical interaction and avoids mechanically moving component. The low-cost setup, technique and theory will be covered in this talk. The resolution and other performance properties will be discussed and demonstrated. And to conclude, an application to achieve elasticity parameters of membranes will be shown.

The middle ear ossicles transmit sound from eardrum to inner ear under largely varying ambient pressure conditions. To protect the structures within the cochlea from excessive footplate incursions the configuration of the ossicles changes with pressure. Sequences of micro CT-scans were acquired from gerbil temporal bones under static ear canal pressures ranging from -450 to +450 daPa. These image stacks were used to track the 3D motion and deformations of the ossicles as a function of pressure using hyperelastic warping [1]. Using the scans for zero pressure, accurate finite-element reference models were generated for each of the ossicles. With the difference between these template images and the target image data recorded in a deformed configuration as a driving force, the warping algorithm displaced and deformed the finite-element models of the ossicles in order to align the deformed template with the target data. Position changes of the ossicles within the middle ear cavity and deformation of the ossicles and the tympanic membrane were all measured in a same preparation. For each static pressure load a finite-element ossicular chain model is obtained in the run and can be used for further analysis under acoustic stimulation.

Recently, a measurement set-up was presented to detect small nonlinear distortions in the vibration of acoustically driven mechanical systems. A speaker generates a specially designed multisine excitation signal that drives the vibration of a test object. The generated sound pressure is measured with a probe microphone in front of the test object, and an heterodyne vibrometer measures the corresponding vibration. Due to the high degree of linearity of the heterodyne technique, very small nonlinear distortions can be detected. In this paper the set-up is used to verify whether small nonlinear distortions are present in the vibration of the middle ear system, which is classically considered to be a completely linear system. In vitro measurements on the right ear of an adult male gerbil proved that nonlinear distortions are present in the vibration of the tympanic membrane. Similar results were seen in measurements on the left ear. The influence of post-mortem changes on the nonlinear behaviour of the middle ear was verified in a number of successive measurements. These indicated that the nonlinear behaviour of the middle ear decreases in time.

In unstable objects, such as biological specimens, vibrational patterns can change quickly with time. To determine phase relationships between several vibrating points in such an object, it is therefore necessary to measure those points simultaneously. We describe a dual channel heterodyne interferometer capable to acquire vibrational data at two arbitrary spatial points simultaneouly over the entire acoustic frequency range. The design allows extension to four or even eight independent channels. Channel cross-talk is measured to be about -30 dB, below the S/N ratio within the signal channel. Velocity resolution is estimated to be 10 mu m/s, corresponding to an amplitude resolution of 1.5 nm at 1 kHz.

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.

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.

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.

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.

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.

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.