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PubMed1992

A visual nonlinearity fed by single cones.

An intensive nonlinearity in the visual system can produce distortion products, or difference frequency gratings, when observers view two high contrast, high spatial frequency interference fringes of slightly different frequency or orientation added together at the retina. These distortion products are visible even when the two fringes imaged on the retina are above the resolution limit. Our experiments take advantage of this nonlinearity to measure the spatial filtering in the visual system following the formation of the retinal image, but preceding the site of the nonlinearity. The point spread function corresponding to this spatial filter is so small that it can be entirely explained by light integration within the apertures of foveal and parafoveal cones. The small size of this point spread function implies that (1) laser interferometry avoids contrast losses inherent in the eye's optics at spatial frequencies as high as 130 c/deg, (2) retinal scatter causes negligible image degradation in the fovea and parafoveal retina, (3) eye movements have little or no effect on contrast sensitivity to the distortion product and (4) that there is no neural spatial summation in the visual system prior to the site of the nonlinearity. Distortion products could also be observed when a bright interference fringe was briefly flashed on the fovea and a test interference fringe was viewed through the resulting afterimage. Measurements of the point spread function at stages in the visual system that precede the generation of this distortion product were similar to those obtained with simultaneous presentation of the two fringes, implying that the aftereffect of light adaptation is extremely local, no larger than the dimensions of single cones.

Adaptation, Ocular↗
PubMed1993

Aging and neural spatial contrast sensitivity: photopic vision.

This study investigated the extent to which older adults' loss in spatial contrast sensitivity at a photopic level is attributable to neural changes in the aged visual system. Laser interferometry was used to generate interference fringes which bypass the optics of the eye in presenting a grating target on the retina. Older adults in good eye health exhibited on average a small but statistically significant loss (0.1-0.2 log unit) in contrast sensitivity across the spatial frequency range tested, although there was considerable overlap between young and old adults. This loss in contrast sensitivity for interference fringes accounted for less than half of the photopic contrast sensitivity loss at higher frequencies reported for older adults in studies using conventional direct-viewing techniques in which the optics of the aged eye are not bypassed. We conclude that neural changes in the aged visual system have a rather minor contribution to older adults' loss in spatial contrast sensitivity at a photopic level.

Adolescent↗
PubMed1993

Serial spatial filters in vision.

Observers viewing two superimposed laser interference fringes of nearly equal spatial frequency see an illusory grating of low spatial frequency, even when the spatial frequency of the fringes exceeds the resolution limit. This grating is a product of nonlinear distortion within the visual system [MacLeod, Williams and Makous (1992) Vision Research, 32, 347-363]. By separately manipulating the spatial frequencies of the interference fringes and the distortion gratings, we decomposed the contrast sensitivity function into two serial components separated by the nonlinear process. Losses in the optics of the eye were avoided by use of laser interferometry. Spatial summation preceding the nonlinear stage was restricted to the light-collecting area of individual cones and was directly proportional to the diameters of cone inner segments at three retinal eccentricities; this suggests that light is trapped within cones at the level of their inner segments. Even 30 degrees from the fovea, the nonlinear stage precedes the site where separate signals from individual cones are no longer maintained; this leads us to suggest that the nonlinear process lies within the retina. In addition, spatial antagonism precedes the nonlinear stage; this places the nonlinear process at a site following the outer segments of the cones. Dichoptic presentation of the interference fringes failed to produce illusory gratings; that is, the nonlinearities within the binocular pathway do not produce distortions like those produced by the monocular nonlinearity.

Contrast Sensitivity↗
PubMed1992

Qualitative holographic study of hemi-pelvic deformation caused by loading different hip prostheses.

The dynamic biological response of bone can materially influence the longevity of artificial implants. This paper presents a series of in vitro experiments conducted on epoxy resin models of human hemi-pelves. Different commercially available acetabular components were implanted and used for the construction of simplified three-dimensional models of the artificial hip joint. Boundary conditions included simulation of muscle groups and femoral loading. Real-time holographic interferometry, a stress analysis technique permitting whole-field simultaneous inspection of deformation patterns, was used as the experimental method. The holographic interferograms were interpreted qualitatively rather than quantitatively. High stresses were identified in the hemi-pelvis and it is postulated that these stresses may be implicated in the mechanical pathogenesis of loosening. The observed changes in the detected stress levels could influence both future design of acetabular prostheses and surgical techniques.

Biomechanical Phenomena↗
PubMed1980

Modes and waves in a cochlear model.

A simplified model hydroelastic system having many features in common with the cochlea is studied theoretically and experimentally. The system consists of a slender rigid tube filled with a viscous incompressible fluid. The tube is divided lengthwise into two chambers (scala vestibuli, scala tympani) by an interior surface, part of which is rigid and part elastic. The elastic portion is an isotropic plate having variable width and is clamped on its edges. The system is driven by a sinusoidal imput at the stapes end. The mechanical model is 24 times life size and dynamical similarity is maintained. Wave patterns in the plate are measured using time-averaged and stroboscopic holographic interferometry. At low frequency (corresponding to less than 500 cycles/s in the cochlea) the response can be adequately predicted by a one dimensional theory. The waves are a combination of traveling and standing waves. The traveling component is solely a dissipative effect. Discrete resonances are readily observed in the low frequency range.

Cochlea↗
PubMed1986

Directional hearing in the grassfrog (Rana temporaria L.). II. Acoustics and modelling of the auditory periphery.

In an earlier paper (Vlaming et al., 1984) we reported on optical measurements (laser-doppler interferometry) of the vibrations characteristics of the grassfrog's tympanic membrane. In the present paper these measurements were extended to include acoustic measurements concerning the functional role of the mouth cavity in frog hearing. Based on these measurements a model of the frog's acoustic periphery, consisting of three coupled linear oscillators with three entrance ports for sound, was developed and analyzed mathematically to give the various relevant transfer functions. The model is characterized by six parameters, all of which could be estimated from the available experimental data. For frequencies up to some 1500 Hz the model adequately describes the experimental data, both our own and earlier, seemingly conflicting data in the literature. For higher frequencies deviations occur, possibly due to nonuniform vibrations of the membranes. The model was used to evaluate the monaural directional sensitivity of the frog under free-field stimulation. Essentially it behaves as a combined pressure-gradient receiver, with highly frequency-dependent directional sensitivity. Directional sensitivity of the tympanic membrane could be modulated drastically by changing the resonance properties of the mouth cavity, without affecting the intrinsic membrane properties. This, theoretically, allows the frog to manipulate its direction sensitivity by actively tuning the volume of its mouth cavity. In order to account for discrepancies with known properties of low-frequency auditory nerve fibers an additional, extra-tympanic channel was included into the model. The extended model, the second-channel possibly involving the opercularis complex, provides a good quantitative fit to the available data on tympanic membrane movement as well as auditory nerve activity. Finally, the model enables to simulate a (moving) sound source in space, while stimulating the frog via closed couplers.

Acoustics↗
PubMed1986

Relationship between basilar membrane tuning and hair cell condition.

Basilar membrane tuning characteristics were measured in 15 cats using laser interferometry. The experimental procedures introduced varying degrees of cochlear trauma. Variability from animal to animal was also observed in the characteristic frequency (CF) of tuning, the sensitivity at CF and lower frequencies, and the sharpness of tuning. The changes in the tuning characteristics of the basilar membrane are correlated with the extent of outer hair cell (OHC) damage. These observations lead to the conclusion that the tuning properties in the CF region are predominantly determined by the mechanical properties of the OHC and not the basilar membrane.

Animals↗
PubMed1989

A temporal bone preparation for the study of cochlear micromechanics at the cellular level.

An in vitro preparation of the guinea pig temporal bone was developed for studying the micromechanical behaviour of the cochlea. The preparation consists of the cochlea opened at the apex, allowing observation of cellular structures within the cochlear partition with an optical sectioning microscope and measurements of cellular vibration with laser interferometry. The middle ear ossicles and the tympanic membrane are left intact as well as the bony part of the external auditory canal, which is used for delivering a sound stimulus to the cochlea.

Acoustic Stimulation↗
PubMed1993

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.

Animals↗
PubMed2004

Creating multiple time-shared laser traps with simultaneous displacement detection using digital signal processing hardware.

We present a design for implementing multiple laser traps for single-molecule studies through time-sharing using commercially available digital signal processing hardware in a computer running a standard multitasking operating system. This design enables four to six independent laser traps with a visitation frequency of 10,000s(-1)trap(-1) and a timing jitter of +/-0.5 micros to be created. The design also achieves nanometer-resolution detection of displacement in all of the traps simultaneously via back focal-plane interferometry and only a single quadrant photodiode detector. Practical design considerations and limitations together with the use of fiberlasers in laser traps are discussed. Using this device, the mechanokinetics of multiple molecular motors or adhesion proteins may be measured simultaneously. We present the example biological application of two kinesin-coated beads in separate traps moving on different portions of a microtubule.

Equipment Design↗
PubMed2006

Comparison of three methods of measuring corneal thickness and anterior chamber depth.

PURPOSE: To compare three different methods of measuring corneal thickness (CT) and anterior chamber depth (ACD). DESIGN: Prospective clinical trial (Medical University of Vienna, Austria). METHODS: Central CT (CCT), CT at four peripheral points, and central ACD were measured in 88 eyes of 44 healthy subjects with the Pentacam (rotating Scheimpflug camera; Oculus, Wetzlar, Germany), Orbscan I (scanning-slit topography system; Orbtek Inc, Salt Lake City, Utah, USA), and AC-Master (partial coherence interferometry; Zeiss Meditec, Jena, Germany), and the results were compared. RESULTS: The upper (lower) limits of agreement for CCT measurements were 7.9 (-22.2) microm between AC-Master and Pentacam, 17.6 (-32.5) microm between AC-Master and Orbscan, and 25.2 (-25.9) microm between Pentacam and Orbscan. Correlation was high between all three methods (r = 0.94 to 0.97). The upper and lower limits of agreement for ACD were 0.174 (-0.251) mm between AC-Master and Pentacam, 0.406 (-0.004) mm between AC-Master and Orbscan, and 0.384 (0.095) mm between Pentacam and Orbscan. Correlation was high between the three methods (r = 0.96 between Orbscan and Pentacam; others 0.92). Correlation was lower for the CT measurements at the four peripheral points. CONCLUSIONS: The CCT and ACD values obtained by Pentacam, Orbscan, and AC-Master measurements correlated well and showed few outliers. The two new systems (Pentacam, AC-Master) provide a reliable, easy-to-use, noncontact method of measuring CCT and ACD. Larger differences occurred only when measuring peripheral CT values, especially between AC-Master and the other two methods.

Adult↗
PubMed2005

[3D evaluation and mammary augmentation surgery].

The medical application of the interferometry is valid now. The breast surgery works on the shape and the volume of the tissue. The Inspeck technology is now available and works well in our medical practice. The measurement tools for the lengths, euclidian or projected on surface are working well with the same precision of a manual measurement. The estimation of the volume needs to follow exactly the same procedure to get some good results. The virtual breast modification doesn't work anymore with a scientific precision and does not allowed yet an office use. A development of the software is necessary to use all these data enclosed in the 3D models.

Adult↗
PubMed2004

Thermal and cold neutron phase-contrast radiography.

In this paper, we will discuss a phase-contrast imaging method that avoids the complications of interferometry to provide phase contrast in weakly absorbing samples. A transversely coherent neutron beam is used with the traditional radiography scheme. Images taken with this scheme show dramatic intensity variations due to sharp changes in the neutron wave refractive index. With some numerical processing these images may be used to reconstruct a quantitative phase radiograph of specimens imaged with this technique.

Journal Article↗
PubMed2004

Apolipoprotein E isoprotein-specific interactions with tissue plasminogen activator.

Apolipoprotein E (Apo E) is an important genetic risk factor for multiple neurological, vascular and cardiovascular diseases. Previously, we reported Apo E isoprotein-specific modulation of tissue plasminogen activator (tPA) using an in vitro blood-clotting assay. Here, we studied the conformational changes of Apo E2, E3 and E4 in the presence of tPA and vice versa using circular dichroism (CD) and dual polarization interferometry (DPI). We report isoprotein and state-specific intermolecular interactions between the Apo E isoforms and tPA. Apo E2 interaction with immobilized tPA leads to significant conformational changes which are not observed with Apo E3 or E4. Additionally, tPA induces changes in helicity of lipidated Apo E2 whereas no detectable changes were observed in Apo E3 or E4. The Tukey's test for interaction indicated a significant (P < 0.001) interaction between tPA and Apo E2 in the lipidated environment. These results may be important regarding the mechanism by which Apo E has isoprotein-specific effects on many biological processes and diseases involving blood clotting, proteolysis and perfusion.

Apolipoproteins E↗
PubMed2006

Biomimetic implant coatings.

Biomaterials and tissue engineering technologies are becoming increasingly important in biomedical practice, particularly as the population ages. Cellular responses depend on topographical properties of the biomaterial at the nanometer scale. Structures on biomaterial surfaces are used as powerful tools to influence or even control interactions between implants and the biological system [; ]. The influence of nanometer sized surface structures on osteoblastlike cell interactions was tested with niobium oxide coatings on polished titanium slices (cp-Ti grade 2). The aim of the study was to investigate the influence of nanoscopic surface structures on osteoblast interactions in order to support collagen I production and cell adhesion. The coatings were done by means of the sol-gel process. The surface structure was adjusted by annealing of the metaloxide ceramic coatings due to temperature depended crystal growth. The applied annealing temperatures were 450, 550 and 700 degrees C for 1 h, corresponding to Ra-numbers of 7, 15 and 40 nm. The surfaces were characterized by means of AFM, DTA/TG, diffractometry and white light interferometry. The cell reactions were investigated concerning adhesion kinetics, migration, spreading, cell adhesion, and collagen I synthesis. The smooth surface (Ra=7 nm) resulted in the fastest cell anchorage and cell migration. The closest cell adhesion was reached with the surface structure of Ra=15 nm. The roughest surface (Ra=40 nm) impedes the cell migration as well as a proper spreading of the cells. The best results concerning cell adhesion and spreading was reached with an intermediate surface roughness of Ra=15 nm of the niobium oxide coating on cp-titanium slices.

3T3 Cells↗
PubMed2005

In vivo cytokine secretion and NF-kappaB activation around titanium and copper implants.

The early biological response at titanium (Ti), copper (Cu)-coated Ti and sham sites was evaluated in an in vivo rat model. Material surface chemical and topographical properties were characterized using Auger electron spectroscopy, energy dispersive X-ray spectroscopy and interferometry, respectively. The number of leukocytes, cell types and cell viability (release of lactate dehydrogenase) were determined in the implant-interface exudate. The contents of activated nuclear transcription factor NF-kappaB, interleukin-6 (IL-6) and interleukin-10 (IL-10) were determined by enzyme linked immunosorbent assay. An increase in the number of leukocytes, in particular, polymorphonuclear leukocytes, was observed between 12 and 48 h around Cu. A marked decrease of exudate cell viability was found around Cu after 48 h. The total amounts of activated NF-kappaB after 12 h was highest in Ti exudates whereas after 48 h the highest amount of NF-kappaB was detected around Cu. The levels of cytokine IL-6 were consistently high around Cu at both time periods. No differences in IL-10 contents were detected, irrespective of material/sham and time. The results show that materials with different toxicity grades (titanium with low and copper with high toxicity) exhibit early differences in the activation of NF-kappaB, extracellular expression and secretion of mediators, causing major differences in inflammatory cell accumulation and death in vivo.

Animals↗
PubMed2006

In vitro studies of annulus fibrosus disc cell attachment, differentiation and matrix production on PDLLA/45S5 Bioglass composite films.

The aim of this study was to investigate the potential of using PDLLA/45S5 (PDLLA--poly(D,L-lactide)) Bioglass composite films for the culture of annulus fibrosus (AF) cells in vitro with a view to a tissue engineering application. PDLLA films incorporated with different percentages (0, 5 and 30 (wt%)) of Bioglass particles were prepared by solvent casting and characterized by scanning electron microscopy (SEM), water contact angle and white-light interferometry. Bovine AF cell morphology and attachment were analysed using SEM. Cytoskeletal organization was determined by actin labelling with FITC-phalloidin using fluorescence microscopy. The amount of sulphated glycosaminoglycan (sGAG) and collagen produced by AF cells were quantified using the 1,9-dimethylmethylene blue (DMMB) and Sircol assays after 4 weeks in culture. Composite films of PDLLA filled with Bioglass are an appropriate substrate for annulus cells and these films promote the production of an extracellular matrix (ECM) containing abundant sGAGs and collagen. These findings provide a basis for the understanding of the production of ECM molecules by cells cultured on 2D PDLLA/45S5 Bioglass composite films. The results will provide new insights into the design and development of composites containing Bioglass and resorbable polymers as scaffolds for intervertebral disc tissue repair.

Animals↗