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At least 181 records · Page 10Linked to original sources
PubMed1994

Measurement of elastic modulus of the central bovine cornea by means of holographic interferometry. Part II. Results.

BACKGROUND: The structural and elastic properties of the cornea play an important role in the outcome of corneal refractive surgery. A way to describe the elastic properties is to calculate Young's modulus. The tangent Young's modulus (Eit) represents the first part of the viscoelastic response of the intact cornea due to intraocular pressure increase. METHOD: The tangent Young's modulus (Eit) of the central cornea of 16 fresh enucleated intact bovine eyes determined from the immediate response was calculated by means of holographic interferometry. The stress was an increase of the intraocular pressure. In 16 eyes the change of intraocular pressure was 10 Pa (group I), starting with an intraocular pressure of 1340 Pa (about 10 mm Hg). In 6 of these 16 eyes there was a second pressure increase of 20 Pa starting at the same intraocular pressure of 1340 Pa (about 10 mm Hg) (group II). RESULTS: The mean value for the Young's modulus in group I was 1.58 x 10(5) Pa. For group II the Young's modulus was 1.60 x 10(5) Pa. The difference was not significant. The values for the Young's moduli of the cornea of intact eyes are about 100 times smaller than calculations based on experiments with strips of the cornea. CONCLUSION: It is necessary to consider the localization of the corneal tissue to avoid influences of corneal hydration or dehydration and to define the existing intraocular pressure if Young's modulus of the cornea is to be calculated.

Animals↗
PubMed2003

Laminectomy contributes to cervical spine deformity demonstrated by holographic interferometry.

Multiple factors contribute to the pathogenesis of postlaminectomy deformity and instability of the cervical spine. The complex alterations in both static and dynamic biomechanics after laminectomy are incompletely defined. We sought to examine the role of the lamina in compressive load bearing across the vertebral body. Holographic interferometry was used to study the surface deformation of single axially loaded cervical vertebral bodies before and after hemilaminotomy, hemilaminectomy, and experimental acrylic laminar reconstruction. Our results showed that hemilaminotomy did not alter the surface deformation because of axial loading across the cervical vertebral body. However, gross alterations in surface deformation across the cervical vertebral body were consistently observed after hemilaminectomy. Experimental reconstruction of the laminar arch using acrylic restored the deformation pattern to the prelaminectomized baseline. Our results support a role for the lamina and the integrity of the laminar arch in axial load bearing across the cervical vertebral body. The altered axial load bearing may be a significant contributor to postlaminectomy deformity and instability. These findings offer an additional biomechanical advantage to minimal bony intervention for cervical spine pathology.

Acrylic Resins↗
PubMed2004

Human middle ear transfer function measured by double laser interferometry system.

HYPOTHESIS: Simultaneous measurements of vibrations on the stapes footplate, incudostapedial (IS) joint, and tympanic membrane (TM) can be made in both normal and drained cochleae, and the stapes displacement transfer function (S-DTF) and TM displacement transfer function (TM-DTF) are derived. BACKGROUND: A single laser Doppler interferometer previously has been used for measuring movement of the stapes or TM in temporal bones. However, there may be a limitation to optimally describing acoustic-mechanical transmission when the interferometer and temporal bone are moved frequently during experimental recordings. Simultaneous measurements of vibrations of the TM and stapes footplate, or TM and IS joint may reveal different acoustic-mechanical characteristics of the middle ear. METHODS: Dual laser interferometers simultaneously measured vibrations of the TM, IS joint, and stapes in 10 temporal bones with both intact and drained cochleae. From these measurements, the middle ear transfer function was expressed as the S-DTF, TM-DTF, and displacement transmission ratio (DTR). RESULTS: Simultaneous displacements of the TM, IS joint, and stapes footplate induced by sound pressure in the ear canal were recorded in both amplitude and phase. The middle ear transfer functions in terms of displacement ratio confirmed published single interferometer data but provided new information from drained cochlea. CONCLUSION: Stapes and TM displacement transfer functions were determined using dual interferometry, provided accurate amplitude and phase relationships from stapes footplate, IS joint, and TM, with new data from drained and normal cochlea.

Acoustic Stimulation↗
PubMed2002

Measurement of x-ray pulse widths by intensity interferometry.

The pulse width of hard undulator radiation (32 ps width, energy 14 keV) was determined by intensity interferometry. The method, in combination with various x-ray monochromators, enables measurements to be taken over a wide range of time frames, from ns to fs. The applicable target includes measurements of ultrafast x-ray pulse widths from fourth generation synchrotron light sources.

Calibration↗
PubMed2002

Step bunching in a diffusion-controlled system: phase-shifting interferometry investigation of ferritin.

We present a novel phase-shifting interferometry technique for investigations of the unsteady kinetics and the formation of spatio-temporal patterns during the protein crystallization. We applied this technique to the ferritin crystal growth, which is controlled by the rate of supply of material. We find strong fluctuations of growth rate, step density and step velocity due to passage of step bunches. The fluctuation amplitudes decrease with higher supersaturation and larger crystal size, as well as with increasing distance from the step sources. Since these are parameters affecting the solute supply field, we conclude that fluctuations are rooted in the coupling of the interfacial processes of growth to the bulk transport in the solution. Analysis of the step velocity dependence on local slope indicates a very weak interaction between the steps. Hence, in diffusion-controlled systems with non-interacting or weakly interacting steps the stable growth mode is that via equidistant step trains, and randomly arising step bunches decay.

Animals↗
PubMed1991

Reconstruction of sequential cardiac in-plane displacement patterns on the chest wall by laser speckle interferometry.

Time-average speckle interferometry has been applied to obtain displacement patterns on the chest wall produced by cardiac action, in the absence of breathing, during various phases of the cardiac cycle. This has been achieved by an electronic shutter, controlled by the electrocardiogram of the subject. The recorded holographic plates processed under identical conditions are scanned by the pointwise method to obtain the absolute displacements at various locations corresponding to the activities of the various cardiac chambers and values. These data are transformed to a 40 x 30 matrix by an interpolation method and, from this, three-dimensional displacement plots are reconstructed by an IBM PC/AT computer. These patterns shown the displacements over the entire cardiac area corresponding to the activities of various regions during the cardiac cycle. The apex and aortic valve areas show the maximum displacements during the systolic phase. During the diastolic phase the activities over the low pressure atrial regions are also observed. The results obtained outline the functional details of the normal heart and the activities over various areas are in agreement with that of other noncontact techniques.

Algorithms↗
PubMed1991

Ultrasonic interferometry: study of particle sedimentation in liquid.

An ultrasonic interferometry method was designed to study sedimentation of particles in liquid. The method, based on A mode echography, measures the amplitude of ultrasonic waves reflected (echo E1) by a fixed interface I1 called "solid plate-sediment" interface formed when particles are sedimenting on a solid plate. The amplitude of the echo depends both on mechanical properties of the three media (solid plate, sediment and suspension) on the thickness of the sediment and on the presence of a second mobile interface I2 called "sediment-suspension" interface. In the first phase of sedimentation when the second interface is very close to the first, two reflected waves interfere. Then, in the second phase of sedimentation when the sediment is thick enough, the amplitude of the echo E1 depends only on the sediment and solid plate properties. The first phase will give information on the sedimentation rate of particles (SR). We have compared SR of particles determined by this method with SR measured in a cylindrical tube of the same geometry as the ultrasonic measurement cell and with theoretical values of the sedimentation rate given by theoretical models.

Interferometry↗
PubMed2000

In vitro simultaneous measurement of refractive index and thickness of biological tissue by the low coherence interferometry.

We proposed and demonstrated in vitro simultaneous measurement of refractive index and thickness of biological tissue. The technique is based on the low coherence interferometry combined with precise translation stages. Refractive indices were determined with the accuracy of less than 1% for tissue samples of a few hundred micron thickness, including chicken tissue, human tooth and nail. Simultaneous measurement of refractive index and thickness of multilayer tissue are also demonstrated.

Animals↗
PubMed2002

Vibration maps of capacitive micromachined ultrasonic transducers by laser interferometry.

In this letter, a 1.8-mm x 1.8-mm capacitive micromachined ultrasonic transducer (CMUT) element is experimentally characterized by means of optical measurements. Optical displacement measurements provide information on the resonant behavior of the single membranes and also allow us to investigate the dispersion in the frequency spectrum of adjacent membranes. In addition, higher order mode shapes are observed, showing that either symmetrical or asymmetrical modes are excited in CMUT membranes. Laser interferometry vibration maps, combined with quantitative displacement measurements, provide information about the quality and repeatability of the fabrication process, which is a basic requirement for 2-D array fabrication for ultrasound imaging.

Coated Materials, Biocompatible↗
PubMed2002

Measurement of the density of CO(2) solution by Mach-Zehnder interferometry.

The density of CO(2) solution was measured by using Mach-Zehnder interferometry in the pressure range from 5.0 to 12.5 MPa, at temperatures from 273.25 to 284.15 K, and CO(2) mass fraction in solution up to 0.061. It was found that the density difference between the CO(2) solution and pure water at the same pressure and temperature is monotonically linear with the CO(2) mass fraction. The slope of this linear function, calculated by experimental data fitting, is 0.275.

Carbon Dioxide↗
PubMed1981

Measurement of dimensional stability of elastomeric impression materials by holographic interferometry.

A technique for measuring changes in the dimensions of elastomeric impression materials is described. The technique involves using holographic interferometry to determine the rate of dimensional change on setting of the materials. The total change in dimension is found by integration with time. The sensitivity of the technique allows accurate determination of these quantities. Holography involves no direct physical contact with the test sample and more than one sample can be tested at the same time under the same conditions. In a preliminary investigation, the technique was applied to several classes of commercially available impression materials. The results are compared with those obtained by other techniques.

Dental Impression Materials↗
PubMed2001

Computer aided speckle interferometry: a technique for measuring deformation of the surface of the heart.

An investigation of the inhomogeneous and anisotropic properties of myocardium necessitates a whole field measurement technique with high spatial resolution. Computer aided speckle interferometry (CASI) may be applied to measuring deformation on the epicardial surface of the heart. Silicone carbide particles (approximately 40 microm in diameter) were sprinkled randomly onto the epicardial surface of isolated rabbit hearts. When illuminated with white light, speckles may be observed with a charge coupled device (CCD) camera. A balloon was placed in the left ventricle to control the intracavitary load on the arrested heart. To compare CASI to the "gold" standard technique of sonomicrometry, two ultrasonic transducers were implanted into the wall of the myocardium. Three hearts were exposed to various loading conditions, and at each condition speckle images were recorded. CASI was used to determine the distribution of displacement vectors (both direction and magnitude) in the region imaged by the CCD camera. Strain along the axis of the implanted transducers was determined with CASI and compared to that obtained with sonomicrometry. Strain determined from CASI and sonomicrometry produced equivalent results. Unlike sonomicrometry, whereby the displacement between two points with a relatively large gauge length is obtained, CASI is able to determine displacement vectors for hundreds of "points" within the same region. In conclusion, CASI produced equivalent results to those obtained from sonomicrometry (although not with the same temporal resolution), but it is a whole field deformation mapping technique that has a spatial resolution three orders of magnitude higher than that of sonomicrometry.

Animals↗
PubMedDate not supplied

Phase shifting speckle interferometry for determination of strain and Young's modulus of mineralized biological materials: a study of tooth dentin compression in water.

Mineralized biological materials have complex hierarchical graded structures. It is therefore difficult to understand the relations between their structure and mechanical properties. We report the use of electronic speckle pattern-correlation interferometry (ESPI) combined with a mechanical compression apparatus to measure the strain and Young's modulus of root dentin compressed under water. We describe the optomechanical instrumentation, experimental techniques and procedures needed to measure cubes as small as 1 x 1 x 2 mm. Calibration of the method is performed using aluminum, which shows that the measurements are accurate within 3% of the compression modulus reported for standard aluminum 6061. Our results reveal that the compression moduli of root dentin from the buccal and lingual sides of the root are quite different from the moduli of the interproximal sides. Root dentin from interproximal locations is found to have an average modulus of 21.3 GPa, which is about 40% stiffer than root dentin from the buccal and lingual locations, found to have a modulus of 15.0 GPa. Our approach can be used to map deformations on irregular surfaces, and measure strain on wet samples of varying sizes. This can be extended to the study of other biological materials including bone and synthetic biomaterials.

Compressive Strength↗
PubMedDate not supplied

Surface plasmon resonance phase-shift interferometry: real-time DNA microarray hybridization analysis.

Surface plasmon resonance (SPR) phase-shift interferometry (PSI) is a novel technique which combines SPR and modified Mach-Zehnder PSI to measure the spatial phase variation caused by biomolecular interactions upon a sensing chip. The SPR-PSI imaging system offers high resolution and high-throughout screening capabilities for microarray DNA hybridization without the need for additional labeling, and provides valuable quantitative information. The SPR-PSI imaging system has an enhanced detection limit of 2.5 x 10(-7) refraction index change, a long-term phase stability of pi/100 in 30 min, and a spatial phase resolution of pi/300 with 100 x 100 microm2 detection area. This study successfully demonstrates the label-free observation of 15-mer DNA microarray.

DNA↗
PubMedDate not supplied

Prospective grading of neoplastic change in rat esophagus epithelium using angle-resolved low-coherence interferometry.

Angle-resolved low-coherence interferometry (a/LCI) is used to obtain quantitative, depth-resolved nuclear morphology measurements. We compare the average diameter and texture of cell nuclei in rat esophagus epithelial tissue to grading criteria established in a previous a/LCI study to prospectively grade neoplastic progression. We exploit the depth resolution of a/LCI to exclusively examine the basal layer of the epithelium, approximately 50 to 100 microm beneath the tissue surface, without the need for exogenous contrast agents, tissue sectioning, or fixation. The results of two studies are presented that compare the performance of two a/LCI modalities. Overall, the combined studies show 91% sensitivity and 97% specificity for detecting dysplasia, using histopathology as the standard. In addition, the studies enable the effects of dietary chemopreventive agents, difluoromethylornithine (DFMO) and curcumin, to be assessed by observing modulation in the incidence of neoplastic change. We demonstrate that a/LCI is highly effective for monitoring neoplastic change and can be applied to assessing the efficacy of chemopreventive agents in the rat esophagus.

Animals↗
PubMedDate not supplied

Measurement of dye diffusion in scattering tissue phantoms using dual-wavelength low-coherence interferometry.

We demonstrate low-coherence interferometry (LCI) for dye diffusion measurements in scattering tissue phantoms. The diffusion coefficient of a phthalocyanine dye in 1.5% agar gel containing scattering Intralipid was measured using a dual-wavelength interfero-meter. One wavelength was matched to the absorption peak of the dye at 675 nm. The other, 805 nm, was not affected by the dye, and was used to correct for varying sample scattering as a function of depth, assuming a constant ratio between scattering at the two wavelengths. The same wavelength dependence of scattering is assumed for the entire sample, but no a priori knowledge about the amount of scattering is needed. The dye diffusion coefficient was estimated by fitting a mathematical model of the interferometer signal to the measured LCI envelope. We compare results obtained using both a constant-scattering and a depth-resolved-scattering approach to determine the sample scattering. The presented method provides robust estimation of the diffusion coefficient when spatial resolution in determining the depth-resolved scattering is varied. Results indicate that the method is valid for samples having continuous spatial variations in the scattering coefficient over lengths as short as the coherence length of the probing light. The method allows in situ characterization of diffusion in scattering media.

Animals↗
PubMedDate not supplied

Label-free measurement of microbicidal gel thickness using low-coherence interferometry.

Spectral-domain low-coherence interferometry (LCI) was used to measure the thickness of microbicidal gels applied to a cylindrical calibration test socket. Microbicides are topical formulations containing active ingredients targeted to inhibit specific pathogens that are currently under development for application to the epithelial lining of the lower female reproductive tract to combat sexually transmitted infections such as HIV. Understanding the deployment and drug delivery of these formulations is vital to maximizing their effectiveness. Previously, in vivo measurements of microbicidal formulation thickness were assessed using fluorescence measurements of fluorescein-labeled gels via an optical endoscope-based device. Here we present an LCI-based device that measures the thickness of a formulation without the use of any exogenous agents by analyzing the interference pattern generated between the reflections from the front and back surface of the sample. Results are presented that validate the effectiveness and performance of the LCI measurement in a clinically relevant system as compared to an existing fluorescence-based method. The impact of the new LCI-based design on in vivo measurements is discussed.

Anti-Infective Agents↗
PubMedDate not supplied

Analysis of long range correlations due to coherent light scattering from in-vitro cell arrays using angle-resolved low coherence interferometry.

Angle-resolved low coherence interferometry (a/LCI) enables depth-resolved measurements of scattered light that can be used to recover subsurface structural information, such as the size of cell nuclei. Measurements of nuclear morphology, however, can be complicated by coherent scattering between adjacent cell nuclei. Previous studies have eliminated this component by applying a window filter to Fourier transformed angular data, based on the justification that the coherent scattering must necessarily occur over length scales greater than the cell size. To fully study this effect, results of experiments designed to test the validity of this approach are now presented. The a/LCI technique is used to examine light scattered by regular cell arrays, created using stamped adhesive micropatterned substrates. By varying the array spacing, it is demonstrated that cell-to-cell correlations have a predictable effect on light scattering distributions. These results are compared to image analysis of fluorescence micrographs of the cell array samples. The a/LCI results show that the impact of coherent scattering on nuclear morphology measurements can be eliminated through data filtering.

Algorithms↗