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At least 37 records · Page 2Linked to original sources
PubMed1993

Preoperative evaluation by laser interferometry in cataractous eyes with retinitis pigmentosa.

Measurements of visual acuity were carried out preoperatively by laser interoferometry in 16 cataractous eyes of 13 patients with retinitis pigmentosa who were older than 60 years of age. Subsequently, all patients underwent uneventful extracapsular cataract extraction and posterior chamber intraocular lens implantation. Postoperative visual acuity, which was evaluated as the best acuity during the first postoperative year, was improved in all eyes and it correlated well with the preoperative acuity determined by laser interferometry. Laser interferometry can be useful in predicting postoperative acuity and deciding on cataract surgery for elderly cataractous patients with retinitis pigmentosa.

Aged↗
PubMed1996

Quality control of bioprosthetic heart valves by means of holographic interferometry.

BACKGROUND AND AIMS OF THE STUDY: Limited durability of porcine bioprostheses is mainly caused by the progressive development of calcification. We tested the hypothesis that hidden tissue anomalies or unfavorable stress concentrations of commercially available bioprostheses may lead to later calcification and dysfunction. Application of holographic interferometry for non-destructive testing of biological heart valves enables a full-field analysis of heart valves and reveals deformation irregularities of valve tissue. MATERIAL AND METHODS: We developed an accelerated calcification protocol for bioprosthetic heart valves including an accelerated pulsatile valve tester for simultaneous testing of 10 heart valves under identical conditions and a rapid synthetic calcification fluid containing a final Ca x P of 130 (mg/dl)2 in barbital buffer solution. Ten porcine bioprostheses (St. Jude Medical, Bioimplant) were assessed by holographic interferometry and subjected to the pulsatile accelerated calcification process. Distribution and amount of calcification was evaluated by microradiography after 12 x 10(6) and 19 x 10(6) cycles, respectively. Areas of irregular fringe patterns detected by holography as well as areas of calcification were calculated and compared using a personal computer. RESULTS: All tested bioprostheses had localized or extended areas with holographic irregularities and the accelerated valve testing protocol resulted in even macroscopically visible calcifications at various sites. Comparative analysis of the obtained microradiographs revealed that 74.2% +/- 6.0% of calcified leaflet areas lay within the previously detected holographic anomalies. CONCLUSIONS: Our first results show a strong correlation between holographic anomalies and calcification of porcine bioprostheses. We conclude that suitable methods for evaluation and quality control of bioprosthetic heart valves are available and seem to be predictive with regard to valve calcification.

Aortic Valve↗
PubMed1997

Implantable hearing device performance measured by laser Doppler interferometry.

Recent application of the Doppler principle laser interferometry to audiology, acoustics and otology has facilitated the development of implantable hearing devices (IHDs). During the design and testing of two different electromagnetic middle ear implants for sensorineural hearing loss, we used single-point laser Doppler interferometry (LDI). A commercially available interferometer, internally calibrated and validated against a National Institute for Standards and Technology (NIST) standard, was used with both mechanical fixtures and fresh temporal bones to evaluate implant mass, shape and orientation, attachment, electromagnetic coupling and acoustic properties. At both Hough Ear Institute and Symphonix Devices, Inc., we have shown that high fidelity and amplitudes can be recorded in vitro over a frequency range of 500 Hz to 10 kHz. These data can provide greater assurance of safety and efficacy to regulatory agencies before entering clinical trials. We propose that LDI be considered as an international standard for accurate, consistent comparison of performances of all IHDs during development. Furthermore, the future availability of human IHD data will allow for the extrapolation of a mechanical bench model of the middle ear transfer function for use in quality control during manufacturing and diagnosis of failure in IHDs.

Cochlear Implants↗
PubMed1987

Evaluation of double-exposure holographic interferometry for biomechanical measurements in vitro.

Double-exposure holographic interferometry is a nondestructive testing technique for measuring displacement and strain in a test object. A standard hologram contains three-dimensional information about an object. However, the holographic interferogram has additional information, as a series of interference bands overlaid on the three-dimensional image of the object contains information about object deformation. Interferograms were produced for intact cadaveric femora and cadaveric femora with implanted titanium alloy and cobalt-chromium alloy femoral components. A force was applied to the femoral head to simulate single leg stance, and changes in specimen deformation were observed as additional incremental loads were applied. We have observed that the femur behaves as a bending beam and that the holographic technique allows the position of maximal deflection to be identified and the magnitude of femoral displacement from the load axis to be determined at any point within the field of view. The effects of the modulus of the implanted stem on the bending characteristics of the composite structure were clearly seen in the interferograms. This communication presents a photographic analysis of the double exposure interferograms recorded, as well as a critique of the technique for biomechanical measurements in vitro.

Biomechanical Phenomena↗
PubMed1995

Determination of local refractive index for protein and virus crystals in solution by Mach-Zehnder interferometry.

To establish the importance of, and quantitatively evaluate, the macromolecular concentration gradients in the neighborhood of growing protein, virus, and nucleic acid crystals, a convenient, accurate, and nonintrusive method has been devised. This approach should prove particularly relevant in the rigorous comparison of crystals grown in a conventional laboratory setting with those grown in a microgravity environment. The method is based on precise determination of the local refractive index using Mach-Zehnder interferometry. Presented here are data for five protein and three virus systems. From data for these and other systems, optical monitoring experiments to measure local growth conditions and growth kinetics in liquid-liquid diffusion, batch, and vapor diffusion crystal growth experiments can be designed.

Interferometry↗
PubMed1994

In vivo imaging of the interior of Tradescantia zebrina leaves by optical cross-correlation interferometry.

Using optical correlation interferometry, a novel method for plant sciences, we in imaged in vivo the z-direction, perpendicular to the leaf surface, through Tradescantia zebrina leaves. Non-invasively we determined number of major cell layers, followed the time sequence of decrease in cell z-axis after exposure of tissues to high salt, and observed disruption of cells caused by freezing and thawing.

Interferometry↗
PubMed1993

Biomechanical investigation of the hyoid bone using speckle interferometry.

Speckle interferometry is a non-destructive measurement technique using a laser. The principles of the method are described. Human hyoid bones (n = 10) were investigated. Loads were applied to individual points on the anterior surface of the body of hyoid bones. All hyoid bones showed an asymmetric displacement. The displacement was greatest in a plane vertical to the load. An evaluation of fracture behavior is possible due to the displacement pattern.

Adult↗
PubMed1990

Holographic interferometry in the biomechanical study of femoral behavior, with and without prosthesis.

The authors studied the strains acting on a normal femur, and on the same femur fitted with an uncemented screwed prosthesis, by means of the method of holographic interferometry. This modern optical method has the advantage of not requiring any preparation of the surfaces or modification of the bone to be studied. It is non-destructive and can be repeated. This study required 40 interferograms for each case, using two or even three views. Comparison of the images obtained showed major modifications: disappearance of the physiologic flexion of the diaphysis, overload of the upper third, and zones of excess constraint.

Biomechanical Phenomena↗
PubMed1995

Preliminary study of the human lumbar spine using speckle technique. Limits of compression, shear and torsion. Speckle photography--electronic speckle pattern interferometry.

Optical techniques using single wavelength lasers allow precise study of the superficial displacements of deeper anatomical structures through direct mechanical pull. Two techniques have been used in this study: 1. Double exposure speckle photography. Since 1980 the relationship between the surface displacements and minimal traction applied to the transverse processes of the spine, either unilateral or bilateral, was studied in an attempt to simulate muscular action exerted at this level. 2. Computerised speckle interferometry. This allowed analysis of the deformations between the lumbar vertebrae under vertical compression, shear or torsion outside the usual anatomical planes. This preliminary study outlines the mechanical behaviour and the plasticity of the vertebral structures but has been performed on only a few anatomical specimens thus not allowing statistical analysis. This would require a larger series.

Biomechanical Phenomena↗
PubMed1985

Study of the mandible under static constraints by holographic interferometry. New biomechanical deductions.

In order to try to determine the nature of the mechanical structure of the mandible, the authors have compared, with the help of holographic interferometry, the behavior of the fresh mandible of a corpse, of a representative iron angle, and of a block of carbon-carbon under static constraint. There are no similarities between the behavior of the human mandible and that of a polycrystalline steel. On the contrary, the behavior of the mandible and of the carbon-carbon block are very similar. It would be hasty to state that bones are a heterogeneous composite. We can only prove, in a first approach, that they behave similarly under identical experimental conditions. The authors also demonstrated that the mandible presents a "mechanical hysteresis" phenomenon. This means that, when subjected to a small strain, its shape changes, but this change tends to neutralize itself in part in the course of time.

Aged↗
PubMed1987

Holographic interferometry: a critique of the technique and its potential for biomedical measurements.

Double-exposure holographic interferometry is a contactless whole-field method. Dimensional changes are visualized as a series of interference fringes overlaid on the holographic image of the femur, where each fringe represents 0.316 micron (half the wavelength of the laser light) of motion. Interferograms for intact femora and for femora with identical geometry prostheses were produced. We have shown that the femur bends as a beam under axial load. The position of maximum deflection is a function of the properties of the composite structure. Under a known load the amount of deflection can be calculated and the effect of the prosthesis's modulus can be ascertained. In addition to bending, rotational effects can be perceived. Although data interpretation is complex and holographic production is costly and time-consuming, the technique holds promise for biomechanical applications as well as other biomedical disciplines.

Biomechanical Phenomena↗
PubMed1989

Three-dimensional reconstruction of cardiac displacement patterns on the chest wall during the P, QRS and T-segments of the ECG by laser speckle interferometry.

A noninvasive and noncontact technique based on the principle of laser speckle interferometry has been developed to record the cardiac displacements observed on the chest wall. These displacements are then reconstructed in the form of three-dimensional plots, during the P, QRS and T-waves of the ECG. A comparison of these patterns shows that the mechanical activity of each region varies significantly during these phases of cardiac cycle. As these displacements depend on the clinical status of the heart, its use with a cardiac patient shows the functional changes of the affected regions in the form of alteration of these patterns.

Electrocardiography↗
PubMed1981

The effects of class II elastic force on a dry skull measured by holographic interferometry.

A method was developed for measuring bone displacements due to orthodontic forces. By means of holographic interferometry, the effects of Class II elastics on a dry skull were investigated. The bone deformation induced by the elastic force was studied on double-exposed holograms and also by the live fringe method. The results of this study reveal that sutures in the skull behave as weak structures, creating an interruption in the fringe pattern. With regard to the nasofrontal suture, the main movement, as could be expected, was an anteroposterior displacement. Related to the first molar, chosen as the anchorage unit, the vertical displacement was most pronounced. Furthermore, according to the findings of this study, the zygomaticotemporal suture was behaving as a hinge axis in a transversal direction. The method developed seems to be suitable for measuring bone displacements qualitatively as well as quantitatively.

Adult↗
PubMed1992

Flexion characteristics of four-unit fixed partial denture frameworks using holographic interferometry.

Flexion of a metal/ceramic fixed partial denture (FPD) framework under function can cause fracture of the porcelain or deterioration of the cement seal. This study evaluated the flexion under compressive load of a four-unit mandibular FPD replacing the second premolar and the first molar. Testing was accomplished with elapsed time holographic interferometry, using 39 porcelain fused-to-metal frameworks cast with a silver-palladium alloy. The results demonstrated that solder joints at the junction of the premolar and molar pontics flexed under a reduced compressive load and exhibited a higher failure rate than other connector designs.

Analysis of Variance↗
PubMed1993

Load transmission evaluation by removable distal-extension partial dentures using holographic interferometry.

Five pairs of bilateral distal-extension removable partial dentures with different clasp designs were constructed on the same dried human mandible in order to compare their load distribution characteristics. The technique of holographic interferometry was used. Among the dentures tested, those with RPI and back action clasps having mesial rests provided the best results from the mechanical point of view. The most unfavourable behaviour was presented by the Akers clasps design. The RPA design and dentures having clasps with continuous MOD rest gave intermediate results.

Dental Clasps↗
PubMed1996

The vibration pattern of the hearing organ in the waltzing guinea-pig measured using laser heterodyne interferometry.

The mechanical tuning characteristics of the hearing organ were measured in response to sound stimulation using laser heterodyne interferometry in in vitro preparations of temporal bones from waltzing guinea-pigs expressing different degrees of hearing organ and sensory cell degeneration. Measurements were made at various stages of structural changes allowing us to correlate structure and mechanical function. It was found that the characteristic frequency of the response at a given location in the cochlea occurred at lower frequencies than what is normally seen and that the sharpness of the mechanical tuning was considerably reduced when sensory hair cells were absent and the hearing organ structurally altered. However, even when extensive hair cell degeneration was evident a residual mechanical tuning was present. These results further support the concept that the sensory hair cells plays a key role in determining normal auditory tuning characteristics. It is suggested that the basilar membrane mechanics gives rise to a broadly tuned mechanical response on which a sharper tuning mechanism, originating from the hair cells, is superimposed.

Acoustic Stimulation↗
PubMed1996

Measurement of human platelet microaggregates by a new method: ultrasonic interferometry.

We have adapted the ultrasonic interferometry technique (Echo-Cell), which was initially designed to study red blood cell aggregation and agglutination, to the detection of human platelet microaggregates. The experimental parameter chosen was the slope of the signal over the first 5 minutes of sedimentation. We compared our new method with the conventional aggregometry for the measurement of aggregates after thrombin-, collagen-, and epinephrine-induced platelet activation. Under these conditions we demonstrated the particular sensibility of the present method in detecting small platelet aggregates induced in the first phase of aggregation and formed by low concentrations of agonists. Furthermore, as an illustration of this method, we showed an inhibition of the formation of thrombin-induced platelet aggregates in a concentration-dependent manner by the well known antagonist arginine-glycine-aspartic acid-serine with a median inhibitory concentration of 0.4 micromol/L, which is 30 times lower than the median inhibitory concentration found by aggregometry.

Blood Platelets↗