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At least 451 records · Page 25Linked to original sources
PubMed2006

The protective effect of TiF4, SnF2 and NaF on erosion of enamel by hydrochloric acid in vitro measured by white light interferometry.

The purpose of this in vitro study was to compare the protective effect of TiF4, SnF2 and NaF (all 0.5 M F) on the development of erosion-like lesions in human dental enamel. Four enamel specimens from each of 6 extracted molars were polished and embedded in epoxy resin. The enamel surfaces of 3 specimens from each tooth were treated with the different fluoride solutions for 2 min. Following fluoride treatments, the specimens were immersed in 0.01 M HCl (pH 2.0), for 2, 4 and 6 min in order to mimic a gastric reflux situation. One specimen from each tooth was used as a control and was only exposed to acid. The etching depths (in micrometres) after 6 min were: TiF4 0.8 (SD 0.8), SnF2 3.5 (SD 0.7), NaF 5.3 (SD 0.4), and 7.0 (SD 0.3) for the control specimens. Compared to the control, TiF(4) protected the enamel surface from acid attack almost completely (88%), while SnF2 reduced the etch depth after 6 min by 50% and NaF by 25%.

Analysis of Variance↗
PubMed2003

Thickness of the pre- and post-contact lens tear film measured in vivo by interferometry.

PURPOSE: To evaluate an interferometric method for measuring the thickness of the pre- (PLTF) and postlens tear film (POLTF) in subjects wearing hydrogel contact lenses. The precision and accuracy of measuring postlens tear thickness is compared with a previous method based on optical pachymetry and mechanical measurement of contact lens thickness. METHODS: Reflectance spectra (562-1030 nm) from the front of an eye wearing a contact lens were measured at normal incidence. Interference between reflections from four surfaces--the front of the tear film, the front and back of the contact lens, and the front of the cornea--can give rise to as many as six oscillations in the reflectance spectra, three from simple layers (layer A: PLTF; B, POLTF; C, contact lens) and three from composite layers, (layer D, A+C; layer E, C+B; layer F, A+C+B). The thickness of any layer is derived from the frequency of the oscillations. The principle of the method was tested with a rigid contact lens, which was designed to give distinct thicknesses for all six layers. Twenty spectra were then recorded from each of 12 subjects wearing hydrogel contact lenses. RESULTS: The PLTF thickness averaged 2.31 microm. There was good agreement between a direct estimate from layer A and an indirect estimate: layer D minus layer C. For POLTF, an indirect estimate--layer F minus layer D--averaged 2.34 microm and was more satisfactory than the direct estimate from layer B. There was no correlation between PLTF and POLTF thickness, showing that these are independent measurements, despite the similarity of their means. CONCLUSIONS: Prelens tear thickness was in reasonable agreement with prior measurements. Postlens tear thickness was much less than the 11 to 12 microm found by the pachymetric method. It is argued that the current method avoids some of the systematic errors of the pachymetric method and also has much higher precision.

Adult↗
PubMed2002

Liquid-crystal adaptive optics based on feedback interferometry for high-resolution retinal imaging.

A novel, to our knowledge, adaptive optical imaging system for high-resolution retinal imaging is described. The system is based on a feedback interferometer, in which two-dimensional output fringe intensity from a Mach-Zehnder interferometer with large radial shear is fed back, with the help of a video projector connected with a CCD camera, to an optically addressed phase-only liquid-crystal spatial light modulator. Experiments to verify the system performance have been conducted by use of an artificial eye consisting of a lens, an aberration plate, and a resolution test target. We observed that an image of the test target (mimicking a retina) blurred by the aberration plate (mimicking ocular aberrations) was successfully restored immediately after our adaptive optics system was activated.

Eye, Artificial↗
PubMed2005

Coherence-contrast x-ray imaging based on x-ray interferometry.

Coherence-contrast x-ray imaging--which detects changes in the degree of coherence caused by the placement of a sample in an x-ray interferometer--was developed for biomedical applications. Because the technique's sensitivity depends on the density gradient in the sample, it is particularly suitable for observing biomedical samples with large density differences, such as samples that include both biological soft tissue and bone. A measurement principle and method of this technique are described, and a fine coherence-contrast image of a mouse leg is given as an example result.

Animals↗
PubMed2006

Computational hyperspectral interferometry for studies of brain function: proof of concept.

Hyperspectral interferometric microscopy uses a unique combination of optics and algorithm design to extract information. Local brain activity rapidly changes local blood flow and red blood cell concentration (absorption) and oxygenation (color). We demonstrate that brain activity evoked during whisker stimulation can be detected with hyperspectral interferometric microscopy to identify the active whisker-barrel cortex in the rat brain. Information about constituent components is extracted across the entire spectral band. Algorithms can be flexibly optimized to discover, detect, quantify, and visualize a wide range of significant biological events, including changes relevant to the diagnosis and treatment of disease.

Animals↗
PubMed1993

Axial eye-length measurement by wavelength-shift interferometry.

A simplified noncontact measuring technique for axial eye length was developed. According to this method, the wavelength shift of a single-mode laser-diode beam that is irradiated onto the eyeball causes a phase shift in the interference fringes of reflections from the retina and the cornea. Then the optical distance between the cornea and the retina is obtained from the phase-shift measurement. High-speed axial eye-length measurements can be performed by using a laser diode on a pulse-modulation drive and signals from the reference light path as an analog-to-digital-conversion trigger. Compared with the technique that uses partially coherent light, this technique is inferior in terms of measurement accuracy but superior in its wide, measurable range of 16-32 mm. The results of measurements of 21 adults showed that 2 standard deviations of measurement was 2 sigma = +/- 0.11 mm.

Adult↗
PubMed2006

Optical tomography of transparent objects with phase-shifting interferometry and stepwise-shifted Ronchi ruling.

An experimental setup for tomographic inspection of phase objects is presented. The system uses a common-path interferometer consisting of two windows in the input plane and a translating grating as its pupil. In the output, interference of the fields associated with replicated windows is achieved by a proper choice of the windows' spacing with respect to the grating period. With a rotating object in one window and a plane wave in the second one, the phase distribution of each projection is encoded as a corresponding digital image row, which, in turn, constructs a composite interferogram over the plane of a traditional sinogram. Phase stepping of composite interferograms can be achieved by a proper translation of the grating in order to obtain the unwrapped phase distribution as the corresponding sinogram. This sinogram allows tomographic reconstruction of phase slices by standard procedures. Composite interferograms and reconstructions for some transparent samples are shown.

Equipment Design↗
PubMed2003

Fourier-domain low-coherence interferometry for light-scattering spectroscopy.

We present a novel method for obtaining depth-resolved spectra for determining scatterer size through elastic-scattering properties. Depth resolution is achieved with a white-light source in a Michelson interferometer with the mixed signal and reference fields dispersed by a spectrograph. The spectrum is Fourier transformed to yield the axial spatial cross correlation between the signal and reference fields with near 1-microm depth resolution. Spectral information is obtained by windowing to yield the scattering amplitude as a function of wave number. The technique is demonstrated by determination of the size of polystyrene microspheres in a subsurface layer with subwavelength accuracy. Application of the technique to probing the size of cell nuclei in living epithelial tissues is discussed.

Fourier Analysis↗
PubMed2004

Spinning-disk self-referencing interferometry of antigen-antibody recognition.

A gold ridge microstructure fabricated to a height of lambda/8 on a high-reflectivity substrate behaves as a wave-front-splitting self-referencing interferometer in phase quadrature when illuminated by a Gaussian laser beam and observed in the far field along the optic axis. When immuno-gammaglobulin (IgG) antibodies are selectively immobilized on the gold microstructure, they recognize and bind to a specific antigen, which shifts the relative optical phase of the interferometer and modifies the far-field diffracted intensity. We detect bound antigen interferometrically on spinning disks at a sampling rate of 100 kHz and verify the interferometric nature of the signal by using two quadratures of opposite sign to rule out effects of dynamic light scattering. Strong molecular recognition is demonstrated by the absence of binding to nontarget molecules but strong signal change in response to a specific antigen. This BioCD has the potential to be applied as a spinning-disk interferometric immunoassay and biosensor.

Animals↗
PubMed2006

Full-field quantitative phase imaging by white-light interferometry with active phase stabilization and its application to biological samples.

We report a Koehler-illumination-based full-field, actively stabilized, low-coherence phase-shifting interferometer, which is built on a white-light Michelson interferometer. By using a phase-stepping technique we can obtain full-field phase images of the sample. An actively stabilized phase-lock circuit is employed in the system to reduce phase noise. An application to human epithelial cells (HeLa cells) is achieved in our experiment. The advancement of this technique rests in its ability to take images of unstained biological samples quantitatively and on a nanometer scale.

Equipment Design↗
PubMed2006

Ultrasound and partial coherence interferometry with measurement of central corneal thickness.

PURPOSE: To compare noncontact pachymeter measurements with ultrasound pachymeter measurements and assess their reproducibility. METHODS: Central corneal thickness was measured in 104 eyes of 56 patients with three laser interference pachymeters (OLCR [Haag Streit, Könitz, Switzerland], OCP [4optics AG, Lübeck, Germany], and ACMaster [Carl Zeiss Meditec, Jena, Germany]) and an ultrasound pachymeter (Tomey AL2000 [Tomey Corp, Nagoya, Japan]). RESULTS: Compared to the ultrasound measurements, the mean difference for the laser interference pachymeter measurements were +8.8 microm (standard deviation [SD] 5.68) for the OLCR, -8.0 microm (SD 5.39) for the OCP, and -0.12 microm (SD 5.88) for the ACMaster. Reproducibility could only be estimated as not all of the devices allowed access to individual measurements. For all laser interference devices, reproducibility was estimated to be approximately 2 microm. Ultrasound measurements yielded a reproducibility of approximately 3.4 microm. CONCLUSIONS: Although ultrasound pachymeter measurements differed significantly from OLCR and OCP measurements, agreement was considered good because the mean differences were <10 microm, and the results can be regarded as clinically interchangeable.

Adult↗