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Results for “Optical imaging”

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At least 955 records · Page 53Linked to original sources
PubMed2003

Characterization and fabrication of fully metal-coated scanning near-field optical microscopy SiO2 tips.

The fabrication of silicon cantilever-based scanning near-field optical microscope probes with fully aluminium-coated quartz tips was optimized to increase production yield. Different cantilever designs for dynamic- and contact-mode force feedback were implemented. Light transmission through the tips was investigated experimentally in terms of the metal coating and the tip cone-angle. We found that transmittance varies with the skin depth of the metal coating and is inverse to the cone angle, meaning that slender tips showed higher transmission. Near-field optical images of individual fluorescing molecules showed a resolution < 100 nm. Scanning electron microscopy images of tips before and after scanning near-field optical microscope imaging, and transmission electron microscopy analysis of tips before and after illumination, together with measurements performed with a miniaturized thermocouple showed no evidence of mechanical defect or orifice formation by thermal effects.

Aluminum↗
PubMed2004

Optical section retinal imaging and wavefront sensing in diabetes.

PURPOSE: To investigate differences in higher-order ocular aberrations and in optical section retinal image resolution between healthy normal and diabetic subjects. METHODS: An optical imaging system was established for combined retinal optical section imaging and wavefront sensing. A laser beam was expanded and focused to a point on the retina by the optics of the eye. For optical section retinal imaging, a cylindrical lens was placed in the path of the incident laser beam to form a focused line on the retina. Because of the angle between the incident laser and imaging path, an optical section image of the retina was captured. For wavefront sensing, a Shack-Hartmann aberrometer was incorporated in the imaging system. Twenty-two subjects with diabetes (average age, 52 +/- 12 years) and 13 normal subjects (average age, 47 +/- 9 years) were imaged. Retinal depth resolution was determined from the width of the laser line on the retina. Higher-order ocular aberrations were determined from the root mean square of the third to seventh Zernike terms, characterizing the wavefront aberration function. The data were analyzed statistically using Student's t-test and linear regression. RESULTS: Higher-order ocular aberrations in diabetic subjects were significantly higher than in normal subjects (p=0.03). The retinal image depth resolution in diabetic subjects was significantly lower than in normal subjects (p <0.001). The retinal image depth resolution was inversely correlated with higher-order aberrations (r=-0.5; p=0.007; N=35). CONCLUSIONS: The results demonstrate disease-related increases in higher-order ocular aberrations that influence retinal image resolution in diabetic eyes. This information is useful for designing high-resolution retinal imaging systems applicable for eyes with retinal disease.

Adult↗
PubMed2003

Three-dimensional point spread functions of an optical heterodyne scanning image processor.

We study the three-dimensional (3-D) imaging properties of an optical heterodyne scanning image processor. The image processor is a two-pupil optical system capable of 3-D imaging coherently or incoherently, depending on the detection scheme used. We derive the imaging properties in terms of the two pupils and then show an important 3-D imaging application in scanning holography by deriving its 3-D point spread functions and compare them with conventional 3-D imaging systems.

Journal Article↗
PubMed2004

Automated hybrid TACT volume reconstructions.

OBJECTIVES: To design, implement in Java, and evaluate a method and means for the automated localization of artificial landmarks in optical images for tuned-aperture computed tomography (TACT) that allows the replacement of radiographic with optical landmarks. METHODS: Circular, colored, optical landmarks were designed to provide flexibility with regard to landmark constellation, imaging equipment, and lighting conditions. The landmark detection was based on Hough transforms (HT) for ellipses and lines. The HT for ellipses was extended to enable selective detection of bright ellipses on a dark background and vice versa, and the number of irrelevant votes in the accumulator arrays was reduced. An experiment was performed in vitro to test the automated landmark localization scheme, verify registration accuracy, and measure the required computation time. RESULTS: A visual evaluation of the tomographic slices that were produced using the new method revealed good registration accuracy. A comparison to tomographic slices similarly produced by means of conventional TACT showed identical results. The algorithm ran sufficiently fast on standard hardware to allow landmark localization in "real time" during successive image acquisition in clinical applications. CONCLUSIONS: The proposed method provides robust automated localization of landmarks in optical images. Using a hybrid imaging system, TACT can now be clinically applied without manual interaction of a human operator and without radiopaque landmarks, which might cover anatomic details of diagnostic interest.

Algorithms↗
PubMed2004

Image analysis of optic nerve disease.

Existing methodologies for imaging the optic nerve head surface topography and measuring the retinal nerve fibre layer thickness include confocal scanning laser ophthalmoscopy (Heidelberg retinal tomograph), optical coherence tomography, and scanning laser polarimetry. For cross-sectional screening of patient populations, all three approaches have achieved sensitivities and specificities within the 60-80th percentile in various studies, with occasional specificities greater than 90% in select populations. Nevertheless, these methods are not likely to provide useful assistance for the experienced examiner at their present level of performance. For longitudinal change detection in individual patients, strategies for clinically specific change detection have been rigorously evaluated for confocal scanning laser tomography only. While these initial studies are encouraging, applying these algorithms in larger numbers of patients is now necessary. Future directions for these technologies are likely to include ultra-high resolution optical coherence tomography, the use of neural network/machine learning classifiers to improve clinical decision-making, and the ability to evaluate the susceptibility of individual optic nerve heads to potential damage from a given level of intraocular pressure or systemic blood pressure.

Diagnostic Imaging↗
PubMed2004

Sagittal laser optical tomography for imaging of rheumatoid finger joints.

We present a novel optical tomographic imaging system that was designed to determine two-dimensional spatial distribution of optical properties in a sagittal plane through finger joints. The system incorporates a single laser diode and a single silicon photodetector into a scanning device that records spatially resolved light intensities as they are transmitted through a finger. These data are input to a model-based iterative image reconstruction (MOBIIR) scheme, which uses the equation of radiative transfer (ERT) as a forward model for light propagation through tissue. We have used this system to obtain tomographic images of six proximal interphalangeal finger joints from two patients with rheumatoid arthritis. The optical images were compared to clinical symptoms and ultrasound images.

Algorithms↗
PubMed1996

Prognostic value of magnetic resonance imaging in monosymptomatic optic neuritis.

PURPOSE: Magnetic resonance imaging is able to depict lesions in the optic nerve in the acute stage of monosymptomatic optic neuritis. Most patients have lesions located intraorbitally, intracanalicularly, and/or intracranially. The goal of this study is to determine whether these lesions resolve after visual recovery, change in length or localization, or could be correlated to the visual function. METHODS: Between 1987 and 1992, the authors examined 22 patients with acute optic neuritis using magnetic resonance imaging short-time inversion recovery sequences. Additionally, the authors determined visual acuity, visual field, color vision, contrast sensitivity, and visual-evoked responses. All patients were re-examined between 1993 and 1994 in the same manner. Visual recovery in the re-examination was divided into three groups: group 1 with complete visual recovery (visual acuity better than 20/25); group 2 with incomplete recovery (visual acuity better than 20/25 but defect in at least one of the other tests: visual field, color vision, and contrast sensitivity); and group 3 with partial recovery (visual acuity remained less than 20/25, defect in all the other tests). RESULTS: All group 1 patients initially had lesions less than 17.5 mm, group 2 patients had lesions greater than 17.5 mm (44%) and/or lesions located intracanalicularly (66%), and most of group 3 patients initially had lesions greater than 17.5 mm (79%). CONCLUSION: Eyes with lesions less than 17.5 mm in the optic nerve in acute optic neuritis have a good prognosis for visual recovery. Lesions greater than 17.5 mm or lesions involving the intracanalicular portion of the optic nerve lead to incomplete or partial visual recovery.

Acute Disease↗
PubMed2004

Phase plate to extend the depth of field of incoherent hybrid imaging systems.

A hybrid imaging system combines a modified optical imaging system and a digital postprocessing step. We describe a spatial-domain method for designing a pupil phase plate to extend the depth of field of an incoherent hybrid imaging system with a rectangular aperture. We use this method to obtain a pupil phase plate to extend the depth of field, which we refer to as a logarithmic phase plate. Introducing a logarithmic phase plate at the exit pupil of a simulated diffraction-limited system and digitally processing the detector's output extend the depth of field by an order of magnitude more than the Hopkins defocus criterion. We also examine the effect of using a charge-coupled device optical detector, instead of an ideal optical detector, on the extension of the depth of field. Finally, we compare the performance of the logarithmic phase plate with that of a cubic phase plate in extending the depth of field of a hybrid imaging system with a rectangular aperture.

Journal Article↗
PubMed2005

Gold nanoshell bioconjugates for molecular imaging in living cells.

Advances in scattering-based optical imaging technologies offer a new approach to noninvasive point-of-care detection, diagnosis, and monitoring of cancer. Emerging photonics technologies provide a cost-effective means to image tissue in vivo with high resolution in real time. Advancing the clinical potential of these imaging strategies requires the development of optical contrast agents targeted to specific molecular signatures of disease. We describe the use of a novel class of contrast agents based on nanoshell bioconjugates for molecular imaging in living cells. Nanoshells offer significant advantages over conventional imaging probes including continuous and broad wavelength tunability, far greater scattering and absorption coefficients, increased chemical stability, and improved biocompatibility. We show that nanoshell bioconjugates can be used to effectively target and image human epidermal growth factor receptor 2 (HER2), a clinically relevant biomarker, in live human breast carcinoma cells.

Breast Neoplasms↗
PubMed2004

Imaging single cardiac ryanodine receptor Ca2+ fluxes in lipid bilayers.

In this and an accompanying report we describe two steps, single-channel imaging and channel immobilization, necessary for using optical imaging to analyze the function of ryanodine receptor (RyR) channels reconstituted in lipid bilayers. An optical bilayer system capable of laser scanning confocal imaging of fluo-3 fluorescence due to Ca2+ flux through single RyR2 channels and simultaneous recording of single channel currents was developed. A voltage command protocol was devised in which the amplitude, time course, shape, and hence the quantity of Ca2+ flux through a single RyR2 channel is controlled solely by the voltage imposed across the bilayer. Using this system, the voltage command protocol, and concentrations of Ca2+ (25-50 mM) that result in saturating RyR2 Ca2+ currents, proportional fluo-3 fluorescence was recorded simultaneously with Ca2+ currents having amplitudes of 0.25-14 pA. Ca2+ sparks, similar to those obtained with conventional microscope-based laser scanning confocal systems, were imaged in mouse ventricular cardiomyocytes using the optical bilayer system. The utility of the optical bilayer for systematic investigation of how cellular factors extrinsic to the RyR2 channel, such as Ca2+ buffers and diffusion, alter fluo-3 fluorescent responses to RyR2 Ca2+ currents, and for addressing other current research questions is discussed.

Animals↗
PubMed2002

Reduced depth of field in incoherent hybrid imaging systems.

A hybrid imaging system combines a modified optical imaging module and a digital postprocessing step. We define what to our knowledge is a new metric to quantify the blurring of a defocused image that is more suitable than the defocus parameter for describing defocused hybrid imaging systems. We use this metric to design a pupil phase grating to reduce the depth of field, thereby increasing the axial resolution, of an incoherent hybrid imaging system using quasi-monochromatic illumination. By introducing this grating at the exit pupil and digitally processing the output of the detector, we reduce the depth of field by more than a factor of 2. Finally, we examine the effect of using a CCD optical detector, instead of an ideal optical detector, on the reduction of the depth of field.

Journal Article↗
PubMed2006

Studies of plasma membrane mechanics and plasma membrane-cytoskeleton interactions using optical tweezers and fluorescence imaging.

We use optical tweezers in conjunction with an optical position-sensing system, which spectrally filters signals generated by a trapped fluorescent microsphere to study plasma membrane (PM) mechanics and its interactions with cytoskeleton. We dynamically measure the PM tethering force on human embryonic kidney cells that are a standard cultured cell line. Recorded tethering force vs. PM displacement profiles, revealed the tether formation process, initiated with linear deformation of the PM, followed by a nonlinear regime and terminated with the local separation of PM. Tethering force vs. displacement profiles were used to estimate tether formation force and stiffness parameter of the PM. Integration of the force-displacement profiles yielded the work of tether formation, including linear and nonlinear components. Our results demonstrate that spectral filtering of the optically trapped fluorescent microsphere image formed on the position-sensing system overcomes the artifacts introduced by the transillumination imaging and allows accurate measures of PM mechanics before and during the initial stages of tether formation.

Biomechanical Phenomena↗
PubMed2006

Characterization of physical properties of supported phospholipid membranes using imaging ellipsometry at optical wavelengths.

Subnanometer-scale vertical z-resolution coupled with large lateral area imaging, label-free, noncontact, and in situ advantages make the technique of optical imaging ellipsometry (IE) highly suitable for quantitative characterization of lipid bilayers supported on oxide substrates and submerged in aqueous phases. This article demonstrates the versatility of IE in quantitative characterization of structural and functional properties of supported phospholipid membranes using previously well-characterized examples. These include 1), a single-step determination of bilayer thickness to 0.2 nm accuracy and large-area lateral uniformity using photochemically patterned single 1,2-dimyristoyl-sn-glycero-3-phosphocholine bilayers; 2), hydration-induced spreading kinetics of single-fluid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayers to illustrate the in situ capability and image acquisition speed; 3), a large-area morphological characterization of phase-separating binary mixtures of 1,2-dilauroyl-sn-glycero-3-phosphocholine and galactosylceramide; and 4), binding of cholera-toxin B subunits to GM1-incorporating bilayers. Additional insights derived from these ellipsometric measurements are also discussed for each of these applications. Agreement with previous studies confirms that IE provides a simple and convenient tool for a routine, quantitative characterization of these membrane properties. Our results also suggest that IE complements more widely used fluorescence and scanning probe microscopies by combining large-area measurements with high vertical resolution without the use of labeled lipids.

Cholera Toxin↗
PubMed2000

Cortical imaging: capturing the moment.

Recent advances in optical imaging techniques using voltage-sensitive dyes have provided new insights into the dynamic of neural processing in distributed cortical networks.

Action Potentials↗
PubMed1998

Imaging techniques in microbiology.

Recent advances in optical imaging have dramatically expanded the capabilities of the light microscope and its usefulness in microbiology research. Some of these advances include improved fluorescent probes, better cameras, new techniques such as confocal and deconvolution microscopy, and the use of computers in imaging and image analysis. These new technologies have now been applied to microbiological problems with resounding success.

Cell Compartmentation↗
PubMed2004

[Oriented immobilization of human IgG by protein A on imaging ellipsometry biosensor].

The biosensor based on optical imaging ellipsometry, can be used to detect directly, without labeling, the surface concentration of biomolecules on solid surface. The feasibility of using protein A to immobilize antibody on the silicon surface of the imaging ellipsometry biosensor was investigated in this study. The results showed that the anti-IgG immobilized by the protein A on silicon surface could bind effectively human IgG, and the human IgG immobilized on silicon surface by protein A bound more polyclonal antibody molecules than that immobilized on silicon surface directly, suggesting that protein A might block the surface to prevent the absorption of human IgG on surface directly, which might compromise its native configuration. The silicon surface modified with protein A is expected to be used to immobilize a variety of antibodies, as protein A can bind selectively the Fc regions of many mammalian IgG. The combination of imaging ellipsometry and the protein A surface modification has the potential to be developed into immunoassays of high sensitivity.

Biosensing Techniques↗
PubMedDate not supplied

An artificial compound eye for stereoendoscopy.

A scanning endoscope has been designed with the ability to both project three-dimensional images and provide precise measurements of internal structures. This is beneficial for minimally invasive surgery, where surgeons suffer from a lack of depth perception, limited field of view, and the absence of a reference frame for dimensional measurements. Borrowing from the insect compound eye, the design uses an array of prisms, each facing a different direction but with overlapping fields of view. The prisms redirect their respective images normal to a fibre optic imaging plane and are individually controlled by electro-chromic shutters. The device thereby retains the ability to scan in multiple directions without mechanical parts and uses only a single camera. Comparison of the overlapping images with known prism positions allows for the calculation of absolute coordinates. Results from large-scale models show that the technology is plausible, and fabrication methods for a smaller device are discussed.

Depth Perception↗
PubMed1994

Resolution of annular-pupil optical systems.

The resolution of optical systems with annular pupil objectives is discussed, particularly with respect to the imaging properties of soft-x-ray imaging optical systems. Images of two dark bars in a bright field and knife-edge responses, which are calculated with partially coherent transfer functions, were used to estimate the resolution. Resolution for two bright points in a dark field, which is conventionally used in Rayleigh's analysis, is also discussed for comparison. It was found that annular systems with obstruction ratios of more than 0.6 show resolution properties different from those of systems with low-obstruction-ratios. The high-obstruction-ratio systems show lower resolution for the two-dark-bar objects and higher resolution for the two-bright-point objects, whereas the low-obstruction-ratio system show almost the same resolution for both objects.

Light↗