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At least 649 records · Page 36Linked to original sources
PubMed2005

Superresolution imaging from limited-aperture optical diffracted field data.

The use of an optical waveguide to attain a numerical aperture of unity in computational coherent optical imaging applications is described. It is shown that for the case of a one-dimensional (slitlike) object radiating into an optical waveguide consisting of two plane-parallel mirrors the complex field amplitude across any cross section of the waveguide contains sufficient information to reconstruct the object's transmittance function with a numerical aperture of unity. We include the derivation of an inversion algorithm for performing the object reconstruction as well as computer simulations of the procedure.

Journal Article↗
PubMed2000

Imaging the optic nerve and ganglion cell layer.

New imaging techniques have extended the limitations of visualisation of the structures of the optic nerve and fundus in the living human eye. Quantitative reconstruction of depth of the optic nerve head is becoming widely available through the use of the confocal scanning laser ophthalmoscope (cSLO). A separate method of quantitative depth reconstruction is possible using stereo pairs which is not subject to the same artefacts as the tomographic reconstruction. We are investigating the use of these techniques both with conventional stereo imaging and using stereo pairs derived from cSLO images. In these we find that there is additional structural detail evident in the base of the optic nerve head. Further studies made with an instrument optimised to image this region show that this corresponds to the lamina cribrosa. Current work is aimed at further extending the limits of imaging using techniques based on optical coherence tomography, which provides additional depth resolution. Results to date with a prototype device show an improvement of approximately a factor of 10 in depth resolution and that some separate layers of the retina may be visualised including the photoreceptor layer. The goal is to extend these limits to allow visualisation of the ganglion cell layer.

Fovea Centralis↗
PubMedDate not supplied

Optical characterization of probes for photon scanning tunnelling microscopy.

The photon scanning tunnelling microscope is a well-established member of the family of scanning near-field optical microscopes used for optical imaging at the subwavelength scale. The quality of the probes, typically pointed uncoated optical fibres, used is however, difficult to evaluate in a direct manner and has most often been inferred from the apparent quality of recorded optical images. Complicated near-field optical imaging characteristics, together with the possibility of topographically induced artefacts, however, has increased demands for a more reliable probe characterization technique. Here we present experimental results obtained for optical characterization of two different probes by imaging of a well-specified near-field intensity distribution at various spatial frequencies. In particular, we observe that a sharply pointed dielectric probe can be highly suitable for imaging when using p-polarized light for the illumination. We conclude that the proposed scheme can be used directly for probe characterization and, subsequently, for determination of an optical transfer function. which would allow one to deduce from an experimentally obtained image of a weakly scattering sample the field distribution existing near the sample surface in the absence of the probe.

Journal Article↗
PubMed1995

Imaging of optic disc drusen: a comparative study.

The choice of imaging technique to identify the presence of optic disc drusen has not been well established. We performed computed tomography (CT), magnetic resonance imaging (MRI), fundus fluorescein angiography and B-mode ultrasonography (B-USG) on four patients with optic disc drusen as the sole identifiable pathological process. CT, MRI and examination for autofluorescence demonstrated the presence of drusen in only one case each. B-USG showed characteristic features of optic disc drusen in all cases. We suggest that B-USG, a non-invasive and inexpensive technique, may be the imaging method of choice in identifying the presence of disc drusen.

Fluorescein Angiography↗
PubMedDate not supplied

Quality analysis of in vivo near-infrared fluorescence and conventional gamma images acquired using a dual-labeled tumor-targeting probe.

The cyclic peptide, cyclopentapeptide cyclo(lys-Arg-Gly-Asp-phe) (c(KRGDf)), which is known to target alpha(v)beta3 integrin, is dual-labeled with a radiotracer, (111)indium, for gamma scintigraphy as well as with a near-infrared dye, IRDye800, for continuous-wave (cw) imaging of alpha(v)beta3 positive human M21 melanoma in xenografts. Twenty-four hours after administration of the dual-labeled peptide at a dose equivalent to 90 microCi of (111)In and 5 nmol of near-infrared (NIR) dye, whole-body gamma scintigraphy and cw imaging was conducted. Image acquisition time was 15 min for the gamma scintigraphy images and 800 ms for the optical images acquired using an NIR sensitive intensified charge-coupled device. The results show that while the target-to-background ratio (TBR) of nuclear and optical imaging were similar for surface regions of interest and consistent with the origin of gamma and NIR radiation from a common targeted peptide, the signal-to-noise ratio (SNR) was significantly higher for optical than nuclear imaging. Furthermore, an analysis of SNR versus contrast showed greater sensitivity of optical over nuclear imaging for the subcutaneous tumor targets. While tomographic reconstructions are necessary to probe TBR, SNR, and contrast for interior tissues, this work demonstrates for the first time the direct comparison of molecular optical and planar nuclear imaging for surface and subsurface cancers.

Animals↗
PubMedDate not supplied

Neuroimaging in epilepsy.

Neuroimaging techniques have improved the understanding, diagnosis, and management of epilepsy. By providing excellent structural information, MRI is the technique of choice in evaluating patients with epilepsy. Functional imaging techniques, including MR spectroscopy, functional MRI, positron emission tomography, and single photon emission CT, permit noninvasive assessment of the epileptic substrate, its functional status, and neuroreceptors. The MRI-based techniques will potentially assume a greater role in the cost-effective workup of the patient. Currently, newer techniques such as magnetoencephalography, magnetic source imaging, and optical imaging are research tools.

Brain↗
PubMed2000

New approaches for imaging in gene therapy.

Gene therapy is increasingly used experimentally and clinically to replace defective genes and/or impart new functions to cells and tissues. With the recent advances in vector design, improvements in transgene and prodrug activation strategies, gene therapy has been applied to a wide variety of diseases, tissues and organ systems. It is now clear that our specialty will play a critical role in gene therapy research and its clinical applications. Three aspects of gene therapy are of particular interest to imaging. The first is in delivering genes and vector products by minimally invasive interventional techniques. The second is in quantitating gene and DNA deliveries, for example, by nuclear imaging. Finally, imaging can be used to monitor the levels of transgene expression in vivo. A variety of imaging techniques including PET imaging, nuclear imaging, MR imaging and optical imaging can potentially be used to achieve the latter. This brief introductory overview is intended to summarize current strategies and illustrate the role that radiology will play in this field.

Animals↗
PubMed2004

Design and synthesis of a bimodal target-specific contrast agent for angiogenesis.

[structure: see text] A bimodal target-specific contrast agent based on a cyclic peptide containing the target-specific NGR sequence, gadolinium(III) diethylenetriaminepentaacetic acid (Gd(III)DTPA), and Oregon Green 488 (OG488) suitable for both MR imaging and optical imaging of angiogenesis is developed. The synthetic strategy for this target-specific contrast agent exploits the use of highly efficient, chemoselective reactions, such as native chemical ligation, and gives a straightforward approach for double labeling of peptides in general.

Carboxylic Acids↗
PubMed2003

Relation between cerebral blood flow and metabolism explained by a model of oxygen exchange.

The cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRo(2)) are major determinants of the contrast in functional magnetic resonance imaging and optical imaging. However, the coupling between CBF and CMRo(2) during cerebral activation remains controversial. Whereas most of the previous models tend to show a nonlinear coupling, experimental studies have led to conflicting conclusions. A physiologic model was developed of oxygen transport through the blood-brain barrier (BBB) for dynamic and stationary states. Common model simplifications are proposed and their implications for the CBF/CMRo(2) relation are studied. The tissue oxygen pool, the BBB permeability, and the hemoglobin dissociation curve are physiologic parameters directly involved in the CBF/CMRo(2) relation. We have been shown that the hypothesis of a negligible tissue oxygen pool, which was admitted by most of the previous models, implies a tight coupling between CBF and CMRo(2). By relaxing this hypothesis, a real uncoupling was allowed that gives a more coherent view of the CBF/CMRo(2) relation, in better agreement with the hypercapnia data and with the variability reported in experimental works for the relative changes of those two variables. This also allows a temporal mismatch between CBF and CMRo(2), which influences the temporal shape of oxygenation at the capillary end.

Brain↗
PubMed1997

Delayed signal propagation via CA2 in rat hippocampal slices revealed by optical recording.

Signal propagation from mossy fibers to CA1 neurons was investigated in rat hippocampal slices by a combination of electrical and optical recordings. The slices were prepared by oblique sectioning of the middle part of the hippocampus to preserve fiber connections. The mossy fibers were stimulated to induce population spikes (PSs) and excitatory postsynaptic potentials in the middle part of the CA1 region. Latencies of maximal PSs in CA1 varied widely among slices; they ranged from 7 to 13.5 ms, with two maxima at 9 and 11.5 ms. The fastest PSs probably are evoked by the Schaffer collaterals that connect the CA3 and CA1 regions in the well-known trisynaptic circuit. However, the slower PSs suggest the existence of additional delayed inputs. To determine the source of the delayed input, slices were stained with a voltage-sensitive dye, RH482, and the optical signals relevant to membrane potential changes were detected by a high-resolution optical imaging system. Optical recording of responses to mossy fiber stimulation indicated two distinct types of signal propagation from CA3 to CA1. In preparations evincing the fast type of propagation, signals spread to CA1 within 7.2 ms after the mossy fiber stimulation. During such propagation, activity flowed directly from CA3 to the stratum radiatum of CA1. Other preparations illustrated slow signal propagation, in which optical signals were generated in CA2 before spreading to CA1. During such slow signal transmission, activity persisted in CA2 and its surrounding area for 3 ms before propagating to the strata radiatum and oriens in CA1. In such cases, CA1 activity was detected within 10.8 ms of mossy fiber stimulation. In some slices, a mixture of the fast and slow propagation patterns was observed, indicating that these two transmission modes can coexist. Our data reveal that CA2 neurons can transmit delayed excitatory signals to CA1 neurons. We therefore conclude that consideration of electrical signal propagation through the hippocampus should include flow through the CA2 region in addition to the traditional dentate gyrus-CA3-CA1 trisynaptic circuit.

Animals↗
PubMed2005

Component spatial pattern analysis of chemicals by use of two-dimensional electro-optic terahertz imaging.

We demonstrate a method of chemical mapping by using the transillumination terahertz (THz) images obtained by two-dimensional electro-optic THz imaging. The images and spectral data were measured between 0.1 and 1.0 THz. An experimental sample consisting of three chemicals was prepared, with one in two concentrations. By introducing the component spatial pattern analysis based on the least-squares method, the chemical composition, spatial distribution, and difference in concentration were clearly determined.

Journal Article↗
PubMed2000

Active constrained truncated Newton method for simple-bound optical tomography

In the past, nonlinear unconstrained optimization of the optical imaging problem has focused on Newton-Raphson techniques. Besides requiring expensive computation of the Jacobian, the unconstrained minimization with Tikhonov regularization can pose significant storage problems for large-scale reconstructions, involving a large number of unknowns necessary for realization of optical imaging. We formulate the inverse optical imaging problem as both simple-bound constrained and unconstrained minimization problems in order to illustrate the reduction in computational time and storage associated with constrained image reconstructions. The forward simulator of excitation and generated fluorescence, consisting of the Galerkin finite-element formulation, is used in an inverse algorithm to find the spatial distribution of absorption and lifetime that minimizes the difference between predicted and synthetic frequency-domain measurements. The inverse approach employs the truncated Newton method with trust region and a modification of automatic reverse differentiation to speed the computation of the optimization problem. The reconstruction results confirm that the physically based, constrained minimization with efficient optimization schemes may offer a more logical approach to the large-scale optical imaging problem than unconstrained minimization with regularization.

Journal Article↗
PubMed2002

Estimation of longitudinal resolution in optical coherence imaging.

The spectral shape of a source is of prime importance in optical coherence imaging because it determines several aspects of image quality, especially longitudinal resolution. Wide spectral bandwidth, which provides short coherence length, is sought to obtain high-resolution imaging. To estimate longitudinal resolution, the spectral shape of a source is usually assumed to be Gaussian, although the spectra of real sources are typically non-Gaussian. We discuss the limit of this assumption regarding the estimation of longitudinal resolution. To this end, we also investigate how coherence length is related to longitudinal resolution through the evaluation of different definitions of the coherence length. To demonstrate our purpose, the coherence length for several theoretical and real spectral shapes of sources having the same spectral bandwidth and central wavelength is computed. The reliability of coherence length computations toward the estimation of longitudinal resolution is discussed.

Journal Article↗
PubMedDate not supplied

Clinical application of a magneto-optical disk image filing system/image save and carry (ISAC) system.

We propose the utilization of portable magneto optical disks for image filing. The main problems in PACS are the need for a high-speed local area network (LAN) and a large mass storage device. An image filing system--image save and carry (ISAC)--is one solution for these problems in present PACS and requires minimal additional hardware and cost for the installation. Whenever a patient is examined, the clerk carries the medical record and the ISAC magneto-optical disk for recording image data, and after inspection records the image data into the magneto-optical disk. We investigated the number of image retrievals done for inpatients and outpatients in 1988 at our radiation therapy department. The data storage requirements were on the average 18.5 MB for outpatients and 173.9 MB for inpatients. An ISAC display console needs also an easy-to-use man/machine interface for specifying images and image display characteristics in order to realize the ISAC system.

Computer Systems↗
PubMed2005

Compartment-resolved imaging of activity-dependent dynamics of cortical blood volume and oximetry.

Optical imaging, positron emission tomography, and functional magnetic resonance imaging (fMRI) all rely on vascular responses to image neuronal activity. Although these imaging techniques are used successfully for functional brain mapping, the detailed spatiotemporal dynamics of hemodynamic events in the various microvascular compartments have remained unknown. Here we used high-resolution optical imaging in area 18 of anesthetized cats to selectively explore sensory-evoked cerebral blood-volume (CBV) changes in the various cortical microvascular compartments. To avoid the confounding effects of hematocrit and oximetry changes, we developed and used a new fluorescent blood plasma tracer and combined these measurements with optical imaging of intrinsic signals at a near-isosbestic wavelength for hemoglobin (565 nm). The vascular response began at the arteriolar level, rapidly spreading toward capillaries and venules. Larger veins lagged behind. Capillaries exhibited clear blood-volume changes. Arterioles and arteries had the largest response, whereas the venous response was smallest. Information about compartment-specific oxygen tension dynamics was obtained in imaging sessions using 605 nm illumination, a wavelength known to reflect primarily oximetric changes, thus being more directly related to electrical activity than CBV changes. Those images were radically different: the response began at the parenchyma level, followed only later by the other microvascular compartments. These results have implications for the modeling of fMRI responses (e.g., the balloon model). Furthermore, functional maps obtained by imaging the capillary CBV response were similar but not identical to those obtained using the early oximetric signal, suggesting the presence of different regulatory mechanisms underlying these two hemodynamic processes.

Animals↗
PubMed1977

Real-space filtering of electron images from optical autocorrelation patterns.

The capability for filtering electron images, in real space, is demonstrated to be inherent to a two plate, incoherent optical procedure (originally described by Meyer-Eppler and Darius) for recording autocorrelation functions from transparencies. If an image contains features that occur with more than random frequency, these features may give rise to a resolvable peak in the optically recorded autocorrelation function. The optical requirements for obtaining an image of the transparency that is filtered to observe only features giving rise to some set of such peaks, or to exclude them, are described. The principle is to form an image of the transparency, with a properly placed plano-convex lens, from the incoherent light transmitted through apertures positioned over the peaks in the autocorrelation plane. The application of the method in defining the position and orientation of specific projections of protein molecules, as observed in negative stain by bright-field, or unstained by dark-field electron microscopy, is also described.

Animals↗
PubMed2003

Near-field optics: from subwavelength illumination to nanometric shadowing.

Near-field optics uniquely addresses problems of x, y and z resolution by spatially confining the effect of a light source to nanometric domains. The problems in using far-field optics (conventional optical imaging through a lens) to achieve nanometric spatial resolution are formidable. Near-field optics serves a bridging role in biology between optical imaging and scanned probe microscopy. The integration of near-field and scanned probe imaging with far-field optics thus holds promise for solving the so-called inverse problem of optical imaging.

Delivery of Health Care, Integrated↗
PubMed2004

Fusion of computed tomography data and optical 3D images of the dentition for streak artefact correction in the simulation of orthognathic surgery.

OBJECTIVE: To determine the limits of accuracy of fusion of optical three-dimensional (3D) imaging and computed tomography (CT) with and without metal artefacts in an experimental setting and to show the application of this hybrid system in 3D orthognathic surgery simulation. METHODS: Ten plaster casts of dental arches were subjected to a CT scan and optical 3D surface imaging. Subsequently, the first molars in the plaster casts were supplied with metal restorations, bilaterally, and new CT scans and optical surface images were assessed. The registration of the surface data of the two imaging modalities of the study models without and with metal restorations was carried out. The mean distance between the two data sets was calculated. From a patient a CT scan of the skull as well as optical 3D images of plaster casts of the dental arches were acquired. Again the two imaging modalities were registered and virtual orthognathic surgery simulation was carried out. RESULTS: The mean distance between the corresponding data points of CT and optical 3D surface images was 0.1262+/-0.0301 mm and 0.2671+/-0.0580 mm, respectively, for the plaster casts without and with metal restorations. The differences between these data were statistically significant (P<0.0005). For the patient case a mean difference of 0.66+/-0.49 mm and 0.56+/-0.48 mm for mandible and maxilla, respectively, was calculated between CT and optical surface data. CONCLUSION: The accuracy of the fusion of 3D CT surface data and optical 3D imaging is significantly reduced by metal artefacts. However, it seems appropriate for virtual orthognathic surgery simulation, as post-operative orthodontics are performed frequently.

Adult↗