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At least 397 records · Page 22Linked to original sources
PubMed2004

Observation of polarization property in near-field optical imaging by a polarization-maintaining fiber probe.

We fabricated an original near-field scanning optical microscopy (NSOM) fiber probe made of polarization-maintaining and attenuation-reducing (PANDA)-type polarization-maintaining optical fiber, and observed the polarization property of propagation light in a polymer optical waveguide. The distribution of the transmission coefficient in polarization angles through this NSOM probe showed that the linear polarization is maintained in the two crossing directions: the fast and slow axes. The polarization degree parallel to the slow axis decreases from 1000:1 to 2:1 by bending the fiber probe and the decrease is independent of the bending direction. Using this PANDA-type NSOM probe, we investigated the polarization property of periodic intensity modulation. It was found that the intensity modulation was observed clearly with the electric vector parallel to the radius direction of the waveguide, but was observed vaguely with the electric vector perpendicular to the radius direction.

Journal Article↗
PubMed1996

Optical imaging of the ventral medullary surface of developing kittens during ventilatory challenges.

We used large-array optical recording procedures to examine maturation of regional neural activity within the ventral medullary surface (VMS) of anaesthetized kittens during graded hypercapnic and hypoxic challenges. The VMS was exposed through a ventral surgical approach in 10, 20, 30, and 45-day-old kittens and in adult cats under sodium pentobarbital anaesthesia. Arterial pressure, costal diaphragmatic EMG, and ECG were continuously monitored. A coherent image conduit with 12 mu fibre resolution was attached to a charge-coupled-device camera and positioned over the VMS. Reflected 660 nm light was digitized continuously at 2-s intervals during a baseline period, hyperoxic hypercapnia, (3, 5, and 10% CO2 in O2), and poikylocapnic hypoxia (6%, 9%, and 12% O2 in N2), and recovery. Sixty to seventy-five images within each epoch were averaged, and subtracted from baseline. Regional differences within the image were determined by ANOVA procedures (alpha = 0.05). During hypercapnia, an overall decrease in neural activity (increase in scattered light) occurred, which was marginally age-dependent. By 30 days, regional bidirectional reflectance changes in response to CO2 emerged in a small proportion of animals, and were similar to adult responses. Hypoxia induced a dose- and age-dependent decrease in overall scattered light. Transient "on" and "off" responses were common under both ventilatory stimuli. In 20-30-day kittens, marked rebound responses in reflectance accompanied cessation of hypoxic stimuli; such patterns were absent at other ages. At 30 days, a caudal-rostral bidirectionality in response to mild hypoxia (12% O2) began to emerge in a subset of animals. We conclude that dose-dependent response to ventilatory stimuli occur in the VMS at all post-natal ages of the kitten; however, in hypoxia, the magnitude of the overall reflectance changes is diminished relative to adult patterns. Rebound responses to hypoxia are present at particular ages, and older kittens begin to show a topographical organization of neural activation.

Analysis of Variance↗
PubMed1993

Optical imaging of shock waves produced by a high-energy electromagnetic transducer.

An electromagnetic acoustic transducer (EMAT) and acoustic lens have been constructed to provide reproducible and well characterized acoustic shock waves in water. The peak pressure amplitude variation for the unfocused and focused shock waves was found to be within +/- 5%. The focal region has been characterized both optically and by conventional piezoelectric pressure measurements. Optical investigations centre around ruby laser illuminated Schlieren and focused shadow imaging. The temporal resolution of the optical technique was determined by the ruby laser pulse length of 20 ns, giving a spatial resolution of 30 microns for a shock front in water.

Acoustics↗
PubMed1999

Optical imaging of the spatiotemporal patterning of neural responses in the embryonic chick superior cervical ganglion.

Multiple-site optical recording of transmembrane potential changes with a voltage-sensitive dye was used to reveal the functional expression and developmental changes of the postsynaptic potentials in the early embryonic chick superior cervical ganglion. The ganglia were isolated from five- to 12-day-old chick embryos with preganglionic nerve fibres (vertebral and/or cervical carotic nerves) attached. The preparations were stained with a voltage-sensitive merocyanine-rhodanine dye (NK2761). Voltage-related optical (absorbance) changes were recorded simultaneously from 127 contiguous loci in the preparation, using a 12 x 12-element photodiode array. Optical changes having two components were evoked by preganglionic nerve stimulation. One component was the fast spike-like signal and another the delayed slow signal. The amplitude of the slow signal was decreased by repetitive stimulation, reduced by low external calcium ion concentrations and eliminated in the presence of manganese or cadmium ions. The slow signals were also eliminated in the presence of D-tubocurarine. Accordingly, we concluded that the slow signal corresponds to cholinergic excitatory postsynaptic potentials. In the five- and six-day-old superior cervical ganglia, only the fast optical signals (referred to as the action potentials) were recorded. Slow optical signals (referred to as the excitatory postsynaptic potentials) were detected from preparations older than seven days. The amplitude of the slow optical signal gradually increased, together with an expansion of the response area, as the developmental stage proceeded from seven to 10 days. To compare the distribution patterns of the neural responses evoked by stimuli applied to the cervical carotic and vertebral nerves, we have mapped and imaged the spatial patterning of the synaptic responses. In the maps, the positions of the peak size regions of the slow signals were assessed, and we found that there were differences in the location of these areas for the cervical carotic vs vertebral nerves. From these experimental results, we conclude that synaptic function within the chick superior cervical ganglion is initiated at the seven-day-old embryonic stage, and reaches a maximum level at 10 days. Synaptic transmission at these stages is mediated solely by nicotinic acetylcholine receptors. The spatial mapping of the synaptic responses reveals that the neural populations related synaptically to the cervical carotic and vertebral nerves are located separately within the ganglion, even at an early developmental stage.

Animals↗
PubMed1993

Optical imaging of the ventral medullary surface of cats: hypoxia-induced differences in neural activation.

Large-array optical recording procedures provide the potential to examine simultaneous activity of large numbers of neurons. We applied this technique to examine regional neuronal activation on the ventral medullary surface (VMS) of cats during hypoxic challenges. VMS was exposed through a ventral surgical approach in eight adult cats under pentobarbital sodium anesthesia. Arterial pressure, end-tidal CO2, costal diaphragmatic electromyograms, and electrocardiograms were continuously monitored. A coherent image conduit with 12-microns-fiber resolution was attached to a charge-coupled device camera and positioned over the VMS. Reflected 700-nm light was digitized continuously at 2- to 3-s intervals during baseline period, hypoxic (6, 9, and 12% O2 in N2) exposure, and recovery. Forty images within each epoch were averaged and subtracted from baseline. Regional differences within the image were determined by analysis of variance procedures (alpha = 0.05). In caudal VMS, hypoxic challenges with 12% O2 consistently induced a regional diminution in reflected light (increased neural activity) that was rapid in onset and persisted for approximately 20 min after termination of exposure, well beyond the duration of discernible ventilatory alterations. In contrast, the same challenge resulted in decreased neural activity of similar duration in rostral VMS areas. Challenges with lower inspired concentrations of O2 reversed the pattern of diminished neural activity in rostral regions and led to a dose-dependent increase in neural activity, a dependency also observed in caudal VMS. We conclude that caudal VMS neurons demonstrate a unidirectional dose-dependent response pattern to hypoxic stimuli, whereas rostral VMS regions exhibit a bidirectional response to increasing hypoxic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2002

Optical imaging of PKH-labeled hematopoietic cells in recipient bone marrow in vivo.

This work describes an optical technique for characterization of the early stages of hematopoietic stem cell (HSC) engraftment under physiological conditions and in real time. Bone marrow cells (BMCs) labeled with PKH membrane linkers were injected into conditioned recipients (B10-->B10.BR mice) preoperated for placement of optical windows over femoral epiphyses. Labeled cells were tracked in vivo by fluorescence microscopy. Cellular adhesion to the BM stroma was tested with laser tweezers, and viability was assayed by the propidium iodide (PI) exclusion test, as determined from energy-transfer measurements of the pair PKH67-PI in freshly excised femurs in situ. At optimal concentrations for in vivo tracking, 1-4 micro M PKH dyes neither impaired the viability of BMCs nor the capacity of allogeneic HSCs to reconstitute hematopoiesis in myeloablated recipients. The optical window allowed in vivo visualization of 23%-26% of the PKH-labeled BMCs in the femur. The homing efficiencies at 16 hours posttransplantation were quantified as 1.77% +/- 0.15% and 0.21% +/- 0.02% for syngeneic and allogeneic BMCs, respectively. In femurs excised 16 hours after transplantation, 70% +/- 9% of the cells were adherent to the BM stroma, and two-thirds of the cells were PI negative (viable). In vivo tracking and in situ assessment of labeled HSCs in recipient BM provide important quantitative and qualitative insights into the early stages of engraftment. Correlation of early events and the efficiency of durable engraftment serve as the basis for a systematic approach toward optimization of the conditions for transplantation.

Animals↗
PubMed2003

Near-infrared optical imaging of epidermal growth factor receptor in breast cancer xenografts.

The specificity of a novel epidermal growth factor (EGF)-Cy5.5 fluorescent optical probe in the detection of EGF receptor (EGFr) was assessed using continuous-wave fluorescence imaging accomplished via an intensified charge-coupled device (CCD) camera. Human mammary MDA-MB-468 (EGFr+) and MDA-MB-435 (EGFr-) cancer cells were incubated with Cy5.5, EGF-Cy5.5, or the anti-EGFr monoclonal antibody C225 or EGF followed by EGF-Cy5.5 and examined under a fluorescence microscope. In vivo imaging was performed on mice with s.c. MDA-MB-468 and MDA-MB-435 tumors. Images were obtained every 6 s for 20 min after i.v. injection of each agent and every 24 h after injection for up to 192 h. Additionally, mice with MDA-MB-468 tumors were injected i.v. with C225 24 h before injection of EGF-Cy5.5. EGF-Cy5.5, but not Cy5.5 or indocyanine green dye (ICG), bound to MDA-MB-468 cells. Binding of EGF-Cy5.5 was blocked by C225 and by EGF. In contrast, binding of EGF-Cy5.5 to MDA-MB-435 cells was not observed. Monitoring of the time-fluorescence intensity in mice confirmed that ICG and Cy5.5 had no favorable binding to tumor regardless of EGFr expression level. In contrast, EGF-Cy5.5 accumulated only in MDA-MB-468 tumors. Moreover, tumor uptake of EGF-Cy5.5 was blocked by C225. ICG and Cy5.5 fluorescence was completely absent from the tumor site, regardless of EGFr expression level, 24 h after injection. Little EGF-Cy5.5 fluorescence was detected in MDA-MB-435 tumors 24 h after injection. In MDA-MB-468 tumors, our data suggest that EGF-Cy5.5 may be used as a specific NIR contrast agent for noninvasive imaging of EGFr expression and monitoring of responses to molecularly targeted therapy.

Adenocarcinoma↗
PubMed2003

Real-time vital optical imaging of precancer using anti-epidermal growth factor receptor antibodies conjugated to gold nanoparticles.

Recent developments in photonic technology provide the ability to noninvasively image cells in vivo; these new cellular imaging technologies have the potential to dramatically improve the prevention, detection, and therapy of epithelial cancers. Endoscope-compatible microscopies, such as optical coherence tomography and reflectance confocal microscopy, image reflected light, providing a three-dimensional picture of tissue microanatomy with excellent spatial resolution (1-10 micro m). However, their ability to image molecular biomarkers associated with cancer is limited. Here, we describe a new class of molecular specific contrast agents for vital reflectance imaging based on gold nanoparticles attached to probe molecules with high affinity for specific cellular biomarkers. The application of gold bioconjugates for vital imaging of precancers is demonstrated using cancer cell suspensions, three-dimensional cell cultures, and normal and neoplastic fresh cervical biopsies. We show that gold conjugates can be delivered topically for imaging throughout the whole epithelium. These contrast agents have potential to extend the ability of vital reflectance microscopies for in vivo molecular imaging. They can potentially enable combined screening, detection, and therapy of disease using inexpensive imaging systems; such tools could allow mass screening of diseases such as cancer in resource-poor settings.

Antibodies, Monoclonal↗
PubMedDate not supplied

Structural and functional optical imaging of three-dimensional engineered tissue development.

A significant amount of the data collected by cell biologists and tissue engineers relies on invasive imaging techniques to visualize dynamic structural and functional properties in engineered tissues. We report the use of optical coherence tomography and the comparative use of confocal microscopy to nondestructively and noninvasively monitor the structural and functional characteristics of three-dimensional engineered tissues over time. The engineered tissue model is composed of chitosan scaffolds and fibroblasts transfected with vinculin fused to green fluorescent protein. We image the developmental process of engineered tissues from changes of tissue microarchitecture to cell-matrix adhesions in three dimensions. These findings demonstrate the potential for optical coherence tomography in applications in cell and tissue biology, tissue engineering, and drug discovery.

Animals↗
PubMed1997

Frequency-domain optical imaging of absorption and scattering distributions by a Born iterative method.

We presents a Born; iterative method, for reconstructing optical properties of turbid media by means of frequency-domain data. The approach is based on iterative solution of a linear perturbation equation, which is derived from the integral from of the Helmholtz wave equation for photon-density waves in each iteration the total field and the associated weight matrix are recalculated based on the previous reconstructed image. We then obtain a new estimate by solving the updated perturbation equation. The forward solution, also based on a Helmholtz equation, is obtained by a multigrid finite difference method. The inversion is carried out through a Tikhonov regularized optimization process by the conjugate gradient descent method. Using this method, we first reconstruct the distribution of the complex wave numbers in a test medium, from which the absorption and the scattering distributions are then derived. Simulation results with two-dimensional test media have shown that this method can yield quantitatively (in terms of coefficient valued) as well as qualitatively (in terms of object location and shape) accurate reconstructions of absorption and scattering distributions in cases in which the first-order Born approximation cannot work well. Both full-angle and limited-angle measurement schemes have been simulated to examine the effect of the location of detectors and sources. The robustness of the algorithm to noise has also been evaluated.

Absorption↗
PubMed2003

Fluorescence-enhanced optical imaging in large tissue volumes using a gain-modulated ICCD camera.

A novel image-intensified charge-coupled device (ICCD) imaging system has been developed to perform 3D fluorescence tomographic imaging in the frequency-domain using near-infrared contrast agents. The imager is unique since it (i) employs a large tissue-mimicking phantom, which is shaped and sized to resemble a female breast and part of the extended chest-wall region, and (ii) enables rapid data acquisition in the frequency-domain by using a gain-modulated ICCD camera. Diffusion model predictions are compared to experimental measurements using two different referencing schemes under two different experimental conditions of perfect and imperfect uptake of fluorescent agent into a target. From these experimental measurements, three-dimensional images of fluorescent absorption were reconstructed using a computationally efficient variant of the approximate extended Kalman filter algorithm. The current work represents the first time that 3D fluorescence-enhanced optical tomographic reconstructions have been achieved from experimental measurements of the time-dependent light propagation on a clinically relevant breast-shaped tissue phantom using a gain-modulated ICCD camera.

Biophysical Phenomena↗
PubMed2005

Simultaneous recording of task-induced changes in blood oxygenation, volume, and flow using diffuse optical imaging and arterial spin-labeling MRI.

Increased neural activity in brain tissue is accompanied by an array of supporting physiological processes, including increases in blood flow and the rates at which glucose and oxygen are consumed. These responses lead to secondary effects such as alterations in blood oxygenation and blood volume, and are ultimately the primary determinants of the amplitude and temporal signature of the blood oxygenation level-dependent (BOLD) signal used prevalently to map brain function. We have performed experiments using a combination of optical and MRI-based imaging methods to develop a more comprehensive picture of the physiological events accompanying activation of primary motor cortex during a finger apposition task. Temporal profiles for changes in tissue hemoglobin concentrations were qualitatively similar to those observed for MRI-based flow and oxygenation signals. Quantitative analysis of these signals revealed peak changes of +16 +/- 2% for HbO, -13 +/- 2% for HbR, +8 +/- 3% for total Hb, +83 +/- 9% for cerebral blood flow, and +1.4 +/- 0.1% for the BOLD MRI signal. A mass balance model was used to estimate the change in rate of oxidative metabolism implied by the optical and flow measurements, leading to a computed value of +47 +/- 5%. It should be noted that the optical and MRI observations may in general reflect changes over different volumes of tissue. The ratio of fractional changes in oxidative metabolism to fractional change in blood flow was found to be 0.56 +/- 0.08, in general agreement with previous studies of flow-metabolism coupling.

Arousal↗
PubMed1994

Computations of time-dependent photon migration for biomedical optical imaging.

In summary, Table II is a listing of the pitfalls and advantages of using Monte Carlo simulations and numerical solution of the diffusion equation to describe photon migration in tissues. Judicious use of these techniques to describe the solution to the forward imaging problem may allow determination of the best theoretical resolution and the smallest detectable volume for the range of optical property differences expected in situ or imposed by contrast agent administration. Furthermore, an understanding of the forward imaging problem through these numerical techniques also contributes to our understanding of the most efficient solution to the inverse imaging problem.

Algorithms↗
PubMed2001

Quantitative analysis of three-dimensional-resolved fiber architecture in heterogeneous skeletal muscle tissue using nmr and optical imaging methods.

The determination of principal fiber directions in structurally heterogeneous biological tissue substantially contributes to an understanding of its mechanical function in vivo. In this study we have depicted structural heterogeneity through the model of the mammalian tongue, a tissue comprised of a network of highly interwoven fibers responsible for producing numerous variations of shape and position. In order to characterize the three-dimensional-resolved microscopic myoarchitecture of the intrinsic musculature of the tongue, we viewed its fiber orientation at microscopic and macroscopic length scales using NMR (diffusion tensor MRI) and optical (two-photon microscopy) imaging methods. Diffusion tensor imaging (DTI) of the excised core region of the porcine tongue resulted in an array of 3D diffusion tensors, in which the leading eigenvector corresponded to the principal fiber orientation at each location in the tissue. Excised axially oriented lingual core tissues (fresh or paraffin-embedded) were also imaged with a mode-locked Ti-Sapphire laser, (76 MHz repetition rate, 150 femtosecond pulse width), allowing for the visualization of individual myofibers at in situ orientation. Fiber orientation was assessed by computing the 3D autocorrelation of discrete image volumes, and deriving the minimal eigenvector of the center voxel Hessian matrix. DTI of the fibers, comprising the intrinsic core of the tongue, demonstrated directional heterogeneity, with two distinct populations of fibers oriented orthogonal to each other and in-plane to the axial perspective. Microscopic analysis defined this structural heterogeneity as discrete regions of in-plane parallel fibers, with an angular separation of ~80 degrees, thereby recapitulating the macroscopic angular relationship. This analysis, conceived at two different length scales, demonstrates that the lingual core is a spatially complex tissue, composed of repeating orthogonally oriented and in-plane fiber patches, which are capable of jointly producing hydrostatic elongation and displacement.

Algorithms↗
PubMed2000

A 3-D reconstruction system for the human jaw using a sequence of optical images.

This paper presents a model-based vision system for dentistry that will assist in diagnosis, treatment planning, and surgical simulation. Dentistry requires an accurate three-dimensional (3-D) representation of the teeth and jaws for diagnostic and treatment purposes. The proposed integrated computer vision system constructs a 3-D model of the patient's dental occlusion using an intraoral video camera. A modified shape from shading (SFS) technique, using perspective projection and camera calibration, extracts the 3-D information from a sequence of two-dimensional (2-D) images of the jaw. Data fusion of range data and 3-D registration techniques develop the complete jaw model. Triangulation is then performed, and a solid 3-D model is reconstructed. The system performance is investigated using ground truth data, and the results show acceptable reconstruction accuracy.

Algorithms↗
PubMedDate not supplied

[Optical image processing in the analysis of the structural elements of the x-ray picture of the adult respiratory distress syndrome].

The paper is devoted to the potentialities of aposterior image processing in adult patients with the respiratory distress-syndrome (RDS). Thirty one cases of optical processing of radiograms were analyzed. Pulmonary changes were absent in 10 persons of the control group. The authors described spatial and frequency characteristics of the structural elements of an x-ray picture of RDS (change of interstitial tissue, the state of pulmonary markings, micro-atelectases, edematous and small hemorrhagic parts). The localization of disease is mostly peripheral. The authors paid attention to probable criteria of differential diagnosis between RDS and other conditions, manifesting themselves in clinically acute parenchymatous respiratory insufficiency (lung edema, acute pneumonia, thromboembolism of the pulmonary artery).

Densitometry↗