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Results for “Optical imaging”

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At least 361 records · Page 20Linked to original sources
PubMed2005

Near-field optical imaging of plasmon modes in gold nanorods.

We have investigated optical properties of single gold nanorods by using an apertured-type scanning near-field optical microscope. Near-field transmission spectrum of single gold nanorod shows several longitudinal surface plasmon resonances. Transmission images observed at these resonance wavelengths show oscillating pattern along the long axis of the nanorod. The number of oscillation increases with decrement of observing wavelength. These spatial characteristics were well reproduced by calculated local density-of-states maps and were attributed to spatial characteristics of plasmon modes inside the nanorods. Dispersion relation for plasmons in gold nanorods was obtained by plotting the resonance frequencies of the plasmon modes versus the wave vectors obtained from the transmission images.

Journal Article↗
PubMed2005

Fine functional organization of auditory cortex revealed by Fourier optical imaging.

We provide an overall view of the functional tonotopic organization of the auditory cortex in the rat. We apply a recently developed technique for acquiring intrinsic signal optical maps, Fourier imaging, in the rat auditory cortex. These highly detailed maps, derived in a several-minute-long recording procedure, delineate multiple auditory cortical areas and demonstrate their shapes, sizes, and tonotopic order. Beyond the primary auditory cortex, there are at least three distinct areas with fine-scale tonotopic organization, as well as at least one additional high-frequency field. The arrangement of all of these cortical areas is consistent across subjects. The accuracy of these optical maps was confirmed by microelectrode mapping in the same subjects. This imaging method allows fast mapping of the auditory cortex at high spatial resolution comparable to that provided by conventional microelectrode technique. Although spiking activity is largely responsible for the evoked intrinsic signals, certain features of the optical signal cannot be explained by spiking activity only, and should probably be attributed to other mechanisms inducing metabolic activity, such as subthreshold membrane phenomena.

Animals↗
PubMed2004

Superresolution of three-dimensional optical imaging by use of evanescent waves.

We simulate a three-dimensional optical diffraction tomography experiment in which superresolution is achieved by illuminating the object with evanescent waves generated by a prism. We show that accounting for multiple scattering between the object and the prism interface is mandatory to obtain superresolved images. Because the Born approximation leads to poor results, we propose a nonlinear inversion method for retrieving the map of permittivity of the object from the scattered far field. We analyze the sensitivity to noise of our algorithm and point out the importance of using incident propagative waves together with evanescent waves to improve the robustness of the reconstruction without losing the superresolution.

Algorithms↗
PubMedDate not supplied

[A study of digital x-ray detection systems with optical image transfer].

The work describes the performance characteristics of roentgenographic screen-optics-CCD-matrix systems based on the KRTs-1 digital roentgenographic system developed at SpektrAp, Ltd. The efficiency of X-ray detection is estimated from the minimum detectable contrast and maximum resolution. The effect of the X-ray imaging system components on the efficiency of detection is studied. The X-ray screen structure is shown to have a crucial effect on the efficiency of detection as estimated from the image resolution.

Optics and Photonics↗
PubMedDate not supplied

[Optic coherent tomography: a new high-resolution technology of visualization of tissue structures. Communication II. Optical images of benign and malignant entities].

This is the second communication of a series of publications on Russian studies in the field of optical coherent tomography (OCT), the newest noninvasive highly resolving technology of visualization of the structure of biological tissues. By using the investing tissues as an example, this paper demonstrates the universal types of changes in their optical properties. Optimal images permit differentiate benign and malignant processes with a high degree of diagnostic accuracy. Diverse benign processes occurring in the epithelium are detected on the OCT images as changes in its height, the scattering properties and stroke of a basilar membrane. The absence of any structure on the image is the main OCT criterion for malignancy. The diagnostic efficiency of OCT is high in recognizing neoplasia of various mucous membranes: the sensitivity of the technique is 77-98%; its specificity and diagnostic accuracy are 71-96 and 81-87%, respectively.

Adult↗
PubMed2001

Direct interpretation of near-field optical images.

The interpretation of the detection process in near-field optical microscopy is reviewed on the basis of a discussion about the possibility of establishing direct comparisons between experimental images and the solutions of Maxwell equations or the electromagnetic local density of states. On the basis of simple physical arguments, it is expected that the solutions of Maxwell equations should agree with images obtained by collecting mode near-field microscopes, while the electromagnetic local density of states should be considered to provide a practical interpretation of illumination mode near-field microscopes. We review collecting mode near-field microscope images where the conditions to obtain good agreement with the solutions of Maxwell equations have indeed been identified. In this context of collecting mode near-field microscopes, a fundamentally different functionality between dielectric and gold-coated tips has been clearly identified experimentally by checking against the solutions of Maxwell equations. It turns out that dielectric tips detect a signal proportional to the optical electric field intensity, whereas gold-coated tips detect a signal proportional to the optical magnetic field intensity. The possible implications of this surprising phenomenon are discussed.

Journal Article↗
PubMed2005

Pulsed acousto-optic imaging in dynamic scattering media with heterodyne parallel speckle detection.

We present a new detection scheme for acousto-optic tomography based on pulsed-wave ultrasound and illumination combined with heterodyne parallel speckle detection. This setup can perform tomographies inside several-centimeter-thick scattering samples. Test experiments confirm the suitability of this method for performing tomographies inside various types of optically scattering media, including liquids.

Acoustics↗
PubMedDate not supplied

Improved excitation light rejection enhances small-animal fluorescent optical imaging.

Small-animal fluorescence-enhanced imaging involves the detection of weak fluorescent signals emanating from nanomolar to picomolar concentrations of exogenous or endogenously produced fluorophore concurrent with the rejection of an overwhelmingly large component of backscattered excitation light. The elimination of the back-reflected excitation light of the collected signal remains a major and often unrecognized challenge for further reducing the noise floor and increasing sensitivity of small-animal fluorescence imaging. Herein, we show that the combination of three-cavity interference and holographic super notch filters with appropriate imaging lenses to collimate light improves rejection of excitation light, enabling more accurate imaging. To assess excitation leakage, the "out-of-band (S(lambda x))" to "in-band (S(lambda m) - S(lambda x))" signal ratio from phantom studies and the target-to-background ratio (TBR) from in vivo animal imaging was acquired with and without collimating optics. The addition of collimating optics resulted in a 51% to 75% reduction in the ratio of (S(lambda x))/(S(lambda m) - S(lambda x)) for the phantom studies and an improvement of TBR from 11% to 31% and of signal-to-noise ratio from 11% to 142% for an integrin-targeting conjugate in human glioma xenografts.

Animals↗
PubMed2001

Depolarization and blurring of optical images by biological tissue.

We present a study of the image blurring and depolarization resulting from the transmission of a narrow beam of light through a continuous random medium. We investigate the dependence of image quality degradation and of depolarization on optical thickness, correlation length of the inhomogeneities, and incident polarization state. This is done numerically with a Monte Carlo method based on a transport equation that takes into account polarization of light. We compare our results with those for transport in media with discrete spherical scatterers. We show that depolarization effects are different in these two models of biological tissue.

Lasers↗
PubMed1999

Ultraresolution in optical imaging using spatiotemporal scanning.

Spatial information exceeding the passband of an imaging system can be captured by using the optics to generate a spatiotemporal multiple beam interference pattern that is scanned over the object, rather than using it to image the object directly. The modulation of the higher temporal harmonics of the signal resulting from collecting the scattered light represents a mapping in the time domain of higher spatial harmonics of the data. Upon reconstruction, the additional temporal degrees of freedom are mapped back in the spatial domain where they represent spatial frequencies exceeding the passband of the optics. The spatial resolution is thus not limited by the spatial passband, but rather by the temporal bandwidth of the detection system. Due to hardware limitations, experimental demonstration is provided only for a one-dimensional scan of Ronchi gratings with 50 and 200 lines per inch.

Journal Article↗
PubMed2004

Laser guide star adaptive optics imaging polarimetry of Herbig Ae/Be stars.

We have used laser guide star adaptive optics and a near-infrared dual-channel imaging polarimeter to observe light scattered in the circumstellar environment of Herbig Ae/Be stars on scales of 100 to 300 astronomical units. We revealed a strongly polarized, biconical nebula 10 arc seconds (6000 astronomical units) in diameter around the star LkHalpha 198 and also observed a polarized jet-like feature associated with the deeply embedded source LkHalpha 198-IR. The star LkHalpha 233 presents a narrow, unpolarized dark lane consistent with an optically thick circumstellar disk blocking our direct view of the star. These data show that the lower-mass T Tauri and intermediate mass Herbig Ae/Be stars share a common evolutionary sequence.

Journal Article↗
PubMed2006

High-resolution apertureless near-field optical imaging using gold nanosphere probes.

An apertureless near-field scanning optical microscope (ANSOM) that utilizes the enhanced field around a gold nanosphere, which is attached to the end of an atomic force microscope (AFM) tip, is used to image the local dielectric constant of the patterned metallic surfaces and local electric field around plasmonic nanosphere samples. A colloidal gold nanosphere (approximately 50 nm diameter) is linked to the extremity of the conventional etched-silicon probe. The scattering of laser radiation (633 or 532 nm) is modulated by the oscillating nanosphere-functionalized silicon tip, and the scattered radiation is detected. The approach curve (scattering intensity as a function of the tip-sample distance), the polarization dependence (scattering intensity as a function of the excitation polarization direction), and ANSOM image contrast confirm that the spherical nanosphere attached to the silicon tip acts as a point dipole that interacts with the sample surface via a dipole-dipole coupling, in which the dipole created by the field at the tip interacts with its own image dipole in the sample. The image obtained with the nanoparticle functionalized tip provides a dielectric map of the sample surface with a spatial resolution better than 80 nm. In addition, we show that the functionalized tip is capable of imaging the local electric field distribution above the plasmonic nanosphere samples. Overall, the result shows that high-resolution ANSOM is possible without the aid of the lightning-rod effect. With an improved tip-fabrication method, we believe that the method can provide a versatile high-resolution chemical imaging that is not available from usual forms of ANSOM.

Journal Article↗
PubMed1999

Analysis of Probe-Sample Interaction in Near-field Optical Image of Dielectric Structures.

: A two-dimensional formalism is provided for analyzing the probe-sample interaction of optical near-field images in transmission mode. The numerical simulation is performed on a dielectric surface with sub-wavelength structures. The constant-height, near-field intensity through two Gaussian ridges has been calculated for p-polarized incident light. The influence on the signal by the dielectric function of the probe, the size of the scatterers, and the angle of incidence is investigated. The passive probe model is compared when equipped with and without the tip and the near-field intensity is simultaneously calculated.

Journal Article↗
PubMed1996

High-speed optical imaging of afferent flow through rat olfactory bulb slices: voltage-sensitive dye signals reveal periglomerular cell activity.

Fast, multiple-site optical recording and video imaging techniques were combined to visualize the olfactory processing stream as it flowed through rat olfactory bulb slices stained with the voltage-sensitive dye RH155. A 464 element photodiode detector array was used to record the voltage-sensitive dye signals. Focal electrical stimulation of the olfactory nerve layer evoked relatively large optical responses in the olfactory nerve and glomerular layers but only small responses within the external plexiform layer. With paired-pulse stimulation, glomerular attenuation was evident in signals recorded from the glomerular and external plexiform layers but not from the olfactory nerve layer. At very high recording speeds ( < 0.2 msec/frame), the presynaptic component of the olfactory processing stream could be followed as it flowed through the olfactory nerve layer and into the glomerular layer, where its amplitude rapidly declined. This decline was followed by a reciprocal rise in a postsynaptic depolarization that was largely restricted to the glomerular layer. Spatiotemporal interactions between overlapping afferent streams within the glomerular layer were observed and partially characterized. The optically recorded glomerular layer response was largely resistant to bath application of GABAA receptor antagonists but was sensitive to manipulations of external chloride concentration and to bath application of a stilbene derivative, 4-acetamido-4'isothiocyanatostilbene-2,2'-disulfonic acid known to block Cl- conductances. It is suggested the the voltage-sensitive dye signals recorded from the glomerular layer reflect activity in periglomerular cells and that Cl- efflux through non-GABAA chloride channels contributes to the postsynaptic depolarization of these cells after olfactory nerve stimulation.

Afferent Pathways↗
PubMed2004

Optical imaging of breast tumor through temporal log-slope difference mappings.

A novel optical temporal log-slope difference mapping approach is proposed for cancerous breast tumor detection. In this method, target tissues are illuminated by near-infrared (700-1000 nm) ultrashort laser pulses from various surface source points, and backscattered time-resolved light signals are collected at the same surface points. By analyzing the log-slopes of decaying signals over all points on the source-detection grid, a log-slope distribution on the surface is obtained. After administration of absorption contrast agents, the presence of cancerous tumors increases the decaying steepness of the transient signals. The mapping of log-slope difference between native tissue and absorption-enhanced cancerous tissue indicates the location and projection of tumors on the detection surface. In this paper, we examine this method in the detection of breast tumors in two model tissue phantoms through computer simulation. The first model has a spherical tumor of 6mm in diameter embedded at the tissue center. The second model is a large tissue phantom embedded with a non-centered spherical tumor 8mm in diameter. Monte Carlo methods were employed to simulate the light transport and signal measurement. It is shown that the tumor in both the tissue models will be accurately projected on the detection surface by the proposed log-slope difference mapping method. The image processing is very fast and does not require any inverse optimization in image reconstruction.

Breast Neoplasms↗
PubMed2003

Shot-noise detection of ultrasound-tagged photons in ultrasound-modulated optical imaging.

We propose a new detection method for ultrasound-modulated optical tomography that allows us to perform parallel speckle detection with optimum shot-noise sensitivity, using a CCD camera. Moreover, we show that making use of a spatial filter system allows us to fully filter out speckle decorrelation noise. This method is confirmed by a test experiment.

Journal Article↗
PubMed2006

Optical imaging of dose distributions in Fricke gels.

Ferrous-sulphate infused gels, or 'Fricke gels', encounter great interest in the field of radiation dosimetry, due to their potential for 3D radiation dose mapping. Typically, magnetic resonance (MR) relaxation rates are determined in these systems in order to derive the absorbed dose. However, when large concentration gradients are present, diffusion effects before and during the MR imaging may not be negligible. In these cases, optical techniques may represent a viable alternative. This paper describes research aimed at measuring 3D dose distributions in a Fricke-xylenol orange gel by measuring optical density with a CCD camera. This method is inexpensive and fast. A series of early experiments is described, in which optical density profiles were measured with a commercial microdensitometer for film dosimetry. The light box of the device was modified to work at 567 nm, close to the maximum absorbance of the ferric ion-xylenol orange complex. Under these conditions, the gel shows linearity with dose and high sensitivity.

Dose-Response Relationship, Radiation↗