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At least 1,099 records · Page 61Linked to original sources
PubMed2000

Scanning Near-Field Optical Microscopy and Spectroscopy as a Tool for Chemical Analysis.

Research into the nanometer-scale region is currently of relevance in many branches of modern science and engineering, such as in microelectronics, supramolecular chemistry, and in a biological context. A great deal of attention is given to the design of molecular devices, usually towards understanding the function of existing "molecular machines". Central to this task are powerful diagnostic tools capable of recording chemical information with spatial resolution in the nanometer range. While elemental analysis of surfaces with a lateral resolution of a few dozen nanometers is almost routine, analysis of molecular species with a resolution of <1 µm is very difficult. Scanning-tunneling and atomic-force microscopies usually do not give any chemical information. By combining scanning near-field optical microscopy (SNOM)-the "optical member" of the family of scanning-probe microscopies-with optical spectroscopy, it is possible to obtain molecular information from sample areas as little as 50 nm in diameter. In SNOM, a light source is scanned above the object of interest at a distance of a few nanometers. In the optical near field, the illuminated area is not subject to the Abbé diffraction limit, but merely by the size of the illuminating source. High quality SNOM probes can be reproducibly prepared by a chemical-etching method. These etched probes have an optical transmission up to 1000-fold higher than commercial (pulled) SNOM tips and can withstand higher laser power. This last advantage allows not only high resolution optical imaging, but also localized spectroscopic investigations of surfaces and even optical "nanosampling" by pulsed-laser ablation. The ablated material can be transported over a considerable distance, which opens the possibility for its subsequent analysis with a complementary, highly sensitive analytical method, such as mass spectrometry.

Journal Article↗
PubMed2006

In vivo real-time vessel imaging and ex vivo 3D reconstruction of atherosclerotic plaque in apolipoprotein E-knockout mice using synchrotron radiation microscopy.

BACKGROUND: To examine the pathophysiology of atherosclerosis, imaging the vascular wall and pathology without tissue damage is required. We used the unmonochromatized synchrotron X-ray to acquire in vivo real-time and ex vivo images of atherosclerotic lesions in apo E-knockout mice without contrast agents or staining. METHODS: In the five apo E-knockout mice (apo E-/-, 12, 24, 32, 48, 62-week-old, 3 males) and age/sex matched five wild type mice on cow diets, we acquired in vivo real-time images of thoracic aorta without contrast agents and then, the central arterial trees were dissected intact. Ex vivo synchrotron images with tomographic reconstruction were done and compared with the corresponding pathology. RESULTS: For all living animals, in vivo real-time images of thoracic aorta could be acquired without contrast agents but could not identify the atherosclerotic lesions. Ex vivo images accurately determined aortic wall and atherosclerotic plaque without staining in comparison to histopathology according to the AHA classification (r=0.84, p<0.001). The volume rendered 3 D images of plaque showed central cholesterol clefts as matched with optical images. CONCLUSIONS: The combination of synchrotron enhanced X-ray microscopy and genetically engineered hyperlipidemic animals would be a useful tool to investigate the changes of advanced atherosclerotic lesions.

Animals↗
PubMed2003

Why is super-resolution so inefficient?

Many optical imaging systems have been designed to achieve spatial resolution exceeding the limit proposed by Abbe theory, namely lambda/2NA. These systems invariably use light inefficiently. We discuss the application of information theory to this problem, in an effort to find an upper limit to the theoretical efficiency of a super-resolving system, as a function of the degree to which its capabilities exceed the Abbe limit.

Image Enhancement↗
PubMed2006

Raman imaging and Kelvin probe microscopy for the examination of the heterogeneity of doping in polycrystalline boron-doped diamond electrodes.

The issue of the heterogeneity of boron doping in microcrystalline diamond films was addressed by four different methods: micro-Raman spectroscopy and Raman imaging, Kelvin probe force microscopy, conducting atomic force microscopy, and scanning electrochemical microscopy. The samples were commercially available films from Windsor Scientific, with an average boron concentration of about 5 x 10(20) cm(-3). In agreement with previous works, all of the methods showed that the boron uptake was nonuniform across the surface of the electrode. Two different types of regions were evidenced, with metallic or semiconducting properties that were characterized with different types of Raman spectra. The line shape of these spectra was strongly dependent on the excitation wavelength. Local variations in electroactivity were evidenced by the SECM curves, which are related to the electronic properties of the individual grains, which, in turn, are governed by the boron content of the individual crystallites. In this study, two different micro-Raman imaging techniques were used that reveal the grain structure of the films: the images constructed from the diamond line intensity perfectly reproduced the optical image obtained by illuminating the sample in reflection. The method also allows detection of the presence of nondiamond carbon, especially in the metallic parts of the samples. Other spectral features (intensity of the boron-related broad lines, as well as the frequency and width of the diamond line) were used to construct images. In every case, the grain structure of the film was revealed, as well as twinning within individual crystallites. All approaches revealed that no enhanced doping or boron depletion occurred at the grain boundaries.

Journal Article↗
PubMed1993

Voltage-sensitive magnetic gels as magnetic resonance monitoring agents.

Many polymer gels undergo a volume phase transition in electric fields. We report here the synthesis of a polyelectrolyte gel that incorporates magnetic particles of iron oxide into the polymer network; these particles couple the gel volume transition to the NMR relaxation times of the surrounding water. We find that the water proton relaxation rates (T2(-1)) in aqueous suspensions of particles of the magnetic gel increase significantly in an electric field. Such changes can also be induced by the hyperpolarization of red blood cells in the suspension, presumably as a result of the electric fields at the cell membrane surfaces. These gels may play a part in magnetic resonance imaging analogous to that of voltage-sensitive dyes in optical imaging.

Animals↗
PubMed2001

Non-optical tip-sample distance control method for scanning near-field optical microscopy using a piezoresistive micro cantilever.

A piezoresistive micro cantilever is applied to monitor the displacement of an optical fibre probe and to control tip-sample distance. The piezoresistive cantilever was originally made for a self-sensitive atomic force microscopy (AFM) probe and has dimensions of 400 microm length, 50 microm width and 5 microm thickness with a resistive strain sensor at the bottom of the cantilever. We attach the piezoresistive cantilever tip to the upper side of a vibrating bent optical fibre probe and monitor the resistance change amplitude of the strain sensor caused by the optical fibre displacement. By using this resistance change to control the tip-sample distance, the two-cantilever system successfully provides topographic and near-field optical images of standard samples in a scanning near-field optical microscopy (SNOM)/AFM system. A resonant characteristic of the two-cantilever system is also simulated using a mechanical model, and the results of simulation correspond to the experimental results of resonance characteristics.

Journal Article↗
PubMed2003

Molecular imaging of musculoskeletal diseases.

Chronic musculoskeletal diseases such as arthritis, malignancy, chronic injury/ inflammation, and chronic musculoskeletal pain often pose challenges for current clinical imaging modalities. There is hope that a growing field, referred to as "molecular imaging," will shed new light on these chronic phenomenon as it aims to noninvasively detect special molecular and physiologic effects such as metabolism rate, specific proteins, cell death, and particular gene-related events. Molecular imaging represents recent advances in imaging technology, engineering, chemistry, molecular biology, and genetics that have coalesced into a multidisciplinary and multimodality effort. Molecular probes are currently being developed not only in radionuclide-based techniques but also in magnetic resonance imaging, magnetic resonance spectroscopy, ultrasound, and the emerging field of optical imaging. Furthermore, molecular imagers are fueling the development of novel molecular therapies and gene therapy, as tracking these efforts in living subjects is now possible with molecular imaging protocols.

Animals↗
PubMed2006

Real-timereflectance confocal microscopy, a noninvasive tool for in vivo quantitative evaluation of comedolysis in the rhino mouse model.

BACKGROUND: Near-infrared reflectance confocal microscopy (RCM) is a noninvasive tool that provides real-time images of thin virtual horizontal tissue sections. AIMS/METHODS: We have used a rhino mouse model in combination with topical application of all-trans-retinoic acid and all-trans-retinol to investigate the usefulness of RCM as a noninvasive imaging tool to evaluate comedolysis in vivo and over time. Optical images were correlated with routine histology. RESULTS: Our results demonstrate that RCM in vivo can visualize the process of transformation of utriculi (pseudocomedones) towards a normal-appearing follicular structure during retinoid treatment. The retinoic acid intervention group showed a dose-related response, while the vehicle-treated group did not show utricular changes. CONCLUSIONS: RCM represents a useful tool for in vivo morphological and quantitative evaluation of skin utriculi over time and could be used as an adjunct tool to histopathological techniques for comedolysis studies.

Acne Vulgaris↗
PubMed2002

Molecular-genetic imaging: a nuclear medicine-based perspective.

Molecular imaging is a relatively new discipline, which developed over the past decade, initially driven by in situ reporter imaging technology. Noninvasive in vivo molecular-genetic imaging developed more recently and is based on nuclear (positron emission tomography [PET], gamma camera, autoradiography) imaging as well as magnetic resonance (MR) and in vivo optical imaging. Molecular-genetic imaging has its roots in both molecular biology and cell biology, as well as in new imaging technologies. The focus of this presentation will be nuclear-based molecular-genetic imaging, but it will comment on the value and utility of combining different imaging modalities. Nuclear-based molecular imaging can be viewed in terms of three different imaging strategies: (1) "indirect" reporter gene imaging; (2) "direct" imaging of endogenous molecules; or (3) "surrogate" or "bio-marker" imaging. Examples of each imaging strategy will be presented and discussed. The rapid growth of in vivo molecular imaging is due to the established base of in vivo imaging technologies, the established programs in molecular and cell biology, and the convergence of these disciplines. The development of versatile and sensitive assays that do not require tissue samples will be of considerable value for monitoring molecular-genetic and cellular processes in animal models of human disease, as well as for studies in human subjects in the future. Noninvasive imaging of molecular-genetic and cellular processes will complement established ex vivo molecular-biological assays that require tissue sampling, and will provide a spatial as well as a temporal dimension to our understanding of various diseases and disease processes.

Adoptive Transfer↗
PubMed1993

Confocal imaging of the alpha 6 and beta 4 integrin subunits in the human cornea with aging.

PURPOSE: The purpose of this study was to examine changes in the distribution of integrin subunits, alpha 6 and alpha 4, in the normal human cornea with age. METHODS: Thirty normal corneas were examined and divided into three groups; corneas from children younger than 2 years, corneas from adults 29 to 70 years, and corneas from adults older than 70 years. The corneas were frozen and the sections were cut, double-stained with monoclonal antibodies to the integrin subunits, and visualized with Texas Red or fluorescein using confocal laser scanning microscopy. Computer imaging was conducted to determine differences. RESULTS: The alpha 6 subunit was generally localized along the basal and lateral surfaces of basal epithelial cells and projected into Bowman's membrane. The beta 4 subunit was only present along the basal surface. Overall, the major age-related difference was the loss of continuous alpha 6 and beta 4 subunits along the basal surface of basal epithelial cells. When reconstructed images from corneas of individuals older than 70 years were optically sectioned en face, the alpha 6 subunit appeared discontinuous. If the same optical images were viewed from corneas of younger individuals, the staining was continuous. The number and distribution of hemidesmosomes along the basal lamina did not change with age in the corneas examined. CONCLUSIONS: Using computer imaging associated with confocal laser scanning microscopy, we have demonstrated that there is an age-related change in the localization of the alpha 6 and beta 4 subunits.

Adult↗
PubMed1998

[An imaging system and computer processing of digital images from the Tesla BS500 transmission electron microscope].

Original digital image acquiring system for electron microscope TESLA BS500 was developed. Optical image from yttriumgarnet monocrystal was captured by TV CCD bottom mounted camera and processed by computer with software Video TIP. Repeated image acquisition enabled substantial improving of signal/noise ratio. Image element of 42 microns diameter was achieved. The system is ready for additional innovation, especially with a high performance CCD camera.

Image Processing, Computer-Assisted↗
PubMed1996

Frequency-domain optical mammography: edge effect corrections.

We have investigated the problem of edge effects in laser-beam transillumination scanning of the human breast. Edge effects arise from tissue thickness variability along the scanned area, and from lateral photon losses through the sides of the breast. Edge effects can be effectively corrected in frequency-domain measurements by employing a two-step procedure: (1) use of the phase information to calculate an effective tissue thickness for each pixel location; (2) application of the knowledge of tissue thickness to calculate an edge-corrected optical image from the ac signal image. The measurements were conducted with a light mammography apparatus (LIMA) designed for feasibility tests in the clinical environment. Operating in the frequency-domain (110 MHz), this instrument performs a transillumination optical scan at two wavelengths (685 and 825 nm). We applied the proposed two-step procedure to data from breast phantoms and from human breasts. The processed images provide higher contrast and detectability in optical mammography with respect to raw data breast images.

Biophysical Phenomena↗
PubMedDate not supplied

Development of high-sensitivity near-infrared fluorescence imaging device for early cancer detection.

We have developed a high-sensitivity near-infrared (NIR) optical imaging system for noninvasive cancer detection based on the molecular-labeled fluorescent contrast agents. Recent developments in molecular beacons offer a way to selectively tag various precancer and cancer signatures and provide high tumor-to-background contrast. Near-infrared imaging can deeply probe tissue up to a couple of centimeters; thus, it possesses the potential for noninvasive detection of breast or lymph node cancer. A phase cancellation (in- and antiphase) device is used to increase the sensitivity in detecting fluorescent photons and the accuracy of tumor localization. The optoelectronic system consists of the laser diode sources, fiber optics, interference filter (to select the fluorescent photons), and the high-sensitivity photon detector (photomultiplier tube). The source-detector pair scans the tissue surface in multiple directions, and the localization image can be obtained by angular back-projection reconstruction. Simulations and experimental data demonstrated the feasibility of detection and localization offluorescent object embedded inside the highly scattering media. Tumor-bearing mouse model with injection of fluorescent contrast agents is used to simulate the human breast tumor labeled with molecular beacons. The system can detect fluorescent contrast agents as small as one nanomole at the depth of three centimeters, with a three-millimeter localization error. This instrument has the potential for tumor diagnosis and imaging, and the accuracy of the localization suggests that this system could help guide the clinical fine-needle biopsy. Also, this portable device would be complementary to x-ray mammography and provide add-on information on early diagnosis and localization of breast tumor.

Animals↗
PubMed2003

Thermoacoustic molecular imaging of small animals.

We have designed, constructed, and tested a thermoacoustic computed tomography (TCT) scanner for imaging optical absorption in small animals in three dimensions. The device utilizes pulsed laser irradiation (680-1064 nm) and a unique, 128-element transducer array. We quantified the isotropic spatial resolution of this scanner to be 0.35 mm. We describe a dual-wavelength subtraction technique for isolating optical dyes with TCT. Phantom experiments demonstrate that we can detect 5 fmol of a near-infrared dye (indocyanine green, ICG) in a 1-microL volume using dual-wavelength subtraction. Initial TCT imaging in phantoms and in two sacrificed mice suggests that three-dimensional, optical absorption patterns in small animals can be detected with an order of magnitude better spatial resolution and an order of magnitude better low-contrast detectability in small animals when compared to fluorescence imaging or diffusion optical tomography.

Algorithms↗
PubMed2005

Bioluminescent imaging of ubiquitin ligase activity: measuring Cdk2 activity in vivo through changes in p27 turnover.

Optical imaging of reporter molecules such as firefly luciferase has become a popular method of tracking and visualizing cells in living animals. Many biological processes involve ubiquitin ligases, which target specific proteins for destruction under specific sets of conditions. Importantly, the motifs recognized by different ubiquitin ligases are often modular and can be used to target foreign proteins for destruction in cis. We recently fused the Cdk inhibitor p27, which is polyubiquitylated by a Skp2-containing ubiquitin ligase if phosphorylated by cdk2 to firefly luciferase. The resulting fusion protein, p27-Luc, was induced by cdk2 inhibitors in living cells grown in culture or in nude mice. This article describes protocols for validation of p27-Luc in cell culture using siRNA against cdk2 (or its partner cyclin A) and for imaging cells producing p27-Luc grown in transparent hollow fibers after treatment with cdk2 inhibitory drugs in vivo. These approaches should be generalizable to other ubiquitin-ligase substrate pairs.

Animals↗
PubMed2002

Use of magnetic resonance imaging to differentiate optic neuritis and nonarteritic anterior ischemic optic neuropathy.

OBJECTIVE: To determine if magnetic resonance imaging (MRI) of the optic nerves obtained during the acute phase can distinguish patients with optic neuritis (ON) from those with nonarteritic anterior ischemic optic neuropathy (NAION). DESIGN: Retrospective, neuroradiologic, observational study. PARTICIPANTS: Sixty-four patients diagnosed as having either ON or NAION who were diagnosed by clinical criteria and imaged by MRI. METHODS: Demographic information on the MRI scans was masked and the patients were presented randomly and in a blinded fashion to a neuroradiologist (JDR) for determination of abnormalities. Reproducibility was assessed by presenting 10 of the scans a second time to the same neuroradiologist. MAIN OUTCOME MEASURES: The presence or absence and location of abnormal MRI signals of the optic nerve. RESULTS: Evaluation of reproducibility revealed identical interpretations of the ten scans submitted a second time. The optic nerve was abnormal in the clinically affected eye in 31 of the 32 ON patients but in only 5 of the 32 NAION patients. Thirty of the 31 ON patients who received gadolinium had enhancement, and 27 of the 32 ON patients had increased short T(1) inversion recovery signal in the clinically affected optic nerve. The five NAION patients with abnormal scans in the clinically affected eye had increased short T(1) inversion recovery signal, and in two of these, there also was enhancement of the optic nerve. For the ON patients, enhancement involved the entire length of the intraorbital optic nerve in 18 cases and the intracranial segment of the optic nerve in 19 cases. CONCLUSIONS: Our study shows that MRI scanning of the optic nerve shows significantly different results between patients clinically diagnosed with either ON or NAION.

Acute Disease↗
PubMed1989

High-resolution image recovery from image-plane arrays, using convex projections.

We consider the problem of reconstructing remotely obtained images from image-plane detector arrays. Although the individual detectors may be larger than the blur spot of the imaging optics, high-resolution reconstructions can be obtained by scanning or rotating the image with respect to the detector. As an alternative to matrix inversion or least-squares estimation [Appl. Opt. 26, 3615 (1987)], the method of convex projections is proposed. We show that readily obtained prior knowledge can be used to obtain good-quality imagery with reduced data. The effect of noise on the reconstruction process is considered.

Algorithms↗
PubMedDate not supplied

Adaptive spectral apodization for sidelobe reduction in optical coherence tomography images.

Often in imaging systems, the bandpass of the system is not uniform. In temporal coherence imaging methods such as optical coherence tomography, one would like to achieve the most spatially confined impulse response possible with a given source spectrum, minimizing sidelobes that blur adjacent features together. Typically the spectrum of the source is controlled in order to remove sidelobes from the measured interferogram. However, the measured interferogram is not necessarily the best estimate of the scattering density of the object. In this work, a sidelobe supression method is proposed and demonstrated to achieve low sidelobes even with highly nonuniform, non-Gaussian spectra.

Algorithms↗