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At least 199 records · Page 11Linked to original sources
PubMed2005

X-Ray microanalytical techniques based on synchrotron radiation.

The development of 3rd generation synchrotron radiation sources like European Synchrotron Radiation Facility (ESRF) in parallel with recent advances in the technology of X-ray microfocusing elements like Kirkpatrick-Baez (KB) mirrors, diffractive (Fresnel zone plates, FZP) and refractive (compound refractive lenses, CRL) optics, makes it possible to use X-ray microscopy techniques with high energy X-rays (energy superior to 4 keV). Spectroscopy, imaging, tomography and diffraction studies of samples with hard X-rays at micrometre and sub-micrometre spatial resolutions are now possible. The concept of combining these techniques as a high-energy microscopy has been proposed and successfully realized at the ESRF beamlines. Therefore a short summary of X-ray microscopy techniques is presented first. The main emphasis will be put on those methods which aim to produce sub-micron and nanometre resolution. These methods fall into three broad categories: reflective, refractive and diffractive optics. The basic principles and recent achievements will be discussed for all optical devices. Recent applications of synchrotron based microanalytical techniques to characterise radioactive fuel particles (UO(2)) released from the Chernobyl reactor are reported.

Environmental Monitoring↗
PubMed2004

Performance of electronic portal imaging devices (EPIDs) used in radiotherapy: image quality and dose measurements.

The aim of our study was to compare the image and dosimetric quality of two different imaging systems. The first one is a fluoroscopic electronic portal imaging device (first generation), while the second is based on an amorphous silicon flat-panel array (second generation). The parameters describing image quality include spatial resolution [modulation transfer function (MTF)], noise [noise power spectrum (NPS)], and signal-to-noise transfer [detective quantum efficiency (DQE)]. The dosimetric measurements were compared with ionization chamber as well as with film measurements. The response of the flat-panel imager and the fluoroscopic-optical device was determined performing a two-step Monte Carlo simulation. All measurements were performed in a 6 MV linear accelerator photon beam. The resolution (MTF) of the fluoroscopic device (f 1/2 = 0.3 mm(-1)) is larger than of the amorphous silicon based system (f 1/2 = 0.21 mm(-1)), which is due to the missing backscattered photons and the smaller pixel size. The noise measurements (NPS) show the correlation of neighboring pixels of the amorphous silicon electronic portal imaging device, whereas the NPS of the fluoroscopic system is frequency independent. At zero spatial frequency the DQE of the flat-panel imager has a value of 0.008 (0.8%). Due to the minor frequency dependency this device may be almost x-ray quantum limited. Monte Carlo simulations verified these characteristics. For the fluoroscopic imaging system the DQE at low frequencies is about 0.0008 (0.08%) and degrades with higher frequencies. Dose measurements with the flat-panel imager revealed that images can only be directly converted to portal dose images, if scatter can be neglected. Thus objects distant to the detector (e.g., inhomogeneous dose distribution generated by a modificator) can be verified dosimetrically, while objects close to a detector (e.g., a patient) cannot be verified directly and must be scatter corrected prior to verification. This is justified by the response of the flat-panel imaging device revealing a strong dependency at low energies.

Equipment Failure Analysis↗
PubMed1990

In vivo chemical sensors for intensive-care monitoring.

There is a need for rapid assessment of a patient's biochemical status during intensive care so that therapies may be optimised. Chemical sensors for key species have the potential to allow continuous in vivo monitoring, and some progress is being made with certain sensors. Gases, ions and certain catabolites such as glucose and urea may be measured with devices based on mass spectrometric, electrochemical or optical principles. The physical form, and size of sensors must be matched to the measurement site, which can include the airway, the intravascular space, tissue and the skin surface. Electrochemical sensors for measurement of O2, pH and glucose have been the most widely used to date, although fibre-optic devices are currently attracting considerable interest. Invasive sensors still suffer from the problem of poor biocompatibility, particularly devices used in arteries and veins. Noninvasive methods may be successful in certain circumstances and in some patient groups, but peripheral measurements are often significantly influenced by circulatory phenomena such as shock. Further research is required if these limitations of both invasive and noninvasive sensors are to be overcome and continuous chemical monitoring is to be established as a routine clinical technique.

Biocompatible Materials↗
PubMedDate not supplied

Adenomas and carcinomas may be histologically detected in apparently normal colonic mucosa. A study of carcinogen-treated rats.

Clinical reports indicate that colonic neoplasias may be overlooked at colonoscopy. We investigated, in an experimental model, whether both gross and high power microscopical examinations could detect all induced colonic neoplasias. Forty-nine Sprague-Dawley rats received 1,2-dimethylhydrazine for 27 weeks. The colons were scrutinized grossly and at high-power microscopy complemented with chromoscopy. Biopsies were obtained from all mucosal alterations seen at gross and at high power microscopy. The gross examination of the colonic specimens in the 49 animals revealed 196 polyps or suspected polyps. Histology showed that 85.2% (167 out of 196) were adenomas or adenocarcinomas. The remnant polyp-free colons were subsequently examined by high-power stereo microscopy (46 magnifications). Fifty-five new lesions were detected and removed. Histology showed 48.9% (n = 24) additional neoplastic lesions in the 49 colon specimens. The remnant polyp-free colons were subsequently processed for histology. The sections showed 57 additional neoplastic lesions in the 49 colon specimens: 93.0% (n = 53) were adenomas (n = 35) and crypt dysplasias (n = 18), while the remaining 7.0% (n = 4) were invasive carcinomas. Experimentally-induced colonic neoplasias may be overlooked even after a careful scrutiny of the colonic mucosa using high-power optical devices.

1,2-Dimethylhydrazine↗
PubMed2004

Enhancement of nonlinear effects using photonic crystals.

The quest for all-optical signal processing is generally deemed to be impractical because optical nonlinearities are usually weak. The emerging field of nonlinear photonic crystals seems destined to change this view dramatically. Theoretical considerations show that all-optical devices using photonic crystal designs promise to be smaller than the wavelength of light, and to operate with bandwidths that are very difficult to achieve electronically. When created in commonly used materials, these devices could operate at powers of only a few milliwatts. Moreover, if these designs are combined with materials and systems that support electromagnetically induced transparency, operation at single-photon power levels could be feasible.

Crystallization↗
PubMed1993

Cognition-activated low-frequency modulation of light absorption in human brain.

Animal model studies indicate light-absorption changes of the exposed animal brain in response to visual stimulation. Here we report observations of red-light absorbance changes, attributable to repetitive blood concentration changes in response to stimulation in the human brain frontal region by a cognitive process. These responses are observed as low-frequency recurrence of changes by Fourier transform analysis and are attributed to blood concentration change stimulated by the increased metabolic rate of brain tissue in cognitive function. A simple, portable dual wavelength spectrophotometer was attached noninvasively to the human forehead to measure the low frequency and power spectra of fluctuations of absorbances attributed to variations of brain blood concentration in the frontal region. The responses are associated with brain activity in responses to problem solving of analogies presented visually that require an associative function in the frontal region. The method of subtraction of test -rest Fourier transforms minimizes the arterial pulse frequency contributions and identifies specific frequencies--for example, 0.8, 1.6, 1.8 Hz in 24 of 28 tests of nine individuals (85%). Tests in which no increased brain activity was elicited (rest-rest) showed small differences. It is concluded that low-frequency recurrences of brain activity linked to blood concentration increases can be detected in human subjects with an optical device of potentially for simplified tests of cognitive function in the 0- to 3-Hz region and with modifications for wider band recordings in localized tissue volumes by time-resolved spectroscopy.

Adolescent↗
PubMedDate not supplied

Modulation of an optical needle's reflectivity alters the average photon path through scattering media.

We introduce the concept of deliberate placement of absorbers to alter the average path of photons through tissue for a biomedical optical device. By changing the reflectivity of a needle that separates a source and detector, the average photon path through a turbid medium can be changed. Totally reflective needles have photon scattering density functions similar to a point source and detector in an infinite medium. An absorbing needle moves the average photon path of photons that reach the detector away from the needle. Thus, by modulating the reflectivity of the needle, it is possible to modify the sensitive volume, and simple tomography data should be possible. These results are confirmed by Monte Carlo simulations and experiment. Experiments include moving a black target relative to an optical "needle" and measuring the resulting intensity and phase lag of light reaching a detector at the distal end of the needle.

Biopsy↗
PubMed1987

[Possibilities and limits of marking the visual axis of the cornea using the surgical microscope].

In procedures involving refractive corneal surgery, as in the fitting of conventional optical devices for visual correction, the question of correct centering arises, i.e., the surgeon has to determine and mark the point of intersection of the visual axis on the cornea. The operating microscope, which is in any case used for the surgical procedure, provides the simple means of performing this task. The practical application of this procedure, the theory behind it, and suggestions as to possible instrumentation are the subject of this paper.

Cornea↗
PubMed1991

Dual-view microscopy with a single camera: real-time imaging of molecular orientations and calcium.

A new microscope technique, termed "W" (double view video) microscopy, enables simultaneous observation of two different images of an object through a single video camera or by eye. The image pair may, for example, be transmission and fluorescence, fluorescence at different wavelengths, or mutually perpendicular components of polarized fluorescence. Any video microscope can be converted into a dual imager by simple insertion of a small optical device. The continuous appearance of the dual image assures the best time resolution in existing and future video microscopes. As an application, orientations of actin protomers in individual, moving actin filaments have been imaged at the video rate. Asymmetric calcium influxes into a cell exposed to an intense electric pulse have also been visualized.

Actin Cytoskeleton↗
PubMed1985

Dual nature of the peaks of light scattered during spreading depression in chick retina.

In this work some physical properties of the optical concomitants of spreading depression (SD) are investigated in isolated chick retinas. The two peaks of light scattering during the phenomenon were studied at various wavelengths of the illuminating light. It was shown that the first fast increase in light scattering is highly dependent on the wavelength and seems to be a "blue" scattering. The second slow peak, not so dependent, behaves as a "white" scattering. This implies in different underlying physical mechanisms for the two peaks. Based in this dissimilar behavior, using appropriate optical device and adding some substances to the maintaining Ringer solution it could be observed that the death of tissue is accompanied by a light scattering change comparable to the first peak of SD. The opalescence of the second peak is more similar to the opalescence caused by addition of NaCl to the Ringer in which the fragment of retina is maintained.

Animals↗
PubMed1998

[Stereo display of MR angiograms].

PURPOSE: To provide methods for stereoscopic visual demonstration from 3D reconstructed MR angiographic images. METHODS: Stereoscopic viewing can be obtained with pairs of images that are displayed at angles of 15 degrees. Optical devices as stereoscopic binoculars or minor stereoscopes facilitate stereoscopic viewing. The possibility of stereoscopic projections for a larger auditorium is mentioned. RESULTS: Using three clinical examples the advantages of stereoscopic display of MR angiograms are demonstrated. CONCLUSIONS: MR angiography allows stereoscopic viewing with simple methods, like CT- and conventional rotation angiography. This principle, which has been known for 100 years, may thus acquire a new significance.

Adult↗
PubMed1994

[The phasic imaging of velopharyngeal sphincter movements].

The velopharyngeal function while swallowing water was studied on a healthy volunteer patient with velopharyngeal closure and on a patient with velopharyngeal insufficiency. This patient suffers from open hypernasality as a result of shortened velum. Both subjects underwent nasoendoscopy with a flexible fiber glass optical device while swallowing water and while articulating the plosive consonant /k/. Velopharyngeal function was documented by means of videotaping and then the single video images were placed together along a time scale to form a new temporal image. This image makes possible a quick and comprehensive differentiation between physiological and disturbed motion patterns as demonstrated in this study using velopharyngeal function as the example. The videotaping in lapse time of such disordered movements can provide indicators of the therapeutical steps to be taken.

Adult↗
PubMed2007

Multicolor single-molecule spectroscopy with alternating laser excitation for the investigation of interactions and dynamics.

We have developed confocal multicolor single-molecule spectroscopy with optimized detection sensitivity on three spectrally distinct channels for the study of biomolecular interactions and FRET between more than two molecules. Using programmable acousto-optical devices as beamsplitter and excitation filter, we overcome some of the limitations of conventional multichroic beamsplitters and implement rapid alternation between three laser lines. This enables to visualize the synthesis of DNA three-way junctions on a single-molecule basis and to resolve seven stoichiometric subpopulations as well as to quantify FRET in the presence of competing energy transfer pathways. Furthermore, the ability to study correlated molecular movements by monitoring several distances within a biomolecular complex simultaneously is demonstrated.

Color↗
PubMed1998

Instrumentation for the diagnosis of term and preterm labour.

The problems associated with labor during pregnancy are among the most important health issues facing physicians. Understanding the role of the uterus and cervix in labor and developing methods to control their function is essential to solving problems relating to labor. At the moment, only crude, inaccurate and subjective methods are used to assess changes in the uterus and cervix that occur in preparation for or during labor. In the past several years, we have developed noninvasive methods to quantitatively evaluate the uterus and cervix based respectively on recording of uterine electrical signals from the abdominal surface (uterine EMG) and measurement of light-induced cervical collagen fluorescence (LIF) with an optical device (Collascope). The methods are rapid and allow assessment of uterine contractility and cervical ripening. Studies in rats and humans indicate that uterine and cervical function can be successfully monitored during pregnancy using these approaches and that these techniques might be used in a variety of conditions associated with labor to better define management. The potential benefits of the proposed instrumentation and methods include a reducing the rate of preterm delivery, improving maternal and perinatal outcome, monitoring treatment, decreasing cesarean section rate and improving research methods to understand uterine and cervical function.

Animals↗
PubMed1989

The Erlangen micro-lightguide spectrophotometer EMPHO I.

The Erlangen micro-lightguide spectrophotometer EMPHO 1 was designed for fast diffuse reflection (remission) spectrophotometry in small tissue volumes. The aim was to construct a compact, modular instrument with a high repetition rate which can be adapted to moving organs, e.g. the beating heart in situ, by the use of highly flexible micro-lightguides. Focusing problems, which cannot be solved when conventional optical devices such as microscopes are used in moving tissues, become negligible. A bandpass interference filter disk, which is rotated by a motor serves as a monochromating unit. One diffuse reflection spectrum in a selected wavelength domain is recorded during each revolution of the motor. Special filter disks, with spectral ranges of 400-520, 500-630, 600-1200 nm can be used for different tasks. The monochromated light is transmitted by means of a flexible fluid-lightguide to a photomultiplier tube. The electrical signal, which is proportional to the light intensity is recorded by an IBM-compatible AT. An analogue to digital converter has been developed for the AD conversion. Sampling of the spectra occurs in steps of 2 nm triggered by a decoding unit, containing an EPROM where the function between the wavelength-angular position characteristic of the filter disk is stored. A decoder wheel mounted on the same axle as the driving motor is used to program the decoder unit and to recall the wavelength position function. The decoding procedure enables a high wavelength reproducibility to be attained. The monochromating device allows a sampling velocity of 100 spectra per second. The EMPHO I has been successfully applied to experiments in the beating heart, the brain, the eye, the liver, the small intestine and the skeletal muscle of mammals. First investigations have also been performed in the heart during open heart surgery and in human skin. The apparatus has a high sampling rate and the small catchment volume allows measurements of remission spectra in tissue volumes supplied by only a few capillaries. The absolute oxygenation and the relative haemoglobin concentration can be determined by on-line computer evaluation of the recorded spectra and displayed on a screen.

Animals↗
PubMed1997

Evanescent (tunneling) photon and cellular "vision'.

The existence of a rudimentary form of cellular 'vision' was discovered experimentally by Albrecht-Buehler. He found that Swiss 3T3 cells approached distant infrared light spots and suggested that the most likely explanation for this phenomenon involves the long-range processing of electromagnetic signals by the cells. In this paper, a theoretical possibility of this phenomenon is presented within the fully quantum theoretical framework of the electromagnetic field and water. By taking into account the usually neglected interaction between the electric dipole field of water molecules and the quantized electromagnetic field, the dynamically ordered region of water surrounding the cell up to the coherence length < 50 microns is shown to play the role of a nonlinear coherent optical device through which the cells receive electromagnetic signals from distant light spots. The electromagnetic signals for the cell Albrecht-Buehler found are shown to consist of evanescent photons (i.e. soft polaritons) tunneling through the dynamically ordered region of water between the cell and the distant light spot. In contrast to the (normal) vision of animals realized by receiving (normal) photons, cellular "vision' is found to be realized by receiving evanescent photons. It is also suggested that the existence of the dynamically ordered region of water realizing a boson condensation of evanescent photons inside and outside the cell can be regarded as the definition of life.

3T3 Cells↗
PubMed1986

Computer-aided skull/face superimposition.

By use of a special optical device coupled with a TV camera to match a skull and a photograph of a face, superimposition for the purpose of personal identification was performed in controlled situations. A computer-aided method to evaluate the fit of the superimposition has been outlined by means of an original Shape Analytical Morphometry (SAM) software package yielding analytical descriptions by kth-order poly-nominal equations and Fourier harmonic analysis. The match was carried out by using point-cross error and sum of differences for the Fourier set amplitude. A final comprehensive evaluation exhibited marked differences between congruent and noncongruent superimpositions.

Face↗