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At least 217 records · Page 12Linked to original sources
PubMed2000

[A simple method for transposing MRI information to simulation films. Technical note].

BACKGROUND: The use of MRI information in the treatment planning process is still expensive and time consuming. Electro-optical devices or specially designed post-processing software in here the risk of picture distortion. PATIENTS AND METHODS: Between June 1998 and June 1999 in 48 patients with brain tumors and 11 patients with carcinoma of the prostate CT treatment planning and MRI were performed with identical patient positioning using the same devices as in the simulation. The transposition of organ and tumor volumes between MRI and simulation film takes place by overlying both on the brightening screen by using a grid. MRI and simulation films must be produced using an identical magnification factor. RESULTS: For 9 patients with brain tumors and 2 patients with a carcinoma of the prostate the transposition of MRI information on the simulation films showed the necessity of a modification of the shielding or the treatment portals. CONCLUSIONS: The simple method of direct transposition of MRI structures into simulation films allows to accomplish a verification of the portals and conformation which result of the treatment planning process. Moreover an individualized shielding can also directly be realized.

Brain Neoplasms↗
PubMed1987

Measurement of sarcomere shortening in skinned fibers from frog muscle by white light diffraction.

A new optical-electronic method has been developed to detect striation spacing of single muscle fibers. The technique avoids Bragg-angle and interference-fringe effects associated with laser light diffraction by using polychromatic (white) light. The light is diffracted once by an acousto-optical device and then diffracted again by the muscle fiber. The double diffraction reverses the chromatic dispersion normally obtained with polychromatic light. In frog skinned muscle fibers, active and passive sarcomere shortening were smooth when observed by white light diffraction, whereas steps and pauses occurred in the striation spacing signals obtained with laser illumination. During active contractions skinned fibers shortened at high rates (3-5 microns/s per half sarcomere, 0-5 degrees C) at loads below 5% of isometric tension. Compression of the myofibrillar lateral filament spacing using osmotic agents reduced the shortening velocity at low loads. A hypothesis is presented that high shortening velocities are observed with skinned muscle fibers because the cross-bridges cannot support compressive loads when the filament lattice is swollen.

Animals↗
PubMed1990

Histopathologic validation of Fourier-ellipsometry measurements of retinal nerve fiber layer thickness.

We describe a new technique for the measurement of retinal nerve fiber layer thickness and compare its results with histopathologic measurements in the same eyes. For these studies, two fixed monkey eyes were incised and placed on a pedestal in a plastic viewing dish. The eyes were perfused to maintain a pressure between 10 and 20 mm Hg. An ellipsometer, an optical device used to measure the change in polarization of light (retardation), was implemented in a laser tomographic scanner to obtain polarization data from the two monkey retinas. For the 15 measured locations, retardation ranged between a mean (+/- SD) of 0.9 degrees +/- 1.8 degrees and 23.7 degrees +/- 0.3 degrees. Subsequently, retinal nerve fiber layer thickness was measured at the imaged points in epoxy resin-embedded sections by an observer masked to the ellipsometry data. These values ranged between 20.4 microns and 213.9 microns. There was an excellent correlation (R = .83) between retardation and the histopathologic measurement of retinal nerve fiber layer thickness. Quantitating retinal nerve fiber layer thickness may enhance discrimination between glaucomatous and normal eyes earlier than is currently available by anatomic and functional approaches.

Animals↗
PubMed1989

Ocular fluorometry: principles, fluorophores, instrumentation, and clinical applications.

Ocular fluorometry is rapidly evolving as a versatile technique for research and diagnosis in ophthalmology. The main reasons for this increasing success are 1) the ideal characteristics of the eye as an optical device for excitation of tissue fluorescence and for the detection of the fluorescent emission; 2) the development of novel fluorometric techniques, including differential and time-resolved fluorescence spectroscopy; and 3) the increasing use of coupling geometries with high-resolution and high spatial selectivity. Both endogenous and exogenous fluorophores are of interest to ocular fluorometry. The most significant among endogenous fluorophores are the fluorescing pigments of the lens and of the retinal pigment epithelium (RPE). The nature, topography, and fluorescence properties of such pigments depend on age and pathology and on the level of light exposure. Exogenous fluorophores of interest are both intentionally induced and unintentionally accumulated drugs (some of which are phototoxic). Laser-based fluorometric techniques play a leading role in ocular fluorometry. The peculiar properties of the laser for the excitation of fluorescence make this source a favorite candidate for ocular fluorometry both in vitro and in vivo.

Eye Diseases↗
PubMed1995

Scanning laser polarimetry to measure the nerve fiber layer of normal and glaucomatous eyes.

PURPOSE: To determine whether retardation (change in polarization) measurements of healthy subjects and glaucoma patients obtained by using a confocal scanning laser polarimeter correspond to known properties of the nerve fiber layer. METHODS: A polarimeter, an optical device used to measure the change in linear polarization of light (retardation), was interfaced with a scanning laser ophthalmoscope to obtain retardation data at 65,536 locations (256 x 256 pixels) in a study of normal subjects and patients with primary open-angle glaucoma. To validate the instrument, we compared our measurements with known properties of the human retinal nerve fiber layer in 105 normal subjects. Additionally, we compared retardation measurements in eyes of 64 normal subjects and 64 age-matched glaucoma patients treated in a referral practice. RESULTS: In normal eyes, mean (+/- S.D.) peripapillary retardation was highest in the superior and inferior arcuate regions and lowest in the temporal and nasal regions, 12.0 +/- 1.9, 13.1 +/- 2.0, 7.0 +/- 1.8, and 7.0 +/- 1.6 degrees, respectively. Retardation decreased toward the periphery and was lower over blood vessels. In normal eyes, retardation decreased with increasing age in the superior and inferior regions. Mean retardation was statistically significantly higher among normal eyes than glaucoma eyes in the inferior and superior regions but not in the temporal or nasal areas. CONCLUSIONS: Scanning laser polarimetry provides quantitative measurements that correspond to known properties of the retinal nerve fiber layer in normal and glaucomatous eyes.

Adolescent↗
PubMed2004

[Complications after endonasal surgery of the paranasal sinuses for inflammatory diseases].

BACKGROUND: There are sufficient reports on the incidence of complications after endonasal surgery of the paranasal sinuses. It is the aim of this study to calculate the incidence of typical complications after primary and revision surgery, after "functional" and "extended" operations, together with the influence of expertise and of different optical devices on the complications rate. Preoperative computer tomography of the paranasal sinuses are the golden standard. There exists a historical interest to compare the complication rate in patients operated without and those with a CT, especially in those countries where the availability of CTs is low or not existent. METHODS: 266 consecutive patients who underwent an endonasal surgery of the paranasal sinuses from January 1989 to December 1990 were revised to study the incidence and relative risk rate of typical complications after primary and revision surgery, after "functional" or "extended" surgery, the rate for more experienced or less experienced surgeons, as well as the differences between endoscopic or microscopic surgery. The study also compares the complication rate of patients operated on with and without a preoperative computed tomography. RESULTS: 207 out of 263 patients (78.7 %) had no complication. 58 minor and three severe complication were registered for 56 patients. 6 patients had two or more minor complications. No surgeon showed a higher complication rate compared to others (p = 0.33), and there was no statistically significant difference (p = 0.279) in the complication rate between experienced and less experienced surgeons. Endoscopic or microscopic surgery showed no statistically significant differences (p = 0.117) and extended sinus surgery displayed more complications compared to minor surgery (p = 0.041), as well as primary surgery compared to revision surgery (p = 0.003). No statistically significant differences could be found for surgeries performed with or without computed tomography (p = 0.097). CONCLUSIONS: A higher complication rate is to be expected for primary surgery and after extended sinus surgery, especially when an infundibulotomy was performed. In our series no learning curve was observed, especially as the variable "experience" showed no statistically significant difference. Endonasal surgery without CAT scan is not recommended, however, no higher complication rate was found in surgery without CAT scan.

Adolescent↗
PubMed2003

Colloidal crystal films: advances in universality and perfection.

For three-dimensional photonic crystals, made either by top-down microfabrication or by bottom-up self-assembly approaches, to comply with the stringent requirements of optical telecommunication applications, their degree of structural perfection and optical quality must meet an exceptionally high standard. Only with such superior quality photonic crystals can their unique optical properties be harnessed in optical devices and circuits constructed from micrometer-sized optical components. In this paper, we present a new strategy for making silica colloidal crystal films with a sufficiently high level of structural perfection and optical quality to make it competitive as a practical route to photonic crystal optical components. The attainment of this goal takes due cognizance of three key synergistic factors in the film formation process. The first recognizes the necessity to prepare high-quality silica spheres, which are highly monodisperse, with a polydispersity index significantly better than 2%, and the second recognizes that the population of spheres must be devoid of even the smallest fraction of substantially smaller or larger spheres or sphere doublets. The latter turns out to have a minimal effect on the polydispersity index, and yet a major detrimental effect on the overall structural order of the film. The third concerns the film-forming method itself, which necessitated the development of a novel process founded upon isothermal heating evaporation-induced self-assembly (IHEISA) of spheres on a planar substrate. This new method has several advantages over previously reported ones. It is able to deposit very high-quality silica colloidal crystal film rapidly over large areas, with a controlled thickness and without any restrictions on sphere sizes.

Journal Article↗
PubMed2004

Non-invasive monitoring of gingival crevicular fluid for estimation of blood glucose level.

Development of a non-invasive method for measuring the blood glucose level is an urgent necessity, and putting such a method into practical use will enable some of the physical and mental stress that patients with diabetes have to endure to be removed. To realise a non-invasive blood glucose monitor, the gingival crevicular fluid (GCF) was measured. A GCF-collecting device was developed that was designed to be disposable, biocompatible and small enough to be inserted in the gingival crevice for collection of a sub-microlitre sample of GCF. Also, a high-sensitivity glucose testing tape incorporated in the device was developed. Red laser light in a portable optical device measured the colour density of the testing tape. Standard glucose solutions were used to investigate the measurement accuracy of the GCF glucose monitor and showed a correlation coefficient of R = 0.99 (n = 20) between the optical density and the glucose levels. The GCF glucose monitor was evaluated on healthy Swedish and Japanese adults (n = 10) and both GCF glucose levels (GCFLs) and blood glucose levels (BGLs) were measured in conjunction with meal loads. The GCFLs were about 1/10-1/560 lower than the BGLs. No difference in the range of GCFLs between the Swedish and the Japanese subjects was observed. Therefore it was concluded that physique, body mass index and life-style, such as dietary habit, did not significantly influence the GCFLs. Further, the correlation coefficients of all the subjects were 0.70 and 0.88 with each group. It was suggested that GCF could be used as a method of non-invasive blood glucose measurement.

Adult↗
PubMed2002

On-line fourier transform infrared detection in capillary electrophoresis.

The coupling of Fourier transform infrared (FT-IR) spectroscopy as a new on-line detection principle in capillary electrophoresis (CE) is presented. To overcome the problem of total IR absorption by the fused-silica capillaries that are normally employed in CE separations, a micromachined IR-transparent flow cell was constructed. The cell consists of two IR-transparent CaF2 plates separated by a polymer coating and a titanium layer producing an IR detection window, 150 microm wide and 2 mm long, with a path length of 15 microm. The IR beam was focused on the detection window using an off-axis parabolic mirror in an optical device (made in-house) attached to an external optical port of the spectrometer. The connections between the fused-silica capillaries and the flow cell were made by a small O-ring of UV-curing epoxy adhesive on the sharply cut ends of the capillaries, allowing the capillaries to be easily replaced. Aqueous solutions comprising mixtures of adenosine, guanosine, and adenosine monophosphate were used to test the system's performance. Conventional on-line UV detection was employed to obtain reference measurements of analytes after the IR detection flow cell. The limit of FT-IR detection for all analytes (in absolute amounts) was in the nano- to picogram range corresponding to concentrations in the low-millimolar range.

Adenosine↗
PubMed2003

Stochastic resonance in the presence of spatially localized structures.

Stable spatially localized structures exist in a wide variety of spatially extended nonlinear systems, including nonlinear optical devices. We study stochastic resonance (SR) in models of optical parametric oscillators in the presence of a spatially uniform time-periodic driving and in a regime where two equivalent states with equal intensity but opposite phase exist. Diffraction and nonlinearity enable the existence of localized states, formed by the locking of kinks and antikinks and displaying spatially damped oscillatory tails (in one dimension) or the stabilization of dark ring cavity solitons (in two dimensions). We show that SR is inhibited at low driving amplitudes by the presence of localized states which obstruct the front motion. For larger driving amplitudes, in the regime where localized states cease to be stable, we observe instead an enhancement of SR.

Journal Article↗
PubMedDate not supplied

Calibration standards for multicenter clinical trials of fluorescence spectroscopy for in vivo diagnosis.

In the context of clinical trials, calibration protocols for optical instruments that ensure measurement accuracy and the ability to carry out meaningful comparisons of data acquired from multiple instruments are required. A series of calibration standards and procedures are presented to assess technical feasibility of optical devices for cervical precancer detection. Measurements of positive and negative standards, and tissue are made with two generations of research grade spectrometers. Calibration accuracy, ability of standards to correct and account for changes in experimental conditions, and device components are analyzed. The relative frequency of measured calibration standards is investigated retrospectively using statistical analysis of trends in instrument performance. Fluorescence measurements of standards and tissue made with completely different spectrometers show good agreement in intensity and lineshape. Frequency of wavelength calibration standards is increased to every 2 h to compensate for thermal drifts in grating mount. Variations in illumination energy detected between standards and patient measurements require probe redesign to allow for simultaneous acquisition of illumination power with every patient measurement. The use of frequent and well-characterized standards enables meaningful comparison of data from multiple devices and unambiguous interpretation of experiments among the biomedical optics community.

Calibration↗
PubMed2005

A SU-8/PDMS hybrid microfluidic device with integrated optical fibers for online monitoring of lactate.

A microfluidic device with integrated optical fibres was developed for online monitoring of lactate. The device consists of a SU-8 waveguide, microfluidic channels and grooves for the insertion of optic fibres. It was fabricated by one-step photolithography of SU-8 polymer resist. Different channel widths (50-300 microm) were tested in terms of detection sensitivity. A wide range of flow rates were applied to investigate the influence of flow rate on signal fluctuations. The separation between optical fibre sensor and microfluidic channel and the width of fluidic channel have been optimized to maximize the detection sensitivity. It was revealed that 250 microm of channel width is the optimum light path length for a compromise between detection sensitivity and interference of ambient light. The independence of detection signals on flow rates was demonstrated within the range of flow rate (0.5-5 ml/hr) tested. Compared with conventional lactate detection, the device is proved to have high accuracy, relatively low limit of detection (50 mg/L) and reasonably fast response time (100 sec). The fabrication of device is simple and low cost. The present work has provided some fundamental data for further system optimization to meet specific detection requirements.

Biosensing Techniques↗
PubMed2005

Visualization of individual single-walled carbon nanotubes by fluorescent polymer wrapping.

Manipulating optical properties of single-walled nanotubes (SWNTs) is necessary for the development of nanoscale optical devices and probes for biomedical research. In life sciences it will make possible the direct observation of SWNTs inside living cells using optical microscopes. In the nanotechnology field it will enable the development of nanosensors with fluorescent reporting. However, the direct fluorescent labeling of SWNTs is obstructed by their strong light quenching qualities. Besides, chemical functionalization of SWNTs needed for the covalent attachment of fluorescent dyes could change favorable properties of nanotubes. Here we report that optical properties of SWNTs can be manipulated without their covalent modification by wrapping them with fluorescently labeled polymer poly(vinylpyrrolidone) (PVP-1300). Fluorescent PVP-1300 forms a monomolecular approximately 2.5 nm thick layer coiling around individual SWNTs and nanotube bundles. PVP casing is fluorescent although it is only several nanometers thick. This makes individual SWNTs observable by a fluorescent microscope. The spare polymer strands left over after wrapping around the relatively shorter nanotubes form junctions between SWNTs tying them together into new configurations, primarily Y- and psi-type junctions. The ability to use a single fluorescent polymer strand to fasten nanotubes together can be useful in assembly of nanotube-made devices. In PVP-covered SWNTs multiple fluorophores are attached to each single nanotube making them unique composite fluorophores attractive as parts of biological fluorescent probes and in the development of the new materials in photonics and nanotechnology.

Image Enhancement↗
PubMed2004

Superresolution in compensated telescopes.

We present a procedure for attaining resolution beyond the diffraction limit in ground-based telescopes. This procedure is based on the use of rotationally symmetric pupil plane filters that can be easily implemented in dynamic optical devices such as a deformable mirror of an adaptive-optics system. We show that a successful application of the technique requires partial compensation for atmospheric distortion by adaptive optics. Consequently, we derive the required level of compensation as a function of the atmospheric conditions. Finally, our results are checked using simulated data.

Journal Article↗
PubMed1998

On the evolution of some endoscopic light delivery systems for photodynamic therapy.

Progress in photodynamic therapy (PDT) depends on the development of: (1) photosensitizers, (2) optical devices among which are lasers and light delivery systems, and (3) clinical procedure. The light delivery systems which are the focus of this article are fiberoptic devices developed in Lausanne, Switzerland for use in the endoscopic treatment of cancer or precancerous lesions in the bronchi, the esophagus, the uterus, the cervix, the upper aerodigestive tract and thoracic cavity. Light delivery systems for both surface and interstitial application are presented, together with some of the physical principles on which they are based. Incorporation in these devices of the possibility for in-situ measurement of reflected therapeutic light and/or fluorescence emitted by endogenous and/or exogenous dyes allows for improved light and drug dosimetry, as well as the measurement of photobleaching, local oxygenation and other tissue properties. The necessity of information on tissue optical parameters, as well as the use of simple mathematical models and tissue phantoms, for optimizing light distributing devices is underlined. The devices are optimized for delivering the desired light intensity distribution to the targeted region with minimal losses. In some cases this implies using the device to modify the shape of the hollow organ during PDT, an example of which is given for the case of the esophagus. In another strategy, one adapts the shape of the device to that of the organ, using an elastic balloon catheter. Here examples are given for the uterus, the bronchi and the thoracic cavity. The mechanical properties, the sizes, shapes and materials of the light delivery systems must be optimized for safe use while retaining low cost. Furthermore, the devices must whenever possible be rendered compatible with existing medical technology. A significant improvement in clinical efficacy has been demonstrated in the testing of some of these new fiberoptic light delivery systems. For endoscopic PDT in the hollow organs, the design and optimalization of multiple new approaches to light distribution will continue to lead to improved clinical results.

Bronchial Neoplasms↗
PubMed2005

Effects of interchanging hyperopic defocus and form deprivation stimuli in normal and optic nerve-sectioned chicks.

To test the hypothesis that the same mechanisms mediate form deprivation and lens-induced myopia, the ocular growth responses of chicks alternately exposed to lenses and diffusers at regular intervals (3h) were compared to those of chicks exposed to either negative lenses or diffusers alone. In total, there were four experiments: (1) -15 D lenses and/or diffusers on normal birds, (2) -15 D lenses and/or diffusers on optic nerve-sectioned (ONS) birds, (3) -5/-10/-15 D lenses (sequentially applied) and/or diffusers on normal birds and (4) -5/-10/-15 D lenses and/or diffusers on ONS birds. All treatments were monocular. In all experiments, optical axial lengths (cornea-to-retina distances) in treated eyes were greater than in fellow eyes, irrespective of the optical device (diffuser, lens or switch), lens power (fixed or incremented) and optic nerve condition (intact or severed). In normal chicks, optical axial length responses in the switch group were significantly reduced relative to those of the diffuser but not to those of the -15 D lens group. For both groups of ONS birds, diffusers exaggerated the optical axial length changes. For all groups, the responses to the switch and lens groups were most similar. These results together suggest that the mechanisms mediating form deprivation- and lens-induced myopia are different.

Animals↗
PubMed2006

Experimental demonstration of continuous variable purification of squeezed States.

We report on the first experimental demonstration of purification of nonclassical continuous variable states. The protocol uses two copies of phase-diffused states overlapped on a beam splitter and provides Gaussified, less mixed states with the degree of squeezing improved. The protocol uses only linear optical devices such as beam splitters and homodyne detection, thereby proving these optical elements can be used for successful purification of this type of state decoherence which occurs in optical transmission channels.

Journal Article↗
PubMed2006

Demonstration of a nanoparticle-based optical diode.

We present the operation of an optical device that exhibits diodelike properties based on two adjacent layers of quantum dots (QDs) encased in a fiber-optic jacket. The possibility of a multilayered device is also discussed. A significant change in the emission spectrum of CdSe/ZnS core-shell QDs was observed when excited by the input laser and the fluorescence of other CdSe/ZnS core-shell QDs. The output of the diode can be taken to be either the incoming laser wavelength of light similar to a conventional diode, or the output may be considered to be one of the QD fluorescence wavelengths. Current work has applications in biological fluorescence monitors and sensors as well as in telecommunications applications.

Journal Article↗