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At least 1,549 records · Page 86Linked to original sources
PubMed1999

Clinical use of the optical digitizer for intracranial neuronavigation.

OBJECTIVE: Computer-assisted frameless navigation techniques are used in many centers for intracranial neurosurgical procedures. In this study, we assessed the accuracy and the clinical usefulness of a frameless system based on the optical digitizer in a variety of intracranial procedures. METHODS: The optical digitizer (StealthStation, Sofamor Danek, Memphis, TN) was used to perform 170 neurosurgical operations. Its accuracy was judged before and after each operation by comparing the computer-estimated error with the real estimated error measured on the patient's anatomy. Several objective factors were evaluated to assess the clinical usefulness of the optical digitizer. For craniotomies, the intraoperative extent of resection based on computer-generated images was compared with that on postoperative images, and the length of hospital stay of patients undergoing frameless procedures was compared with that of patients undergoing conventional procedures. For needle biopsies, clinical usefulness was based on the rate of success in establishing a histological diagnosis. RESULTS: The optical digitizer was accurate to within 2 mm for all procedures. The computer-estimated error was not significantly different from the real estimated error. The intraoperative extent of resection was accurate in 58 of 60 tumor resection patients, as confirmed on postoperative images. Patients undergoing frameless procedures had a significantly shorter hospital stay than those undergoing conventional procedures (7.5 +/- 1 versus 10.8 +/- 1.3 d, P < 0.05). All biopsies were diagnostic. CONCLUSION: The optical digitizer is an accurate frameless device that offers clinical benefits. These include precise surgical resection, decreased hospitalization time, and accurate tissue diagnosis.

Adolescent↗
PubMed1991

A programmable data acquisition and control system for magnetic resonance imaging: application to mutually coupled surface coil arrays and temperature monitoring.

A programmable data acquisition and control system was developed for use in conjunction with magnetic resonance imaging (MRI). The controller consists of two functional blocks: a host system and a remote system. The remote system resides inside the shielded room housing the magnet. The host, an IBM compatible personal computer, is located at the technician's console. Communication between these devices is implemented over a fiber optic RS-232 data link. This configuration allows experiments to be performed remotely by using a series of keyboard typed commands, by programming the host to send a series of commands, or by directly programming the remote system. As an example of its capabilities, the controller was used to tune and match arrays of receiver coils for localized imaging and to record the rectal temperature of a sedated rat during image acquisition.

Algorithms↗
PubMedDate not supplied

A real time optoelectronic device as an adjunct to the Pap smear for cervical screening: a multicenter evaluation.

We report on the results from a multicenter trial for a real time optoelectronic device as an adjunct to the Pap smear for cervical screening. TruScreen (Polartechnics Limited, Sydney, Australia) is an automated device which measures the response to optical and electrical stimulation of the cervix and returns a screening result in real time. Analysis was performed on a group of 651 subjects recruited at 10 centers. Cytology and histology analyses were performed by centralized laboratories, with the cytology classification performed according to the Bethesda 2001 system. The sensitivities for histologically confirmed CIN 2/3 lesions by TruScreen, Pap, and TruScreen/Pap combined were 70% (95% CI: 67-74), 69% (CI: 65-72), and 93% (CI: 91-95), respectively. For histologically reported CIN 1, the sensitivities of the TruScreen, Pap, and combined test were 67% (CI: 63-70), 45% (CI: 41-49), and 87% (CI: 84-89). The improvement in sensitivity for the combined test compared to the Pap smear alone was significant (P = 0.002). Because TruScreen and cytology detect partly different but overlapping groups of CIN cases, the adjunctive combination provides very high CIN detection rates.

Adult↗
PubMed1997

Age-related changes in facial skin contours and rheology.

OBJECTIVES: To evaluate the age effect on both the mechanical properties and wrinkling of facial skin. This topic has not previously been addressed in the literature. DESIGN: A total of 180 white women aged 18 to 67 years participated in the study. Each of the 5 decades of age was represented by 30 subjects, with the exception of menopausal women aged 48 to 57 years who were allocated to two groups of 30 according to the use or non-use of hormone replacement therapy (HRT). SETTING: A University medical center, Belgian SSTC Research Unit 5596. MEASUREMENTS: Mechanical properties of the skin were measured on the face using a computerized suction device. Skin contours were assessed using optical profilometry and computerized image analysis. RESULTS: Skin aging of the face is characterized by a progressive increase in extensibility associated with a decreased elasticity. The loss of tonicity is accompanied by a progressive deepening of facial creases. HRT appears to limit the age-related rheological changes without showing a preventive effect on wrinkling of facial skin. CONCLUSION: Aging of facial skin resembles, in some ways, the features previously reported on sun-protected areas of the forearms. HRT has a beneficial effect that may slow the overall process of aging without, however, limiting the number and depth of wrinkles.

Adolescent↗
PubMed2005

The nanopore connection to cell membrane unitary permeability.

Artificial nanopores have recently emerged as versatile tools for analyzing and sorting single molecules at high speed. However, the biological cell has already developed a large set of sophisticated protein nanopores that are able to selectively translocate all types of molecules through membranes. Therefore, hybrid devices combining artifical solid-state with biomimetic protein nanopores appear to us as a particularly promising approach to the creation of powerful diagnostic, preparative and therapeutic devices. Here, we discuss a technique, optical single-transporter recording (OSTR), in which arrays of artificial micropores and nanopores are employed to analyze protein nanopores of cellular membranes. After briefly summarizing some salient features of OSTR, the technique is compared with the electrical patch clamp method and the first results of our efforts to amalgamate optical and electrical recording are described. Finally, prospects for combining OSTR with 4Pi microscopy, single-molecule fluorescence spectroscopy and fluorescence correlation spectroscopy are discussed.

Biomimetic Materials↗
PubMed2006

Development and characterization of a tissue equivalent plastic scintillator based dosimetry system.

High precision techniques in radiation therapy, such as intensity modulated radiation therapy, offer the potential for improved target coverage and increased normal tissue sparing compared with conformal radiotherapy. The complex fluence maps used in many of these techniques, however, often lead to more challenging quality assurance with dose verification being labor-intensive and time consuming. A prototype dose verification system has been developed using a tissue equivalent plastic scintillator that provides easy-to-acquire, rapid, digital dose measurements in a plane perpendicular to the beam. The system consists of a water-filled Lucite phantom with a scintillator screen built into the top surface. The phantom contains a silver coated plastic mirror to reflect scintillation light towards a viewing window where it is captured using a charge coupled device camera and a personal computer. Optical photon spread is removed using a microlouvre optical collimator and by deconvolving a glare kernel from the raw images. A characterization of the system was performed that included measurements of linear output response, dose rate dependence, spatial linearity, effective pixel size, signal uniformity and both short- and long-term reproducibility. The average pixel intensity for static, regular shaped fields between 3 cm X 3 cm and 12 cm x 12 cm imaged with the system was found to be linear in the dose delivered with linear regression analysis yielding a correlation coefficient r2 > 0.99. Effective pixel size was determined to be 0.53 mm/pixel. The system was found to have a signal uniformity of 5.6% and a long-term reproducibility/stability of 1.7% over a 6 month period. The system's ability to verify a dynamic treatment field was evaluated using 60 degrees dynamic wedged fields and comparing the results to two-dimensional film dosimetry. Results indicate agreement with two-dimensional film dosimetry distributions within 8% inside the field edges. With further development, this system promises to provide a fast, directly digital, and tissue equivalent alternative to current dose verification systems.

Biomimetic Materials↗
PubMedDate not supplied

An electronic device for digitizing radiotherapy films for the construction of tissue compensators.

An electronic device was designed that measures film optical density and may be attached to the sonic pen of an x,y graphics terminal. Therapy portal films may be digitized by moving the assembly across the film by hand. Data is measured at a rate of 40 data points per second; hence, a large film can be digitized in about 5 min. Supporting computer software constructs a matrix array of optical densities covering the area of the film, converts optical density to dose, and plots tissue compensators. The concept of designing compensators from port films is reviewed. Phantom studies were performed to show that the compensators so designed are satisfactory for clinical application.

Models, Structural↗
PubMed2002

Analysis of piezoelectric strip waveguides based on the effective index and pseudospectral element methods.

Integrated acousto-optical circuits in LiNbO3 are attractive devices for applications especially in advanced WDM systems. In order to increase the scale of integration and to reduce the RF driving power of these devices, one promising approach is to use acoustical waveguides with smaller lateral dimensions. In this paper the combination of a pseudospectral elements method (PSEM) and an effective index method (EIM) for the analysis of film-loaded surface acoustic waveguides (SAWG's) is presented. Numerical results demonstrate the exponential rate of convergence of the PSEM and agree with the computations performed via the transverse resonance technique. Due to the exponential rate of convergence of the PSEM and to a mapping transformation in the substrate, the piezoelectric problem in the depth direction of the structures is evaluated by a low number of Legendre polynomials. The method is applied to the analysis of several layered SAWG's of practical interest for AO devices, such as metal/SiO2/X - YLiNbO3, in which the metal is either Au, Al, In, or Ti.

Journal Article↗
PubMed2003

Reproducibility of ophthalmodynamometric measurements of central retinal artery and vein collapse pressure.

BACKGROUND: To assess the reproducibility of ophthalmodynamometric measurements using a new, Goldmann contact lens associated, device allowing biomicroscopic visualisation of the optic disc. METHODS: The prospective clinical study included 87 eyes of 58 subjects presenting with a normal fundus (n=40), or ocular diseases (n=47). With topical anaesthesia, a Goldmann contact lens, fitted with a pressure sensor mounted into the holding ring of the contact lens, was placed onto the cornea. Pressure was applied onto the globe through the contact lens, and the pressure values obtained when the central retinal vessels started pulsating were noted. The measurements were performed 10 times. RESULTS: The mean coefficients of variation for redeterminations of the collapse pressure of the central retinal vein and artery were 16.3% (SD 11.4%), and 8.5% (4.1%), respectively. CONCLUSIONS: A simple and new, Goldmann contact lens associated, ophthalmodynamometer allows central retinal artery and vein collapse pressure measurements which are reproducible in a clinical setting.

Adult↗
PubMed2004

Synthesis and unusual electron paramagnetic resonance spectrum of metastable nanoclusters of ZnO semiconductor crystallites.

Metastable nanoclusters of ZnO semiconductor crystallites, 20 to 30 nm diameter, are synthesized by a reconstructive decomposition of a polymer precursor of dispersed Zn2+ cations in poly vinyl alcohol (PVA) polymer molecules. They have EPR (electron paramagnetic resonance) spectrum of distinct excitonic features. Multiple EPR bands appear in prominent intensities in oxygen vacancies VO+ and singly ionized Oi- and Zn(i)+ interstitials. A paramagnetic VO+ vacancy derives from usual diamagnetic O2- vacancy of VO++ (behaves as if doubly charged compared to the lattice) by addition of one electron. The results demonstrate the existence of a surface-interface or surface barrier layer in free-carrier depletion at the crystallite surface in the clusters and its effects on the Oi- and Zn(i)+ ionization states (determine green photoluminescence). Both VO+ and Zn(i)+ are curable by a thermal annealing in O2 gas. A cured sample of equilibrium structure achieved by heating at approximately 550 degrees C has a single EPR in Oi- at g = 1.990. The results are useful in understanding their correlation with EPR and optical properties in ZnO semiconductors and devices.

Crystallization↗
PubMed2003

Is Devic's neuromyelitis optica a separate disease? A comparative study with multiple sclerosis.

Devic's neuromyelitis optica (NMO) associates optic neuritis and myelopathy without other neurological signs. Many patients with NMO may be diagnosed as having multiple sclerosis (MS). However, there have been no previous studies comparing these two pathologies and it is still unclear if NMO is a separate entity or a subtype of MS. In the present study, we compared a series of NMO patients with a series of MS patients for whom optic neuritis or myelopathy was the presenting symptom, in order to determine the place of NMO in the spectrum of MS. We retrospectively studied 30 patients diagnosed with NMO and we compared these patients with 50 consecutive MS cases revealed by optic neuritis or acute myelopathy. MS patients were only included if a relapse occurred demonstrating time and space dissemination. We compared the two groups in terms of clinical presentation, laboratory findings (MRI and CSF) and clinical outcome. NMO patients were older and more frequently women than MS patients but the difference was not significant. CSF and MRI data were clearly different: oligoclonal bands (OCB) were found in 23% of NMO cases and 88% of MS (P < 0.001), abnormal brain MRI data were observed in 10% of NMO cases and 66% of MS (P < 0.001) and a large spinal cord lesion was observed in 67% of NMO cases and 7.4% of MS cases (P < 0.001). Clinical outcome was evaluated as more severe in the NMO group (P < 0.001). On the basis of clinical data, all NMO patients but three had dissemination in time and space. When we included MRI parameters, only two of the NMO patients met criteria for MS and one of the MS patients met criteria for NMO. Our study demonstrates that NMO and MS should be considered as two different entities. The respective criteria for NMO and MS were able to distinguish these two pathologies but only when MRI data were applied. This finding could have implications for future therapeutic trials.

Adult↗
PubMed2003

Optimized design of fluorinated polyimide based interleaver.

Statistical optimization method for the design of a fluorinated polyimide wavelength division element for optical communication is proposed. The opitimized device is an interleaver element suitable for dividing over 40 wavelengths in the 1550 nm band. Optimization considers the inherent polarization dependence of fluorinated polyimide based on measurements of the dispersion characteristics and birefringence of fluorinated polyimide film. A 40-wavelength device is designed by use of the proposed technique for a working wavelength of 1550 nm and a wavelength interval of 0.8 nm. The device exhibited a 1-dB passband of 0.5 nm and a 3-dB passband of 0.8 nm, and output wavelength fluctuation due to polarization effects of less than 0.08 nm.

Journal Article↗
PubMed2005

Corrections of size-of-source effect and distance effect in radiometric measurements of radiance.

Many optical instruments used in quality control of the optical radiation emission level of several devices are limited by the so-called size-of-source effect (SSE) as well as the distance effect (DE) when we are dealing with very accurate measurements. Different authors have studied the SSE and DE and have proposed experimental methods that provide corrections for them. We describe a general method based on the partial coherence theory that allows us to describe and calculate the SSE and DE in any radiometric system with circular apertures. We show some experimental results that verify our proposal. Additionally, as a practical example, we present the corresponding DE and SSE correction factors for a particular geometry.

Journal Article↗
PubMed2005

Creation of line defects in holographic photonic crystals by a double-exposure thresholding method.

Recording of periodic variations of amplitude and phase by the interference of coherent laser beams in a hologram offers a natural means for creating one-, two-, and three-dimensional photonic crystals. For device applications such as waveguides in optical communications, one usually needs to create defects in photonic crystals. We present an analysis and an experimental demonstration of a double-exposure method for creating photonic crystals with line defects. The idea is based on the principle of superposition of holographic grating patterns of different spatial periods while the recording medium is held stationary and on the application of a threshold to the recording medium. We use the same symmetrical optical architecture to achieve nondefective and defective holographic photonic crystals. The technique may be extended to the creation of defects based on functional synthesis by means of Fourier series, by use of light sources of other wavelengths with an appropriate high-contrast recording material.

Journal Article↗
PubMed2006

Focusing concave lens using photonic crystals with magnetic materials.

The guided modes lying in the upper gap-edge band in the photonic band structure of photonic crystals have negative values of refractive index. This feature generates many interesting optical phenomena, and some spectacular photonic devices such as focusing slabs have been developed. We report the design of a photonic-crystal, planoconcave lens for focusing incident parallel light, and theoretically analyze the chromatic aberrations for TM and TE modes. In addition to dielectric photonic crystals, the chromatic aberration of a magnetic photonic-crystal planoconcave lens was investigated because the magnetic permeability may also contribute to the periodic index contrast in photonic crystals, especially at long wavelengths. A significant difference was found in the chromatic aberration for a TM mode propagating in a dielectric than in a magnetic photonic-crystal planoconcave lens.

Journal Article↗
PubMed2004

Promising compact wavelength-tunable optical add-drop multiplexer in dense wavelength-division multiplexing systems.

We design and model a highly compact and tunable optical add-drop multiplexer (OADM) device that consists of long-period gratings and piezoelectric ceramic fiber stretchers. The proposed OADM shows that 50 dense wavelength-division multiplexing channel signals can be selected in the wavelength range from 1526.25 to 1563.75 nm with 0.75-nm channel spacing, which covers the whole C-band gain spectrum of an erbium-doped fiber amplifier. The cross talk between channels is less than -39 dB, and the total insertion loss of the device is approximately 0.24 dB, which includes the splicing losses, the mode mismatching loss, and the expected losses in the two side-by-side coupled fibers.

Journal Article↗
PubMed2005

D-type fiber biosensor based on surface-plasmon resonance technology and heterodyne interferometry.

A D-type fiber biosensor based on surface-plasmon resonance (SPR) technology and heterodyne interferometry is presented. The sensing device is a single-mode optical fiber in which half the core is polished away and a thin-film layer of gold is deposited. We measure the phase-difference variations instead of the light intensity as in traditional SPR techniques. Therefore the accuracy and resolution of our method are very high. Its sensitivity can reach 2 x 10(-6) refractive-index units. The sensor has some merits, e.g., tunable high sensitivity, small size, lower cost, smaller sample volume, and suitability for in vivo testing. This novel method of a D-type fiber biosensor based on SPR technology and heterodyne interferometry is valuable for chemical, biological, and biochemical sensing, and the novel method of D-type fiber biosensing is a feasible means of study.

Alcohols↗