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At least 1,423 records · Page 79Linked to original sources
PubMed1994

Flash Dent: an alternative charge-coupled device/scintillator-based direct digital intraoral radiographic system.

The Flash Dent digital intraoral radiographic system is yet to be described in the scientific literature. A Windows operating environment, a lens based optical scintillator charge-coupled device (CCD) and 'IMG' image format are the major features which distinguish this from other available systems. In this paper we describe the component of the Flash Dent system, investigate the validity of the X-ray generator specifications, determine comparative image doses and assess the performance of the intraoral sensor. Although we found Flash Dent software facilitates image processing, X-ray generator operation, sensor performance and dimensional measurements, inconsistencies between sensors and the use of a non-standard image format require further consideration for improvements on the part of the manufacturer.

Humans↗
PubMed2002

Microscopic phase-shifting profilometry based on digital micromirror device technology.

A microscopic three-dimensional (3-D) shape measurement system based on digital fringe projection has been developed and experimentally investigated. A Digital Micromirror Device along with its illumination optics is integrated into a stereomicroscope, which projects computer-generated fringe patterns with a sinusoidal intensity profile through the microscope objective onto the object surface being measured. The fringe patterns deformed by the object surface are recorded by a CCD camera. The microscopic 3-D shape of the object surface is measured and reconstructed by use of a phase-shifting technique. We discuss design considerations and error analysis of the system. Experimental results successfully demonstrate the capability of this technique for surface profile measurement of rough surfaces at the micrometer level.

Journal Article↗
PubMed2006

Systematic modeling study of channel waveguide fabrication by thermal silver ion exchange.

A systematic study of thermal silver ion exchange used for the fabrication of optical channel waveguides is reported in a single-alkali glass. The diffusion equilibrium and diffusion dynamics are experimentally studied, and the concentration-dependent diffusion coefficients are determined. The relationship between the fabrication conditions, i.e., time, temperature, and melt concentration, and the induced waveguide refractive index profile is established. It is demonstrated that the diffusion equation can be solved, without use of any free parameters, to predict the refractive index profiles of both planar and channel waveguides. A 1.6 cm diameter integrated optic ring resonator, with a propagation loss of 0.1 dB/cm, is fabricated in a glass by thermal silver ion exchange. The induced refractive index profile is related to the optical characteristics of the functional device.

Journal Article↗
PubMed2006

Electrically injected quantum-dot photonic crystal microcavity light sources.

The design, fabrication, and characterization of an electrically injected quantum-dot photonic crystal microcavity light source are described. The optical gain in the GaAs/AlGaAs-based device is provided by self-organized InGaAs quantum dots with ground-state room-temperature emission at 1.1 microm. The carriers are injected directly into the photonic crystal microcavity, which contains approximately 50 dots, avoiding surface state recombination in the photonic crystal pattern. The spectral characteristics of a single-defect photonic crystal microcavity show a single 2 nm broad microcavity resonance. The output power is of the order of a few tens of nanowatts.

Journal Article↗
PubMed2002

Routine postoperative imaging is important after ureteroscopic stone manipulation.

PURPOSE: Improved fiber optics and advanced intracorporeal lithotripsy devices have significantly decreased the incidence of complications during ureteroscopic procedures. Despite recent reports suggesting that radiographic imaging may not be necessary in all individuals after routine ureteroscopy silent obstruction may develop in some, ultimately resulting in renal damage. We determined the incidence of postoperative silent obstruction at our institution and assessed the need for routine functional radiographic studies after ureteroscopy. MATERIALS AND METHODS: We retrospectively reviewed the charts of 320 patients who underwent a total of 459 ureteroscopic procedures for renal or ureteral calculi in a 3-year period. Complete followup with imaging was available for 241 patients (75%). Average patient age was 47.2 years. The variables of interest reviewed included preoperative pain, preoperative obstruction, targeted calculous site, stone-free rate, postoperative pain and postoperative obstruction. Mean followup was 5.4 months (range 2 to 43). RESULTS: A total of 241 patients with complete followup were identified in this analysis. Preoperative pain was present in 202 patients (84%) and 168 (70%) had preoperative obstruction. Overall targeted calculous clearance was successful in 73% of the patients and an additional 15.8% had residual fragments less than 4 mm. The renal, proximal or mid and distal ureteral stone-free rate was 32.1%, 81.9% and 90.5%, while in an additional 46.4%, 6.3% and 6.7% of cases, respectively, residual fragments were less than 4 mm. Of the 241 patients 30 (12.3%) had obstruction postoperatively due to residual stone in 25 (83.3%), stricture in 3 (10%), edema of the ureteral orifice in 1 (3.3%) and a retained encrusted stent in 1 (3.3%). Postoperatively obstruction correlated with postoperative pain in 23 of the 30 patients (76.7%). Pain was present postoperatively in 30 of the 211 patients (14%) without evidence of ureteral obstruction postoperatively. However, silent obstruction developed in 7 patients (23.3%) or 2.9% of the total cohort. All 7 patients underwent secondary ureteroscopy to alleviate obstruction. A single patient ultimately received chronic hemodialysis for renal failure, 1 was lost to followup and in 5 there was documented successful resolution of the cause of obstruction. CONCLUSIONS: Our analysis suggests that silent obstruction remains a potentially significant complication after stone management. Relying on postoperative pain to determine the necessity of postoperative imaging places patients at risk for progressive renal failure due to unrecognized obstruction. Therefore, we recommend that imaging of the collecting system should be performed by excretory urography, spiral computerized tomography or ultrasound within 3 months after routine ureteroscopic stone treatment to avoid the potential complications of unrecognized ureteral obstruction.

Adult↗
PubMed2005

Experimental comparison between autofluorescence spectra of constrained fresh and cryopreserved arteries.

The study of mechanical properties of the arterial wall is an important step in the comprehension of the vascular physiopathological functioning. However, cryopreserving biological tissues using very low temperatures can induce biological and structural modifications which may involve complications (dilatation, bursting, stenosis) after reimplantation. Many procedures of mechanical tests (traction, dilatation) developed in research allow us to comprehend and analyse rheological behaviour of the arterial wall. The study presented in this article offers a new perspective to detect changes of mechanical properties of cryopreserved arterial samples. In fact, the original idea is to couple a mechanical test bed (uniaxial traction of arterial rings) with spectroscopic measurements (autofluorescence) for the purpose of correlating mechanical modifications and spectral variations. Ultimately, this new approach could lead to develop a device allowing atraumatic and contactless optical examinations of arterial graft to determine its mechanical state before reimplantation.

Animals↗
PubMed1980

Industrial safety glasses -- an update.

A review is presented of recent significant developments in industrial protective eyewear. Many of these developments apply to everyday practice. The new plastic protective, prescription, and plano lenses are discussed, and their merits presented. Needs for protection in the ultraviolet and near-infrared portions of the electromagnetic spectrum are described. It is shown that such spectral protection is now available in plastic lenses, but care must be taken to insure that the plastic has the required ultraviolet and near-infrared absorption. Eye protection standards have been improved. Specific changes in the standards are discussed.

Accidents, Occupational↗
PubMed1996

Laser induced autofluorescence diagnosis of bladder tumors: dependence on the excitation wavelength.

PURPOSE: We assessed the ability of laser induced autofluorescence spectroscopy to distinguish neoplastic urothelial bladder lesions from normal or nonspecific inflammatory mucosa. MATERIALS AND METHODS: Three different pulsed laser excitation wavelengths were used successively: 308 nm. (xenium chloride excimer laser), 337 nm. (nitrogen laser) and 480 nm. (coumarin dye laser). The excitation light was delivered by a specially devised multifiber catheter connected to a 1 mm. core diameter silica monofiber introduced through the working channel of a standard cystoscope with saline irrigation. The captured fluorescence light was focused onto an optical multichannel analyzer detection system. Device performance was evaluated in 25 patients after obtaining consent and immediately before transurethral resection of a bladder tumor. Spectroscopic results were compared with histological findings. RESULTS: At 337 and 480 nm. excitation wavelengths the overall fluorescence intensity of bladder tumors was clearly decreased compared to normal urothelial mucosa regardless of tumor stage and grade. At the 308 nm. excitation wavelength the shape of the tumor spectra, including carcinoma in situ, was markedly different from that of normal or nonspecific inflammatory mucosa. No absolute intensity determinations were required in this situation, since a definite diagnosis could be established based on the fluorescence intensity ratio at 360 and 440 nm. CONCLUSIONS: This spectroscopic study could be particularly useful to design a simplified autofluorescence imaging device for detection of occult urothelial neoplasms.

Carcinoma in Situ↗
PubMed1998

[Biliary reflux can be a contributory cause of esophagitis].

In recent years duodenogastric reflux has been recognised as a possible cause of oesophagitis. Alone or in combination, bile salts, trypsin, pepsin, and hydrochloric acid have all been shown to cause oesophagitis. Duodenal content in the oesophagus can be measured by means of a new fibre-optic sensor, Bilitech 2000, a device measuring the occurrence of bilirubin and yielding 24-hour readings from the distal oesophagus. Studies in which the device has been used have shown oesophageal bilirubin to be increased in patients with oesophagitis, especially in the subgroup with such complications as oesophageal stricture or ulceration, or Barrett's oesophagus. The evidence suggests that unsatisfactory response to proton pump inhibitors in reflux patients might be due to an increase in duodenal reflux, and should be treated surgically with fundoplication or biliary diversion. This may also be true of oesophagitis patients with complications, though this remains to be shown in clinical studies.

Barrett Esophagus↗
PubMed2005

Optical analysis of perfusion bioreactor cell concentration in an acoustic separator.

Automated monitoring of cell concentration in perfusion bioprocesses facilitates the maintenance of constant cell specific perfusion rates. However, most on-line measuring devices are relatively complex and foul as the culture progresses. A simple external optical sensor was developed using the transparent glass walls of acoustic separators for automated optical analysis of their contents. For each measurement, the separator was filled by an automated pumping system with triplicate representative bioreactor samples that were optically analyzed and the device returned to perfusion operation within approximately 1 or 2 min. Chinese hamster ovary cell concentrations, ranging from 5 x 10(5) to 2 x 10(7) cells/mL, were highly correlated (R(2) = 0.99) with the 90 degrees scattered light response. Since the device was operated externally, it did not complicate bioreactor sterilization or cleaning. Viability was not optically analyzed, but this information was not required between manual samples of a properly operated perfusion process. Using single-point recalibration based on routine off-line samples, this external optical system remained effective during a 4-month perfusion run, thus providing a non-invasive and easily maintained on-line cell concentration monitoring system to improve the control of perfusion bioreactors.

Acoustics↗
PubMed2004

Pure-silica optical waveguides, fiber couplers, and high-aspect ratio submicrometer channels for electrokinetic separation devices.

A new fabrication procedure for integration of ultraviolet transparent pure-silica planar waveguides, fiber couplers and high-aspect ratio submicrometer channels is presented. Only a single photolithographic mask step is required. The channels are 80-90 microm deep and the width can be reduced to about 0.5 microm, corresponding to a height-to-width ratio of more than 150. The core of the waveguides consists of pure silicon dioxide, which is favorable over doped silica, due to the absence of absorption centers associated with the dopants. This furthermore improves the long-term stability of the waveguides, because of an increased radiation resistance of the glass. The propagation loss decreases from 1.0 dB/cm at 200 nm to 0.2 dB/cm at 800 nm, which, to our knowledge, is the lowest propagation loss reported for integrated planar waveguides in the ultraviolet wavelength region to date. The effective optical path length is 1.2 mm for an absorbance cell with a nominal length of 1.0 mm, indicating effective suppression of stray light. The limit of detection for paracetamol when present in the entire channel network was determined to 3 microg/mL. Finally, the applicability of the fabricated devices for capillary electrophoresis was evaluated by separation of caffein, paracetamol and ketoprofone using absorbance detection at 254 nm.

Acetaminophen↗
PubMed2003

Hand-held arthroscopic optical coherence tomography for in vivo high-resolution imaging of articular cartilage.

We describe a novel hand-held polarization optical coherence tomographic (OCT) probe that can be inserted into mammalian joints to permit real-time cross-sectional imaging of articular cartilage. The transverse and axial resolutions of the arthroscopic OCT device are roughly 17 and 10 microm, respectively. Two-dimensional cross-sectional images of cartilage tissue with 500 x 1000 pixels covering an area 6 mm in length and 2.8 mm in depth can be acquired at nearly five frames/s and with over 100 dB of dynamic range. Design of an OCT as a hand-held device capable of providing such an optical biopsy of articular cartilage allows eventual in vivo detection of microstructural changes in articular cartilage that are not apparent using conventional arthroscopic cameras. The OCT probe can be easily incorporated in a conventional arthroscope for cartilage site guidance. The optical arrangement in the OCT scope minimizes specular back-reflection of the probe end face and absorption of body fluid in the path and ensures in-focus OCT imaging when it is in contact with the cartilage specimen to be examined. Successful application of in vivo arthroscopy to porcine articular cartilage demonstrates sufficient resolution and practicality for use in human joints.

Animals↗
PubMed1996

Sinusoidal modulation analysis for optical system MTF measurements.

The modulation transfer function (MTF) is a commonly used metric for defining the spatial resolution characteristics of imaging systems. While the MTF is defined in terms of how an imaging system demodulates the amplitude of a sinusoidal input, this approach has not been in general use to measure MTFs in the medical imaging community because producing sinusoidal x-ray patterns is technically difficult. However, for optical systems such as charge coupled devices (CCD), which are rapidly becoming a part of many medical digital imaging systems, the direct measurement of modulation at discrete spatial frequencies using a sinusoidal test pattern is practical. A commercially available optical test pattern containing spatial frequencies ranging from 0.375 cycles/mm to 80 cycles/mm was sued to determine the MRF of a CCD-based optical system. These results were compared with the angulated slit method of Fujita [H. Fujita, D. Tsia, T. Itoh, K. Doi, J. Morishita, K. Ueda, and A. Ohtsuka, "A simple method for determining the modulation transfer function in digital radiography," IEEE Trans. Medical Imaging 11, 34-39 (1992)]. The use of a semiautomated profiled iterated reconstruction technique (PIRT) is introduced, where the shift factor between successive pixel rows (due to angulation) is optimized iteratively by least-squares error analysis rather than by hand measurement of the slit angle. PIRT was used to find the slit angle for the Fujita technique and to find the sine-pattern angle for the sine-pattern technique. Computer simulation of PIRT for the case of the slit image (a line spread function) demonstrated that it produced a more accurate angle determination than "hand" measurement, and there is a significant difference between the errors in the two techniques (Wilcoxon Signed Rank Test, p < 0.001). The sine-pattern method and the Fujita slit method produced comparable MTF curves for the CCD camera evaluated.

Biophysical Phenomena↗
PubMed2004

Nanoribbon waveguides for subwavelength photonics integration.

Although the electrical integration of chemically synthesized nanowires has been achieved with lithography, optical integration, which promises high speeds and greater device versatility, remains unexplored. We describe the properties and functions of individual crystalline oxide nanoribbons that act as subwavelength optical waveguides and assess their applicability as nanoscale photonic elements. The length, flexibility, and strength of these structures enable their manipulation on surfaces, including the optical linking of nanoribbon waveguides and other nanowire elements to form networks and device components. We demonstrate the assembly of ribbon waveguides with nanowire light sources and detectors as a first step toward building nanowire photonic circuitry.

Journal Article↗
PubMed2005

A fully automated calibration method for an optical see-through head-mounted operating microscope with variable zoom and focus.

Ever since the development of the first applications in image-guided therapy (IGT), the use of head-mounted displays (HMDs) was considered an important extension of existing IGT technologies. Several approaches to utilizing HMDs and modified medical devices for augmented reality (AR) visualization were implemented. These approaches include video-see through systems, semitransparent mirrors, modified endoscopes, and modified operating microscopes. Common to all these devices is the fact that a precise calibration between the display and three-dimensional coordinates in the patient's frame of reference is compulsory. In optical see-through devices based on complex optical systems such as operating microscopes or operating binoculars-as in the case of the system presented in this paper-this procedure can become increasingly difficult since precise camera calibration for every focus and zoom position is required. We present a method for fully automatic calibration of the operating binocular Varioscope M5 AR for the full range of zoom and focus settings available. Our method uses a special calibration pattern, a linear guide driven by a stepping motor, and special calibration software. The overlay error in the calibration plane was found to be 0.14-0.91 mm, which is less than 1% of the field of view. Using the motorized calibration rig as presented in the paper, we were also able to assess the dynamic latency when viewing augmentation graphics on a mobile target; spatial displacement due to latency was found to be in the range of 1.1-2.8 mm maximum, the disparity between the true object and its computed overlay represented latency of 0.1 s. We conclude that the automatic calibration method presented in this paper is sufficient in terms of accuracy and time requirements for standard uses of optical see-through systems in a clinical environment.

Algorithms↗
PubMed1986

The spectra, classification, and rationale of ultraviolet-protective intraocular lenses.

I measured the spectral transmittance of 16 implantable intraocular lenses from 12 manufacturers and examined the rationale for using ultraviolet-absorptive intraocular lenses to protect pseudophakic individuals from photic retinopathy. Each ultraviolet-protective lens was classified by the wavelength at which its spectral transmittance fell to 10% in the blue or ultraviolet region of the spectrum. Current ultraviolet-protective intraocular lenses differ in the effectiveness of their protection against photic retinopathy, and product descriptions may be misleading.

Advertising↗
PubMed1998

Retinal nerve fibre layer polarimetry: histological and clinical comparison.

AIMS: To compare histological thickness of the retinal nerve fibre layer in the primate with retardation measurements obtained in vivo using the Mark II Nerve Fiber Analyzer (NFA, Laser Diagnostic Technologies, San Diego, USA). METHODS: Scanning laser polarimetry was performed on both eyes of a healthy anaesthetised adult primate (Macaca mulatta). The retinal nerve fibre layer thickness was measured in the eye with the best polarimetry image. A nerve fibre layer thickness map was scaled and aligned to a retardation map to permit correlation of retardation and thickness measurements. RESULTS: Retinal nerve fibre layer thickness measurements could be satisfactorily aligned with corresponding retardation values at 216 locations. The overall correlation coefficient for nerve fibre layer thickness and retardation was r = 0.70 (n = 216, p < 0.001). Regional comparison showed the best correlation (r = 0.76, n = 45, p < 0.001) occurred inferior to the optic disc. Less positive but still highly significant correlations were seen superiorly and temporally (r = 0.52, n = 26, p = 0.007 and r = 0.49, n = 86, p = < 0.001 respectively), with the lowest correlation occurring at the nasal aspect of the disc (r = 0.06, n = 67, p = 0.64). CONCLUSIONS: In the primate eye, retinal nerve fibre layer thickness shows a positive correlation with retardation measurements obtained with the nerve fibre analyser. However, since the correlation coefficient varied around the optic disc, further evaluation of the device is advised before its routine clinical use.

Animals↗
PubMed2003

Multifunctional double-layered diffractive optical element.

We propose a novel multifunctional double-layered diffractive optical element (DOE) based on the fractional Talbot effect. This DOE consists of two layers: one is the encoding layer, in which multiple sub-DOEs, i.e., multiple optical functions, are encoded; the other is the decoding layer, which is a properly designed Talbot illuminator. This DOE can perform each of the multiple optical functions one by one by shifting the encoding layer. Experimental results demonstrate that this method is efficient. This device should be highly interesting for integrated optics, optical interconnection, secure optical storage, and dynamic optical fiber communications.

Journal Article↗