Fiber Optic Plate Research Articles

Measurement of diffuse reflectance from combinatorial samples

Using a luminescence spectrometer as a platform, a system of fibre-optic probes was created that allows full colour characterisation, fluorescence and phosphorescence spectra to be recorded in diffuse reflectance and in transmission from thick or thin film arrays of combinatorial samples of diameter down to 2 mm and from liquids. An integrating sphere is not required and the method is more versatile than the instrument's fibre-optic plate reader which has conjoined fibre bundles set at a fixed angle. Incident and detected light is routed via separate optical fibre bundles which remain stationary above or below a two-axis table. The validation and calibration are described. A library of 25 members was scanned for both diffuse reflectance (colour) and fluorescence in less than an hour. The method thus combines techniques that conventionally rely on different instruments and makes them amenable for high throughput libraries.

Scanning elastic scattering spectroscopy detects metastatic breast cancer in sentinel lymph nodes

A novel method for rapidly detecting metastatic breast cancer within excised sentinel lymph node(s) of the axilla is presented. Elastic scattering spectroscopy (ESS) is a point-contact technique that collects broadband optical spectra sensitive to absorption and scattering within the tissue. A statistical discrimination algorithm was generated from a training set of nearly 3000 clinical spectra and used to test clinical spectra collected from an independent set of nodes. Freshly excised nodes were bivalved and mounted under a fiber-optic plate. Stepper motors raster-scanned a fiber-optic probe over the plate to interrogate the node's cut surface, creating a 20x20 grid of spectra. These spectra were analyzed to create a map of cancer risk across the node surface. Rules were developed to convert these maps to a prediction for the presence of cancer in the node. Using these analyses, a leave-one-out cross-validation to optimize discrimination parameters on 128 scanned nodes gave a sensitivity of 69% for detection of clinically relevant metastases (71% for macrometastases) and a specificity of 96%, comparable to literature results for touch imprint cytology, a standard technique for intraoperative diagnosis. ESS has the advantage of not requiring a pathologist to review the tissue sample.

Development and applications of “Mössbauer cameras”

Two different types of “Mossbauer camera” are presented in this review article. The first one uses an imaging technique for γ-rays which are converted to visual light by a Photon-counting Image Acquisition System (PIAS) combined with a Fiber Optic plate with CsI (Tl) Scintillator (FOS), while the second one is a mapping technique for γ-rays which are first focused by a Multi Capillary X-ray lens (MCX), and subsequently electrons and γ-rays are detected as function of the sample position by a micro-channel plate (MCP) and a Si-PIN detector, respectively. A mapping image of a silicon solar cell is shown as an example obtained by the latter system. We also report on the present status in developing a new combined lens for the mapping using a MCX and a Fresnel Zone Plate (FZP) in order to realize a submicron-meter spatial resolution in a laboratory.

Investigation of the Performance of Scintillator-Based CMOS Flat Panel Detectors for X-Ray and Thermal Neutron Imaging

Recent advances in of silicon-based CMOS (complementary metal-oxide-semiconductor) flat panel detectors have resulted in an attractive use of cost-effective radiation imaging devices for X-ray and neutron radiography/tomography system. Indirect detection methods consisted of an X-ray converter (or a scintillator screen) and photodiode arrays are more widely used in high resolution micro-CT (computed tomography), dental and industrial NDT applications. In this study, The terbium-doped gadolinium oxysulfide (Gd2O2 S:Tb, Gadox) scintillator screens with different thickness (several 30-140 m thickness) were directly coupled with a fiber-optic plate (FOP) of a commercially available CMOS imaging device for high resolution X-ray and thermal neutron radiography. The RadEye1 CMOS APS (active pixel sensor) imager having a large active area of 25 × 50 mm2 and 48 m pixel pitch was selected for X-ray and thermal neutron imaging with high resolution. The scintillation properties and imaging performance such as relative light output, linearity and spatial resolution were measured and evaluated under X-ray and thermal neutron beam exposure. The good linearity and high spatial resolution characteristics in X-ray and thermal neutron imaging experiments were achieved by using compact, cost-effective imaging detector with exchangeable Gadox scintillator screens.

Imaging optical fiber pitch deviations in multifiber lightguide structures

A simple method of imaging optical fiber-to-fiber pitch deviations in multifiber lightguides is proposed, which is based on the filtration of spatial frequencies in the pattern formed by a coherent light reflected from the sample edge. A device that implements this method is described and the results of monitoring the quality of fiber optic plates are presented.

Structural design for birefringent holey fiber with a beat length insensitive to wavelength

By combination of two defect structures with positive and negative birefringence, we design a holey fiber with a beat length that is less sensitive to wavelength. The influence of different structural parameters on birefringence of holey fiber is calculated by the finite-difference beam propagation method. A stable beat length can be achieved at some given wavelength window by adjusting the parameters. An almost uniform beat length with a greater than 180 nm bandwidth at 1310 and 1550 nm wavelength windows is obtained, which is useful for the design and fabrication of fiber-optic wave plates with a wide band.

Performance of an X-ray imaging detector based on a structured scintillator

Structured scintillator plates have been fabricated by filling thallium-doped caesium iodide (CsI) into a silicon pore array. Their X-ray imaging properties have been characterized using a standard dental X-ray source and a charge coupled device (CCD) detector. Results indicate that finer structured pore arrays provide superior imaging resolution while their light output is lower. Direct absorption of X-ray quanta in the CCD is a significant contributor of detector noise. This can be avoided by using a thick fibre optic plate or, in certain cases, by using a hot-pixel software algorithm.

Living Optical Elements in the Vertebrate Retina

While cells are mostly transparent they are phase objects that differ in shape and refractive index. Any image that is projected through layers of cells will normally be distorted by refraction, reflection, and scattering. Strangely, the retina of the vertebrate eye is inverted with respect to its optical function and light must pass through several tissue layers before reaching the light-sensitive photoreceptor cells, with each photon having a chance of being scattered. Here we report how nature has optimized this apparently unfavourable situation. We investigated the optical properties of retinal tissue and individual Muller cells, which are radial glial cells spanning the entire thickness of the retina. Using confocal microscopy, quantitative refractometry, and a modified fiber-based dual-beam laser trap, we found that these cells act as optical fibers and guide light, which would otherwise be scattered, from the retinal surface to the photoreceptor cells. Their parallel arrangement in the retina is reminiscent of fiber-optic plates used for low-distortion image transfer. Behind the Muller cells, there seems to be a specific adaptation of the rod photoreceptor nuclei for improved light transmission through the outer nuclear layer of nocturnal animals. These nuclei have an inverted chromatin structure that turns them into micro-lenses channeling the light through the ONL. These findings ascribe a new function to glial cells, demonstrate the first nuclear adaptation for an optical function, and shed new light on the inverted retina as an optical system.

Performance of a Fibre-Optic Sensor for Monitoring Cracks of Concrete, Masonry and Bituminous Elements

Advances in emerging fi bre-optic sensing technology have contributed to the recent development of innovative systems for monitoring the health of civil engineering structures. The main reasons for this development are the reduced weight and dimensions of fi bre-optic sensors, their strong immunity to electromagnetic interference, their improved environmental resistance and their scale fl exibility for small-gauge and long-gauge measurements. In companion papers, an overview of the challenges related to the design and mechanical characterization of a novel fi bre-optic plate sensor for crack monitoring was explained and discussed. The proposed sensor does not require prior knowledge of the locations of cracks, which is a signifi cant advancement over existing crack-monitoring techniques. Moreover, several cracks can be detected, located and monitored using a single fi bre. In this paper, we will fi rst present the results of calibration tests on the crack sensor, which aim at determining the relationship between optical intensity loss and crack opening under static conditions. Then, the performance of the sensors with respect to the detection and monitoring of internal and external fl exural cracks in concrete, masonry and bituminous elements is assessed. Two versions of the sensor were examined. The fi rst version was externally attached to fi bre-reinforced concrete beams and reinforced masonry slabs; the second version was embedded into fi bre-reinforced concrete beams and bituminous slabs. The results presented in this paper demonstrate the viability of implementing the attached and the embedded plate sensors to detect the formation and propagation of internal and external cracks and to measure the crack opening width in a wide range of applications.

Ion Optical Evaluation of a Miniature Double-Focusing Mass Spectrograph

A new miniature double-focusing mass spectrograph has been designed and constructed. The ion optical system was designed based on Mattauch-Herzog geometry. The mass spectrograph employs a focal plane detector consisting of a microchannel plate, a phosphor layer, a fiber-optic plate and a charge-coupled device. For the evaluation of the ion optics of the instrument, the energy and angular focal planes were investigated both experimentally and by simulation. Double focusing was satisfactorily achieved along a straight line over a wide mass range, and the experimental and simulated results were mutually consistent. A second-order element of the transfer matrix was also measured experimentally and proved to be in good agreement with the simulated result.

Development of a Fluorescent Microscope Combined with a Real-time Autoradiography System

For combination with microscope, we developed real-time autoradiography system for micro-scale analysis with adjustment of the CsI(Ti) scintillator thickness for higher resolution and applying tapered fiber optic plate for magnification of autoradiograph image. We combined real-time autoradiography system with an inverted fluorescent microscope so that an autoradiograph image as well as fluorescent image, bright-field image can be acquired at the same time. In the case of observation of sliced soybean stalk traced 45CaCl, the fluorescent and bright-field image was acquired which magnified to 50 times, the autoradiograph image of 45Ca distribution in the tissue was acquired in almost same scale. The new microscopic system which can acquire autoradiograph image of labeled signals (low molecular weight) is expected to develop the signal transduction study and gene expression, combined with fluorescent protein techniques such as GFP etc.

Development of a Real-time Autoradiography System to Analyze the Movement of the Compounds Labeled with .BETA.-ray Emitting Nuclide in a Living Plant

Real-time imaging analysis in a living plant allows studying the mechanism of chemical transport or signal transduction more in detail. We present the real-time autoradiography system to analyze the movement of β-ray emitters in a living plant. The system was consisted of a FOS (a fiber optic plate deposited with CsI(Ti) scintillator) and a GaAsP imaging intensifier unit. Though the resolution is about the same as that of an imaging plate(IP), the sensitivity was more than 10 times higher than that of an IP. Using this system, 32P movement in a young leaf of soybean was analyzed when 32P was supplied from the root.

Characterization studies of two novel active pixel sensors

A United Kingdom consortium (MI3) is founded to develop advanced CMOS image sensors for scientific applications. “Vanilla,” a 520×520 array of active pixels with 25-µm pitch is fabricated in the 0.35-µm 4M2P (4 metal, 2 poly) CMOS process and uses a 3.3-V supply. It has flushed reset circuitry to attain low reset noise and random pixel access for high-speed region-of-interest (ROI) readout. “OPIC” is a 64×72 test structure array of digital pixels with 30-µm pitch, fabricated in 0.25-µm 5M1P (5 metal 1 poly) CMOS process with a 3.3/2.5-V supply. It can perform thresholding via an in-pixel comparator for sparse readout at a high frame rate. Characterization of both sensors is performed under optical illumination and x-ray exposure. For x-ray characterization, both sensors were coupled to a structured thallium-doped cesium iodide (CsI:Tl) scintillator via a fiber optic plate. Vanilla has been found to exhibit 34±3e− read noise and a spectral response of 225±5 mA/W at 500 nm and can read a 6×6 ROI at 24,395 frames/s. OPIC has 46±3e− read noise and can perform sparse readout at up to 3700 frames/s. Based on these results, Vanilla could be employed for applications where only a small portion of the image contains relevant information, while OPIC is suited to high-speed imaging applications.

Empirical electro‐optical and x‐ray performance evaluation of CMOS active pixels sensor for low dose, high resolution x‐ray medical imaging

Monolithic complementary metal oxide semiconductor (CMOS) active pixel sensors with high performance have gained attention in the last few years in many scientific and space applications. In order to evaluate the increasing capabilities of this technology, in particular where low dose high resolution x-ray medical imaging is required, critical electro-optical and physical x-ray performance evaluation was determined. The electro-optical performance includes read noise, full well capacity, interacting quantum efficiency, and pixels cross talk. The x-ray performance, including x-ray sensitivity, modulation transfer function, noise power spectrum, and detection quantum efficiency, has been evaluated in the mammographic energy range. The sensor is a 525 x 525 standard three transistor CMOS active pixel sensor array with more than 75% fill factor and 25 x 25 microm pixel pitch. Reading at 10 f/s, it is found that the sensor has 114 electrons total additive noise, 10(5) electrons full well capacity with shot noise limited operation, and 34% interacting quantum efficiency at 530 nm. Two different structured CsI:Tl phosphors with thickness 95 and 115 microm, respectively, have been optically coupled via a fiber optic plate to the array resulting in two different system configurations. The sensitivity of the two different system configurations was 43 and 47 electrons per x-ray incident on the sensor. The MTF at 10% of the two different system configurations was 9.5 and 9 cycles/mm with detective quantum efficiency of 0.45 and 0.48, respectively, close to zero frequency at approximately 0.44 microC/kg (1.72 mR) detector entrance exposure. The detector was quantum limited at low spatial frequencies and its performance was comparable with high resolution a: Si and charge coupled device based x-ray imagers. The detector also demonstrates almost an order of magnitude lower noise than active matrix flat panel imagers. The results suggest that CMOS active pixel sensors when coupled to structured CsI:Tl can be used for conventional and advanced digital mammography due to their low noise, high resolution performance.

Measurement Accuracy in Phase-Shifting Point Diffraction Interferometer with Two Optical Fibers

A phase-shifting point diffraction interferometer (PS/PDI) with point sources of two single mode optical fibers has been developed, which will be appropriate for the surface figure measurement of large aperture optics on a sub-nanometer scale. To reduce the measurement error factors, a fiber optic plate (FOP) is used as a projection plane for interference pattern. Errors caused by imperfection of optical alignment, such as position of point sources and tilt of FOP, are minimized by analyzing the measured phase data with an original method. Measurement accuracy in the PS/ PDI is estimated with the interference pattern produced by the two optical fiber sources. If inhomogeneity of the FOP and a systematic error of the PS/PDI are eliminated, the measurement accuracy of the present system is estimated to be less than 4nm P-V and 0.7nm rms, respectively, at a measurement wavelength of 632.8 nm.

Image Quality Evaluation of a Highly-Integrated Digital X-ray Imaging Sensor for Dental Intraoral-Imaging Applications

We have developed a highly-integrated digital X-ray imaging sensor based upon a complementarymetal-oxide semiconductor (CMOS) array coupled with a columnar CsI(Tl) scintillator and an X-ray conversion fiberoptic plate for dental intraoral-imaging applications. The sensor consists of a commercially-available CMOS array with a 35 μm × 35 μm pixel size and a 24.1 mm × 31.6 mm active area, and a high-efficiency columnar CsI(Tl) scintillator of 90 μm in thickness directly deposited on a fiberoptic plate of a 6 μm in core size and 1.45 mm in thickness. In this paper, we describe the highly-integrated digital X-ray imaging sensor and evaluate its performance in terms of the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE), as indicators of image quality.

WE‐C‐L100J‐06: Linear Systems Analysis for a New Solid State X‐Ray Image Intensifier (SSXII) Based On Electron‐Multiplying Charge‐Coupled Devices (EMCCDs)

Purpose: To objectively evaluate and optimize performance of a new SSXII using linear‐systems analysis with varying constituent elements. Method and Materials: An imaging module of the SSXII consists of a fluorescent phosphor, a minifying fiber‐optic taper (FOT), and a fiber‐optic plate (FOP) coupled directly to the sensor of an EMCCD camera. An array of such modules is used to achieve the desired field‐of‐view (FOV). Linear‐systems analysis was applied to a module to determine system performance for various combinations of components whose properties were estimated using known physical constants and manufacturer specifications. A 350μm thick CsI(Tl) structured phosphor deposited on an additional FOP was considered in this analysis; however the phosphor may be grown directly on the FOT for improved optical transfer efficiency. New back‐thinned sensors, offering high optical quantum efficiencies (>90%), are also considered. Various FOT minifications were studied to evaluate the tradeoffs between a larger field‐of‐view (FOV) per module and potential DQE degradation. Results: Initial calculations indicate elimination of a FOP in the imaging chain could improve the integral DQE by 30–80%, depending on the FOT minification. Use of a back‐thinned sensor could offer additional improvements of 10–25% over a front‐illuminated EMCCD. Increasing the FOT minification factor from 3:1 to 6:1 would tend to decrease the integral DQE by ∼50%, which could be more than compensated for by making the above two design improvements. Calculated MTFs and DQEs will be presented for various minifications, exposures, and gains. A prototype SSXII (16μm pixels) demonstrated 20 lp/mm bar‐pattern resolution radiographically and fluoroscopic image sequences with exposures of <3 μR/frame. Conclusion: The linear‐systems analysis indicates current designs for the SSXII will provide high‐resolution, low‐noise, real‐time imaging. With component optimization, an acceptable DQE can be maintained with taper minifications as large as 6:1.(Partial support: the UB Foundation and NIH grants R01‐EB002873, R01‐NS43924.)

Characterization of a high-resolution CT scanner prototype for small animals

— At the Department of Physics of the University of Pisa and INFN of Pisa, we have assembled a high-resolution CT scanner prototype for small animals. The prototype will be integrated with the YAP-(S)PET scanner, in order to realize a combined PET\SPECT\CT scanner for small animals. We have characterized the microCT scanner prototype in terms of spatial resolution and noise using three different X-ray detectors. The first detector (Hamamatsu S7199) is composed by a CsI:Tl layer coupled to a CCD via a 1:1 fiber optic plate; the second detector (Radicon Rad-Eye 4) consists in a flat-panel CMOS sensor, directly coupled to a Ga2O2S:Tb scintillator; the third detector is a 1mm thick Si detector, bump-bonded to the Medipix2 readout chip. The first two detectors are based on indirect conversion of X-rays and operate in charge integration mode, while the third is a direct conversion detector and operates in photon counting mode. The characterization was carried out using dedicated phantoms for the measurement of spatial resolution and image noise. The results obtained with the three detectors are compared, in order to evaluate the differences in tomographic performances due to the different characteristics of each detector.

Muller cells are living optical fibers in the vertebrate retina.

Although biological cells are mostly transparent, they are phase objects that differ in shape and refractive index. Any image that is projected through layers of randomly oriented cells will normally be distorted by refraction, reflection, and scattering. Counterintuitively, the retina of the vertebrate eye is inverted with respect to its optical function and light must pass through several tissue layers before reaching the light-detecting photoreceptor cells. Here we report on the specific optical properties of glial cells present in the retina, which might contribute to optimize this apparently unfavorable situation. We investigated intact retinal tissue and individual Müller cells, which are radial glial cells spanning the entire retinal thickness. Müller cells have an extended funnel shape, a higher refractive index than their surrounding tissue, and are oriented along the direction of light propagation. Transmission and reflection confocal microscopy of retinal tissue in vitro and in vivo showed that these cells provide a low-scattering passage for light from the retinal surface to the photoreceptor cells. Using a modified dual-beam laser trap we could also demonstrate that individual Müller cells act as optical fibers. Furthermore, their parallel array in the retina is reminiscent of fiberoptic plates used for low-distortion image transfer. Thus, Müller cells seem to mediate the image transfer through the vertebrate retina with minimal distortion and low loss. This finding elucidates a fundamental feature of the inverted retina as an optical system and ascribes a new function to glial cells.

Advanced compact accelerator neutron generator technology for active neutron interrogation field work

Due to a need for security screening instruments capable of detecting explosives and nuclear materials there is growing interest in neutron generator systems suitable for field use for applications broadly referred to as active neutron interrogation (ANI). Over the past two years Thermo Electron Corporation has developed a suite of different compact accelerator neutron generator products specifically designed for ANI field work to meet this demand. These systems incorporate hermetically-sealed particle accelerator tubes designed to produce fast neutrons using either the deuterium-deuterium (E n = 2.5 MeV) or deuterium-tritium (E n = 14.1 MeV) fusion reactions. Employing next-generation features including advanced sealed-tube accelerator designs, all-digital control electronics and innovative housing configurations these systems are suitable for many different uses. A compact system weighing less than 14 kg (MP 320) with a lifetime exceeding 1000 hours has been developed for portable applications. A system for fixed installations (P 325) has been developed with an operating life exceeding 4500 hours that incorporates specific serviceability features for permanent facilities with difficult-to-access shield blocks. For associated particle imaging (API) investigations a second-generation system (API 120) with an operating life of greater than 1000 hours has been developed for field use in which a high resolution fiber-optic imaging plate is specially configured to take advantage of a neutron point-source spot size of ∼2 mm.