Conventional Detector System Research Articles

A virtual anti-scatter grid for multi-energy photon counting detector systems

Photon-counting (PC) systems are the next technological generation of medical computed tomography (CT) imaging and is being worked on by all major system providers. CT devices that are based on PC detectors enable multi-energy data collection. The information-content of this data can be used to obtain more detailed patient data, which improves the quality of reconstructions, compared to conventional detector systems. However, PC CT systems are subject to radiation scatter as just as any other imaging systems is. Conventionally anti-scatter grids (ASG) are used to reduce the scatter effect. These are however an imperfect solution, especially for PC detectors. In this work, a software-based scatter correction method, thus a virtual ASG is proposed. The method is tailoring a new statistical model in the measurement space and combining it with the statistical inversion method called Markov chain Monte Carlo (MCMC). The method can recover the measurement data from dense projections. We present the method on simulated data of a single photon emission computed tomography (SPECT) problem for which only under-sampled data is available. However, our approach can in principle be generalised to CT, PC-CT, Positron emission tomography (PET), radiotherapy, or even digital radiography problems. The results show that the proposed model performs similarly as physical ASGs and for cases where ASGs are not possible. The model further offers a significant improvement in the quality of the reconstruction image compared to the image reconstruction from original under-sampled data.

Micro-scale particle tracking using hybrid detectors

Positron Emission Particle Tracking (PEPT) techniques allow the tracking of a radioactive tracer particle moving within a system of flow, enabling non-invasive study of dynamic systems. On the micro-scale, PEPT performance is limited by the achievable activity in radiolabelling a suitable tracer particle, and the fixed geometry of conventional detector systems. To enable application of PEPT towards these scales advanced instrumentation is required, and a hybrid detection system has been developed combining scintillator and semiconductor devices. A bismuth germanate oxide (BGO) scintillator array consisting of 1024 detector elements derived from CTI/Siemens PET scanners (512 pixels of 6.75 x 6.25 x 30 mm3 and 512 pixels of 4.1 x 4.0 x 30 mm3) forms a field of view of 150 x 196 x 101 mm3. A pair of pixelated cadmium zinc telluride room temperature semiconductors (9680 pixels of 1.8 x 1.8 x 0.5 mm3) form a high spatial resolution region of 62 x 42 x 20 mm3 placed within the larger field of view. The design choice maximizes absolute efficiency by merit of the scintillators and enhances spatial resolution through the semiconductors. Energy and timing resolutions of the BGO elements were determined, and sensitivity profiles of the system modelled numerically, enabling the characterization of the system absolute efficiency and spatial resolution. The results suggest the applicability of PEPT in the study of microscale flows for the first time, including investigating flows in capillaries and micro-fluidic devices.

Optical coupling of bio-inspired mustard protein-based bimetallic nanohybrids with propagating surface plasmon polaritons for femtomolar nitrite ion sensing: Cellphone-based portable detection device

Different classes of biologically and environmentally relevant molecules and ions are quantitatively and qualitatively analyzed using the synergistic approach wherein the properties of both the plasmonic nanomaterials and the fluorescent moieties are explored. In this study, such hybrid systems, called plasmophores (or plasmon coupled fluorophores), are investigated using the surface plasmon-coupled emission (SPCE) platform with silver, gold and silver-gold hybrid nano-structures synthesized via sustainable bio-inspired routes. A simple, rapid, user-friendly and green chemistry approach has been adopted using biocompatible mustard protein as both the reducing and capping agent during nanosynthesis. The morphologically and functionally tunable plasmonic nanomaterials were synthesized by simply exposing a mixture of the respective metal ions and protein to UV-light irradiation. Comprehensive analysis of the out-coupled spontaneous emission in the SPCE framework using spacer, cavity and extended cavity nanointerfaces yielded intriguing results, presenting optimum prerequisites for realizing high SPCE enhancements. More than a 950-fold improvement in the fluorescence signal intensity of rhodamine B was demonstrated utilizing the plasmonic cavity hotspots rendered by the hybrid coupling of the propagating surface plasmon polaritons of Ag with localized plasmon resonances of the bimetallic AgAu nanohybrids. The sharply directional and highly polarized SPCE enhancements, realized without increasing the illumination intensity, were utilized for quantitative detection of biologically relevant nitrite ions in drinking water samples at trace concentrations (limit of detection: 0.1 femtomolar). The applicability and relevance of the demonstrated method for sustainable use of plasmonic nanomaterials in photo-plasmonic research is presented by accomplishing the sensing using a cost-effective smartphone camera with a good correlation with the data obtained from a conventional detector system. Hence, the bio-nano-inspired strategy described here reveals several potential opportunities for the development of environmentally benign portable chemosensing devices for utility in academia and industry, especially for low-and-middle income countries.

On the use of positron counting for radio-Assay in nuclear pharmaceutical production

Current techniques for the measurement of radioactivity at various points during PET radiopharmaceutical production and R&D are based on the detection of the annihilation gamma rays from the radionuclide in the labelled compound. The detection systems to measure these gamma rays are usually variations of NaI or CsF scintillation based systems requiring costly and heavy lead shielding to reduce background noise. These detectors inherently suffer from low detection efficiency, high background noise and very poor linearity. They are also unable to provide any reasonably useful position information.A novel positron counting technique is proposed for the radioactivity assay during radiopharmaceutical manufacturing that overcomes these limitations. Detection of positrons instead of gammas offers an unprecedented level of position resolution of the radiation source (down to sub-mm) thanks to the nature of the positron interaction with matter. Counting capability instead of charge integration in the detector brings the sensitivity down to the statistical limits at the same time as offering very high dynamic range and linearity from zero to any arbitrarily high activity.This paper reports on a quantitative comparison between conventional detector systems and the proposed positron counting detector.

Designing a reliable leak bio-detection system for natural gas pipelines

Monitoring of natural gas (NG) pipelines is an important task for economical/safety operation, loss prevention and environmental protection. Timely and reliable leak detection of gas pipeline, therefore, plays a key role in the overall integrity management for the pipeline system. Owing to the various limitations of the currently available techniques and the surveillance area that needs to be covered, the research on new detector systems is still thriving. Biosensors are worldwide considered as a niche technology in the environmental market, since they afford the desired detector capabilities at low cost, provided they have been properly designed/developed and rationally placed/networked/maintained by the aid of operational research techniques. This paper addresses NG leakage surveillance through a robust cooperative/synergistic scheme between biosensors and conventional detector systems; the network is validated in situ and optimized in order to provide reliable information at the required granularity level. The proposed scheme is substantiated through a knowledge based approach and relies on Fuzzy Multicriteria Analysis (FMCA), for selecting the best biosensor design that suits both, the target analyte and the operational micro-environment. This approach is illustrated in the design of leak surveying over a pipeline network in Greece.

Development of the EUV detector for the BepiColombo mission

An ultraviolet spectrometer, PHEBUS (Probing of Hermean Exosphere by Ultraviolet Spectroscopy) that is loaded onto the Mercury Planetary Orbiter in the BepiColombo mission is under development. The instrument, basically consisting of two spectrophotometers (EUV: 50–150 nm, FUV: 145–330 nm) and one scanning mirror, aims at measuring emission lines from molecules, atoms and ions present in the tenuous atmosphere of Mercury. The detectors employ microchannel plates as 2-D photon-counting devices. In order to enhance the quantum detection efficiencies, the surface of the top microchannel plates of EUV detector is covered with photocathode. This method enables us to identify weak atmospheric signatures such as neon (73.5 nm) and argon (104.8 nm), which could not be detected with conventional detector systems. This paper presents measurements of the performance characteristics of potassium bromide and esium iodide photocathodes, which have been evaluated for use in the EUV channel.

Input–output analysis of in vivo photoassimilate translocation using Positron-Emitting Tracer Imaging System (PETIS) data

The Positron-Emitting Tracer Imaging System (PETIS) is introduced for monitoring the distribution of (11)C-labelled photoassimilates in Sorghum. The obtained two-dimensional image data were quantitatively analysed using a transfer function analysis approach. While one half of a Sorghum root in a split root system was treated with either 0, 100, or 500 mM NaCl dissolved in the nutrient solution, tracer images of the root halves and the lower stem section were recorded using PETIS. From the observed tracer levels, parameters were estimated, from which the mean speed of tracer transport and the proportion of tracer moved between specified image positions were deduced. Transport speed varied between 0.7 and 1.8 cm min(-1) with the difference depending on which part of the stem was involved. When data were collected in the lowest 0.5-1 cm of the stem, which included the point where the roots emerge, transport speed was less. Rapid changes in NaCl concentration, from 0 to 100 mM, resulted in short-term increases of assimilate import into the treated root. This response represented a transient osmotic effect, that was compensated for in the medium-term by osmotic adaptation. Higher concentrations of NaCl (500 mM) resulted in distinctly less photoassimilate transport into the treated root half. The present results agree with earlier observations, showing that transport of (11)C-labelled photoassimilates measured with the PETIS detector system can be quantified using the method of input-output analysis. It is worth noting that with the PETIS detector system, areas of interest do not need to be defined until after data collection. This means that unexpected behaviour of a plant organ will be seen, which is not necessarily the case with conventional detector systems looking at predefined areas of interest.

Dramatic Improvements in UXO Detection Using Discrimination and Dual-Mode Sensor Technology

"Dramatic Improvements in UXO Detection Using Discrimination and Dual-Mode Sensor Technology." ASEG Extended Abstracts, 2003(2), p. 1

Development of a gas counter for AMS measurement of 10Be and 26Al of cosmic spherules

A gas counter suited for 10Be- and 26Al-AMS was newly developed at MALT (Micro Analysis Laboratory, Tandem accelerator, Research Center for Nuclear Science and Technology, University of Tokyo). This countermeasures not only the residual energy ( E r) of the incoming ion, but also its energy loss (Δ E) in the medium of the counter. Using this new counter, some improvements were made in 10Be- and 26Al-AMS measurements, with respect to the conventional detector system at MALT in which only E r is obtained by a solid state detector (SSD) set after a passive absorber. 10Be is more clearly separated from 10B in the two-dimensional E r– ΔE spectrum. However, the continuous background which is suspected to be 7Be produced by the reaction 10B(p, α) 7Be at the entrance of the absorber could not be clearly separated. This limits the isobar suppression factor for 10Be-AMS at MALT now. In the case of 26Al measurements, 17O 2+, coming together with 26Al 3+ into the detector, could be clearly separated. Consequently, the background level was well lowered in both cases, 10Be and 26Al. Now, 10Be and 26Al in cosmic spherules which were difficult to measure by the conventional detector system can be measured at MALT.

Secondary Electron Counting Images in SEM

The conventional method of image recording in scanning electron microscopy is photographic recording of the images displayed on a monitor screen of CRT installed with the SEM. An increasing number of works related to the development of computerized systems for digital recording and processing of the image data have been reported But a serious problem exists that the digiatal image data are acquired by discretizing the analogue output of the conventional detector system. In actuality, proportionality between the analogue output and the number of detected electrons is not ensured because of various kinds of noises and nonlinearity which are parasitic with the electronic circuitry. As a solution, we proposed a detection system to measure directly the number of signal electrons. In this paper, we describe electron counting for secondary electron detection in SEM, and show that the electron counting can provide a far better image quality than the analogue output.I. Images by Counting Method and by Analogue MethodThe signal obtained by the counting method is the electron number reaching the detector. This means that the method can eliminate the thermal noise and the fluctuation of the amplification which are parasitically generated during amplification of any type of secondary electron detectors including Everhart-Thornley detector and semiconductor detectors. In addition, noises caused by electronic circuits connected to the detector can be reduced. As shown in Fig.1, even when a primary electron current is lowered to the level less than 1 pA, we could obtain clear images by the counting method as compared with those by the analogue method. It is clear that the electron counting possesses remarkable advantages, as the secondary electron signal becomes weak.

A determination of the vapor pressures of cæsium and rubidium

An ultraviolet spectrometer, PHEBUS (Probing of Hermean Exosphere by Ultraviolet Spectroscopy) that is loaded onto the Mercury Planetary Orbiter in the BepiColombo mission is under development. The instrument, basically consisting of two spectrophotometers (EUV: 50–150 nm, FUV: 145–330 nm) and one scanning mirror, aims at measuring emission lines from molecules, atoms and ions present in the tenuous atmosphere of Mercury. The detectors employ microchannel plates as 2-D photon-counting devices. In order to enhance the quantum detection efficiencies, the surface of the top microchannel plates of EUV detector is covered with photocathode. This method enables us to identify weak atmospheric signatures such as neon (73.5 nm) and argon (104.8 nm), which could not be detected with conventional detector systems. This paper presents measurements of the performance characteristics of potassium bromide and esium iodide photocathodes, which have been evaluated for use in the EUV channel.