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1
Norlin, Börje. « Photon Counting X-ray Detector Systems ». Licentiate thesis, Mid Sweden University, Department of Information Technology and Media, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-41.
Texte intégralRésumé :
This licentiate thesis concerns the development and characterisation of X-ray imaging detector systems. “Colour” X-ray imaging opens up new perspectives within the fields of medical X-ray diagnosis and also in industrial X-ray quality control. The difference in absorption for different “colours” can be used to discern materials in the object. For instance, this information might be used to identify diseases such as brittle-bone disease. The “colour” of the X-rays can be identified if the detector system can process each X-ray photon individually. Such a detector system is called a “single photon processing” system or, less precise, a “photon counting system”.
With modern technology it is possible to construct photon counting detector systems that can resolve details to a level of approximately 50 µm. However with such small pixels a problem will occur. In a semiconductor detector each absorbed X-ray photon creates a cloud of charge which contributes to the picture achieved. For high photon energies the size of the charge cloud is comparable to 50 µm and might be distributed between several pixels in the picture. Charge sharing is a key problem since, not only is the resolution degenerated, but it also destroys the “colour” information in the picture.
The problem involving charge sharing which limits “colour” X-ray imaging is discussed in this thesis. Image quality, detector effectiveness and “colour correctness” are studied on pixellated detectors from the MEDIPIX collaboration. Characterisation measurements and simulations are compared to be able to understand the physical processes that take place in the detector. Simulations can show pointers for the future development of photon counting X-ray systems. Charge sharing can be suppressed by introducing 3D-detector structures or by developing readout systems which can correct the crosstalk between pixels.
2
HERRERA, LUIS ERNESTO YNOQUIO. « HIGH RESOLUTION PHOTON COUNTING OPTICAL REFLECTOMETRY ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=27673@1.
Texte intégralRésumé :
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
PROGRAMA DE EXCELENCIA ACADEMICA
BOLSA NOTA 10
Neste trabalho são apresentados dois reflectômetros ópticos por contagem de fótons no domínio do tempo para o monitoramento de fibras ópticas. O primeiro foi projetado para obter faixas dinâmicas altas. Demonstrou-se a sua capacidade de sintonização no monitoramento de redes passivas WDM-PON durante o tráfego de dados. 32 dB de faixa dinâmica com 6 m de resolução foram atingidos. O segundo reflectômetro foi projetado para atingir resoluções ultra altas. As aplicações neste caso, além do monitoramento de uma rede TDM-PON de curto alcance, foram na caracterização de redes de Bragg dispersivas e na descrição e modelagem de um fenômeno não reportado antes na literatura, chamado nesta tese de reflexão por curvatura. Foi demonstrada uma resolução menor que 3 cm com faixa dinâmica maior que 14.0 dB.
This thesis presents the development of two photon counting optical time domain reflectometers for fiber optic links monitoring. The first one was focused on high dynamic range. It is demonstrated its tunable capability for a WDM-PON in-service monitoring. 32 dB on dynamic range and a two-point resolution of 6 m is achieved. The second reflectometer was design to accomplish an ultra high resolution. The monitoring of a short TDM-PON is performed. Moreover, due to its high resolution, a chirped fiber Bragg grating is characterized and a non previous reported phenomena, the bend reflection, is shaped and described. It is demonstrated 3 cm two-point resolution and more than 14 dB on dynamic range.
3
Warbuton, Ryan Ellis. « Infrared time-correlated single-photon counting ». Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2259.
Texte intégralRésumé :
This Thesis investigates near infrared ( ~ 1550 nm) time-correlated singlephoton counting, studying the single-photon detectors and some of the potential application areas. Custom designed and fabricated InGaAs/InP single-photon avalanche diode detectors were characterised. Our devices yielded single-photon detection efficiencies of ~10 %, timing jitter of 200 ps, and noise equivalent power comparable to the best commercially available avalanche photodiodes operated in Geiger-mode. The afterpulsing phenomenon which limits the maximum count rate of InGaAs/InP single-photon avalanche diodes has been investigated in detail and activation energies calculated for the traps that cause this problem. This was found to be ~250 meV for all the devices tested, despite their differing structures and growth conditions, and points to the InP multiplication region as the likely location of the traps. Ways of reducing the effects caused by the afterpulsing phenomenon were investigated and sub-Geiger mode operation was studied in detail. This approach enabled freerunning, afterpulsing-free operation at room temperature of an InGaAs/InP singlephoton avalanche diode detector for the first time. Finally, time-of-flight photon counting laser ranging was performed using both singlephoton avalanche diodes and superconducting nanowire single-photon detectors. The use of the latter resulted in a surface to surface depth resolution of 4 mm being achieved at low average laser power at an eye-safe wavelength of 1550 nm.
4
Natarajan, Chandra Mouli. « Superconducting nanowire single-photon detectors for advanced photon-counting applications ». Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2432.
Texte intégralRésumé :
The ability to detect infrared photons is increasingly important in many elds of scienti c endeavour, including astronomy, the life sciences and quantum information science. Improvements in detector performance are urgently required. The Superconducting Nanowire Single-Photon Detector (SNSPD/SSPD) is an emerging single-photon detector technology o ering broadband sensitivity, negligible dark counts and picosecond timing resolution. SNSPDs have the potential to outperform conventional semiconductor-based photon-counting technologies, provided the di culties of low temperature operation can be overcome. This thesis describes how these important challenges have been addressed, enabling the SNSPDs to be used in new applications. A multichannel SNSPD system based on a closed-cycle refrigerator has been constructed and tested. E cient optical coupling has been achieved via carefully aligned optical bre. Fibre-coupled SNSPDs based on (i) NbN on MgO substrates and (ii) NbTiN on oxidised Si substrates have been studied. The latter give enhanced performance at telecom wavelengths, exploiting the re ection from the Si=SiO2 interface. Currently, the detector system houses four NbTiN SNSPDs with average detection e ciency >20% at 1310 nm wavelength. We have employed SNSPDs in the characterisation of quantum waveguide circuits, opening the pathway to operating this promising platform for optical quantum computing for the first time at telecom wavelengths.
5
Dahlman, Nils. « Evaluation of Photon-Counting Spectral Breast Tomosynthesis ». Thesis, KTH, Medicinsk avbildning, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-32051.
Texte intégralRésumé :
The superposition of anatomical structures often greatly impedes detectability in conventional mammography. Spectral imaging and tomosynthesis are two promising methods used for suppression of the anatomical background. The aim of this thesis is to compare and evaluate the benefits of tomosynthesis and spectral imaging, both in combination and separately. A computer model for signal and noise transfer in tomosynthesis was developed and combined with an existing model for spectral imaging. Measurements were performed to validate the models. An ideal-observer detectability index incorporating anatomical noise was used as a figure of merit to compare the different modalities. For detection of a contrast-enhanced tumor in a breast with high anatomical background, the optimum performance for spectral tomosynthesis was found at a tomo-angle of 10 degrees. The improvement was in the order of a factor 10 compared to non-energy-resolved tomosynthesis with the same angular extent. This was supported by clinical results.
6
Chang, Joshua TsuKang. « Tracking system for photon-counting laser radar ». Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41260.
Texte intégralRésumé :
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 107).
The purpose of this thesis is to build the tracking system for a photon-counting laser radar specifically a laser radar that has the ability to perform direct and coherent detection measurement at low signal levels with common laser, optics and detector hardware. The heart of the tracking algorithm is a Kalman filter, and optimal Kalman filter parameters are determined using software simulations. The tracking algorithm was tested against various simulated (software only) and emulated (with actual hardware) trajectories. We also built and tested the real-time tracking system hardware. The algorithms and methods proposed in this thesis achieve the objective of tracking a target at 1,500 km range to within 1-cm accuracy.
by Joshua TsuKang Chang.
M.Eng.
7
Pizzone, Andrea. « Advanced photon counting applications with superconducting detectors ». Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8630/.
Texte intégralRésumé :
Superconducting nanowire single photon detectors (SNSPDs) have emerged as mature detection technology that offers superior performance relative to competing infrared photon counting technologies. SNSPDs have the potential to revolutionize a range of advanced infrared photon counting applications, from quantum information science to remote sensing. The scale up to large area SNSPD arrays or cameras consisting of hundreds or thousands of pixels is limited by efficient readout schemes. This thesis gives a full overview of current SNSPD technology, describing design, fabrication, testing and applications. Prototype 4-pixel SNSPD arrays (30 x 30 µm2 and 60 x 60 µm2) were fabricated, tested and time-division multiplexed via a power combiner. In addition, a photon-number resolved code-division multiplexed 4-pixel array was simulated. Finally, a 100 m calibration-free distributed fibre temperature testbed, based on Raman backscattered photons detected by a single pixel fibre-coupled SNSPD housed in a Gifford McMahon cryostat was experimentally demonstrated with a spatial resolution of approximately 83 cm. At present, it is the longest range distributed thermometer based on SNSPD sensing.
8
Neimert-Andersson, Thomas. « 3D imaging using time-correlated single photon counting ». Thesis, Uppsala University, Signals and Systems Group, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121104.
Texte intégralRésumé :
This project investigates a laser radar system. The system is based on the principles of time-correlated single photon counting, and by measuring the times-of-flight of reflected photons it can find range profiles and perform three-dimensional imaging of scenes. Because of the photon counting technique the resolution and precision that the system can achieve is very high compared to analog systems. These properties make the system interesting for many military applications. For example, the system can be used to interrogate non-cooperative targets at a safe distance in order to gather intelligence. However, signal processing is needed in order to extract the information from the data acquired by the system. This project focuses on the analysis of different signal processing methods.
The Wiener filter and the Richardson-Lucy algorithm are used to deconvolve the data acquired by the photon counting system. In order to find the positions of potential targets different approaches of non-linear least squares methods are tested, as well as a more unconventional method called ESPRIT. The methods are evaluated based on their ability to resolve two targets separated by some known distance and the accuracy with which they calculate the position of a single target, as well as their robustness to noise and their computational burden.
Results show that fitting a curve made of a linear combination of asymmetric super-Gaussians to the data by a method of non-linear least squares manages to accurately resolve targets separated by 1.75 cm, which is the best result of all the methods tested. The accuracy for finding the position of a single target is similar between the methods but ESPRIT has a much faster computation time.
9
Ma, Jiaju. « Photon-Counting Jot Devices for Quanta Image Sensor ». Thesis, Dartmouth College, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10637406.
Texte intégralRésumé :
The quanta image sensor (QIS) is a third-generation solid-state digital imaging technology. The photoelements, called ?jots,? are specialized to have photon-counting sensitivity at room temperature without using electron avalanche multiplication. A QIS may contain billions of jots operating at 1000fps or higher and by counting every single photon at a high speed, numerous exciting features can be enabled. This novel technology can naturally fit the needs of high-speed and high-resolution accurate photon-counting imaging for scientific imaging, space imaging, security, low-light imaging and other applications. A proof of concept for the jot device was successfully developed and demonstrated in 2015 and 2017. Using the innovative jot structure, sub-0.2e- r.m.s. read noise was demonstrated with a manifestly improved conversion gain at room temperature. For the first time, accurate photon counting was realized with photodetectors fabricated in a standard CMOS process without the use of amplification from electron avalanche multiplication. This thesis covers the development of photon-counting jot devices for the QIS. The design of the jot was one of the most difficult challenges in the implementation of the QIS. These difficulties included the reduction of read noise to enable photon-counting while shrinking the size of the jots and optimizing other specifications that affect the accuracy of photon-counting (dark current, quantum efficiency, etc.). The work presented in this thesis covers all of these topics, while the emphasis is placed on the most challenging hurdle: the reduction of read noise towards the deep sub-electron read noise region to enable photon-counting.
10
Michel-Murillo, Raul. « Development of the BIGMIC image photon counting detector ». Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265337.
Texte intégral
11
Verroi, Enrico. « Very fast photon counting photometers for astronomical applications ». Doctoral thesis, Università degli studi di Padova, 2011. http://hdl.handle.net/11577/3421592.
Texte intégralRésumé :
The topics treated in this thesis are the design, the integration and the use of the ultra-fast single photon photometer IQuEYE (Italian Quantum Eye). The implementation of this instrument represents an important step in a project, initiated in 2005, for the realization of a Quantum Photometer (QuantEYE) for the telescope EELT (European Extremely Large Telescope) of 42 meters in diameter, now under construction, which is scheduled for completion in 2018.
Such an instrument would represent a breakthrough in observational Astronomy and it would allow extending the knowledge gained from theoretical and experimental Quantum Optics to the Astrophysics. QuantEYE is designed to extract from the light collected the information enclosed in the statistical distribution of photons through spatial and temporal analysis of the correlation functions of order higher than first, beyond the capability of "classics" instrumentation.
The instrument described in this thesis, IQuEYE, is a prototype for NTT (ESO New Technology Telescope). It is essentially a fixed aperture photometer that collects light within a field of view of few arcseconds, dividing the telescope light beam into four equal parts, and focuses each sub-beam on an independent single photon-counting diode SPAD. The innovative photon time-tagging system is based on a rubidium atomic clock, corrected on long time scale the by means of a GPS signal. This system allows the identification of each photon with a relative precision better than 100ps and an absolute UTC precision of 500ps for an hour of observation. The instrument can identify in this way up to eight million photons per second, that means IQuEYE is able to sustain flows of photons up to a maximum rate of 8MHz. All arrival times, digitized at 25ps, are stored, in this way post-processing analysis and data reprocessing in time are allowed.
The first part of the thesis is devoted to the detailed description of the instrument, starting from design phase, with particular attention for opto-mecanics, to its integration.
IQuEYE is now fully operative and has already been used in three ob-servation campaigns at La Silla (Chile) during the months of January and December 2009 and July-August 2010. The thesis then collects the results of some observations performed and presents them in its second part, with the aim of demonstrating the potential of the instrument.
So a brief description of a first experiment for the feasibility of intensity interferometry is given. Moreover the observation of an exoplanetary transit which allows us to double the accuracy in determining the period of mid-transit, is described. Finally the results for the observation of rapidly varying objects (three optical pulsars) are exposed, together with some analysis tools developed specifically for our data. The acquired data have an excellent quality. Through their analysis the best determination of the Crab pulsar (PSR B0531 +21) period was achieved. Furthermore the optical light curves for PSR B0833-45 (weak pulsar in the Vela constellation, at the limits of visibility for NTT) and B0540-69.
In this way the validity of IQuEYE in HTRA High Time Resolution Astronomy has been demonstrated.Gli argomenti trattati in questa tesi sono la progettazione, l’integrazione e l’utilizzo del fotometro ultrarapido a conteggio di singolo fotone IQuEYE (Italian Quantum Eye). L’implementazione di questo strumento rappresenta un passo fondamentale in un progetto avviato nel 2005 che mira alla realizzazione di un fotometro quantistico, QuantEYE, per il telescopio EELT (European Extremely Large Telescope) di 42 metri di diametro, oggi in fase di costruzione, la cui ultimazione è prevista per il 2018. Un tale strumento rappresenterebbe una svolta nell’astronomia osservativa, permettendo di estendere le conoscenze sviluppate nell’ambito dell’ottica quantistica teorica e sperimentale all’ambito astrofisico. QuantEYE è progettato per estrarre dalla luce raccolta le informazioni contenute nella statistica di distribuzione spaziale e temporale dei fotoni mediante l’analisi delle funzioni di correlazione di ordine superiore al primo, limite al quale si fermano gli strumenti astronomici “classici”. Lo strumento descritto nella presente tesi, IQuEYE, è un prototipo destinato all’uso su NTT (ESO New Technology Telescope). Si tratta essenzialmente di un contatore di singoli fotoni progettato per raccogliere la luce suddividendo la pupilla del telescopio attraverso quattro canali indipendenti che utilizzano dei rivelatori di tipo SPAD. L’innovativo sistema di etichettatura temporale dei fotoni rilevati si basa su un orologio atomico al rubidio, per corregere la deriva del quale viene usato un segnale GPS interpolato su lunga scala temporale. Tale sistema permette di identificare ogni fotone con una precisione relativa migliore di 100ps ed una precisione assoluta riferita ad UTC di 500ps per un’ora di osservazione. Lo strumento è in grado identificare in questo modo fino ad otto milioni di fotoni al secondo, cioè di sostenere flussi di fotoni fino ad un limite massimo di 8MHz. Tutti i tempi di arrivo, digitalizzati a 25ps, vengono salvati e permettono l’analisi differita e la rielaborazione nel tempo. La prima parte della tesi è dedicata alla descrizione dettagliata dello strumento, a partire dalla fase di progettazione, il disegno optomeccanico, fino alla sua integrazione. IQuEYE è oggi perfettamente funzionante ed è stato già utilizzato in tre campagne osservative a La Silla (Cile) durante i mesi di gennaio e dicembre 2009 e luglio-agosto 2010. La tesi raccoglie quindi i risultati di alcune delle osservazioni effettuate e li presenta nella seconda parte, con l’intento di dimostrare le potenzialità dello strumento. Vengono descritti sommariamente un primo esperimento di fattibilità per l’interferometria di intensità e l’osservazione di un transito esoplanetario che permette di raddoppiare la precisione nella determinazione del periodo di metà transito rispetto agli strumenti utilizzati da altri autori. Per finire sono esposti i risultati ottenuti nell’osservazione di oggetti rapidamente variabili, tre pulsar ottiche, e alcuni strumenti di analisi dati sviluppati specificatamente. I dati acquisiti hanno una qualità eccellente e hanno permesso di ottenere la miglior determinazione mai conseguita del periodo di pulsazione per PSR B0531+21 (la pulsar della nebulosa del Granchio). Sono inoltre state ricavate le prime curve di luce ottiche da decenni a questa parte per PSR B0833-45 (debole pulsar nella costellazione della Vela, ai limiti di visibilità per NTT) e per B0540-69. In questo modo la validità di IQuEYE nell’ambito dell’astronomia ad alta risoluzione temporale è stata ampiamente dimostrata.
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Ren, Ximing. « Advanced photon counting techniques for long-range depth imaging ». Thesis, Heriot-Watt University, 2015. http://hdl.handle.net/10399/2980.
Texte intégralRésumé :
The Time-Correlated Single-Photon Counting (TCSPC) technique has emerged as a candidate approach for Light Detection and Ranging (LiDAR) and active depth imaging applications. The work of this Thesis concentrates on the development and investigation of functional TCSPC-based long-range scanning time-of-flight (TOF) depth imaging systems. Although these systems have several different configurations and functions, all can facilitate depth profiling of remote targets at low light levels and with good surface-to-surface depth resolution. Firstly, a Superconducting Nanowire Single-Photon Detector (SNSPD) and an InGaAs/InP Single-Photon Avalanche Diode (SPAD) module were employed for developing kilometre-range TOF depth imaging systems at wavelengths of ~1550 nm. Secondly, a TOF depth imaging system at a wavelength of 817 nm that incorporated a Complementary Metal-Oxide-Semiconductor (CMOS) 32×32 Si-SPAD detector array was developed. This system was used with structured illumination to examine the potential for covert, eye-safe and high-speed depth imaging. In order to improve the light coupling efficiency onto the detectors, the arrayed CMOS Si-SPAD detector chips were integrated with microlens arrays using flip-chip bonding technology. This approach led to the improvement in the fill factor by up to a factor of 15. Thirdly, a multispectral TCSPC-based full-waveform LiDAR system was developed using a tunable broadband pulsed supercontinuum laser source which can provide simultaneous multispectral illumination, at wavelengths of 531, 570, 670 and ~780 nm. The investigated multispectral reflectance data on a tree was used to provide the determination of physiological parameters as a function of the tree depth profile relating to biomass and foliage photosynthetic efficiency. Fourthly, depth images were estimated using spatial correlation techniques in order to reduce the aggregate number of photon required for depth reconstruction with low error. A depth imaging system was characterised and re-configured to reduce the effects of scintillation due to atmospheric turbulence. In addition, depth images were analysed in terms of spatial and depth resolution.
13
Watt, John. « A photon counting pixel detector for X-ray imaging ». Thesis, University of Glasgow, 2001. http://theses.gla.ac.uk/1009/.
Texte intégralRésumé :
Hybrid semiconductor pixel detector technology is presented in this thesis as an alternative to current imaging systems in medical imaging and synchrotron radiation applications. The technology has been developed from research performed in High Energy Physics, in particular, for the ATLAS experiment at the LHC, planned for 2005. This thesis describes work done by the author on behalf of the MEDIPIX project, a collaboration between 13 international institutions for the development of hybrid pixel detectors for non-HEP applications. Chapter 1 describes the motivation for these detectors, the origin of the technology, and the current state of the art in imaging devices. A description of the requirements of medical imaging on X-ray sensors is described, and the properties of film and CCDs are discussed. The work of the RD19 collaboration is introduced to show the evolution of these devices. Chapter 2 presents the basic semiconductor theory required to understand the operation of these detectors, and a section on image theory introduces the fundamental parameters which are necessary to define the quality of an imaging device. Chapter 3 presents measurements made by the author on a photon counting detector (PCD1) comprising a PCC1 (MEDIPIX1) readout chip bumpbonded to silicon and gallium arsenide pixel detectors. Tests on the seperate readout chip and the bump-bonded assembly are shown with comparisons between the performance of the two materials. Measurements of signal-tonoise ratio, detection efficiency and noise performance are presented, along with an MTF measurement made by the Freiburg group. The X-ray tube energy spectrum was calibrated by REGAM. The performance of the PCD in a powder diffraction experiment using a synchrotron radiation source is described in chapter 4. This chapter reports the first use of a true 2-D hybrid pixel detector in a synchrotron application, and a comparison with the existing scintillator based technology is made. The measurements made by the author have been presented at the 1st International Workshop on Radiation Imaging Detectors at Sundsvall, Sweden, June 1999. The PCD1 operates in single photon counting mode, which attempts to overcome the limitations of charge integrating devices such as CCDs. The pros and cons of the two detection methods are discussed in chapter 5, and a comparison was made of the PCD1 performance with the performance of a commercial dental X-ray sensor. The two detectors are compared in terms of contrast and signal-to-noise ratio for identical X-ray fluences. The results were presented at the 2nd International Workshop on Radiation Imaging Detectors, Freiburg, Germany, 2nd-6th July 2000. The author was involved in the conversion of the LabWindows MRS software to a LabView platform, which was presented in an MSc- thesis in the University of Glasgow by F. Doherty. All image processing, data manipulation and analysis code was written by the author.
14
Lapington, Jonathan Stephen. « New techniques for imaging photon counting and particle detectors ». Thesis, University College London (University of London), 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411261.
Texte intégral
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Joynson, Steven. « Photon counting techniques applied to single aerosol particle spectroscopy ». Thesis, Cranfield University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257510.
Texte intégral
16
Niu, Pei. « Multi-energy image reconstruction in spectral photon-counting CT ». Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI022.
Texte intégralRésumé :
Le scanner CT spectral à comptage de photons (sCT) est apparu récemment comme une nouvelle technique d'imagerie présentant des avantages fondamentaux par rapport au scanner CT classique et au scanner CT à double énergie. Cependant, en raison du nombre réduit de photons dans chaque bande d'énergie du scanner sCT et des artéfacts divers, la reconstruction des images devient particulièrement difficile. Cette thèse se concentre sur la reconstruction d'images multi-énergie en sCT. Tout d'abord, nous proposons d'étudier la capacité du scanner sCT à réaliser simultanément une imagerie anatomique (aCT) et fonctionnelle (fCT) en une seule acquisition par reconstruction et décomposition des matériaux. La fonction aCT du scanner sCT est étudiée dans la même configuration que celle du scanner CT classique, et la fonction fCT du scanner sCT est étudiée en appliquant des algorithmes de décomposition de matériaux aux mêmes données multi-énergie. Ensuite, comme le bruit est un problème particulièrement aigu en raison du nombre largement réduit de photons dans chaque bande d'énergie du scanner sCT, nous introduisons un mécanisme de débruitage dans la reconstruction de l'image pour effectuer simultanément un débruitage et une reconstruction. Enfin, pour améliorer la reconstruction de l'image, nous proposons de reconstruire l'image à une bande d'énergie donnée en exploitant les informations dans toutes les autres bandes d'énergie. La stratégie clé de cette approche consiste à regrouper les pixels similaires issus de la reconstruction de toutes les bandes d'énergie en une seule classe, à les ajuster dans la même classe, à projeter les résultats de l'ajustement dans chaque bande d'énergie, et à débruiter les informations projetées. Elle est utilisée à la fois comme une opération post-débruitage pour démontrer son efficacité et comme un terme de régularisation ou un terme de régularisations combinées pour la réalisation simultanée du débruitage et de la reconstruction. Toutes les méthodes ci-dessus sont évaluées sur des données de simulation et des données réelles provenant d'un scanner sCT précliniqueSpectral photon-counting CT (sCT) appeared recently as a new imaging technique presenting fundamental advantages with respect to conventional CT and duel-energy CT. However, due to the reduced number of photons in each energy bin of sCT and various artifacts, image reconstruction becomes particularly difficult. This thesis focuses on the reconstruction of multi-energy images in sCT. First, we propose to consider the ability of sCT to achieve simultaneously both anatomical (aCT) and functional imaging (fCT) in one single acquisition through reconstruction and material decomposition. aCT function of sCT is studied under the same configuration as that of conventional CT, and fCT function of sCT is investigated by applying material decomposition algorithms to the same acquired multi-energy data. Then, since noise is a particularly acute problem due to the largely reduced number of photons in each energy bin of sCT, we introduce denoising mechanism in the image reconstruction to perform simultaneous reconstruction and denoising. Finally, to improve image reconstruction, we propose to reconstruct the image at a given energy bin by exploiting information in all other energy bins. The key strategy in such approach consists of grouping the similar pixels from the reconstruction of all the energy bins into the same class, fitting within each class, mapping the fitting results into each energy bin, and denoising with the mapped information. It is used both as a post-denoising operation to demonstrate its effectiveness and as a regularization term or a combined regularization term for simultaneous reconstruction and denoising. All the above methods are evaluated on both simulation and real data from a pre-clinical sCT system
17
Lopez, Frances Caroline. « Single photon counting system for mammography with synchrotron radiation ». Doctoral thesis, Università degli studi di Trieste, 2013. http://hdl.handle.net/10077/8581.
Texte intégralRésumé :
2011/2012Digital imaging systems for medical applications must be based upon highly efficient detectors to ensure low patient dose. This is considerably important, especially in mammography, because the high sensitivity of the breast to radiation. A mammoraphy system must also provide high spatial and contrast resolution to be able to detect important structures related to breast malignancies. The work performed and described in this thesis is the development of a readout system for a detector optimised for clinical mammography with synchrotron radiation. The detector called PICASSO (Phase Imaging for Clinical Application with Silicon detector and Synchrotron radiatiOn) is developed mainly for the mammography station of the SYRMEP beamline. The detector described in this work is based on Silicon microstrip sensors that are illuminated edge-on. The incoming beam impinging the detector is parallel to the strips of its sensors. This configuration permits high detection efficiency in the energy range that is of interest for mammography. Moreover, the Silicon sensors also allow direct conversion of X-rays. The readout electronics of the Picasso detector works on single-photon counting mode. That is, only signals from photons that are equal or greater than a pre-set threshold are counted, and low freqency noise are automatically rejected. The visibility of small details, normally valuable in mammograms, are maximised because the system is quantum limited, ie, the quality of the image is limited only by the intrinsic fluctuation of the detected photons. Picasso has four layers, each containing three detector modules. The layers are grouped into pairs and arranged one in front of the other along the beam of propagation. The pairs are controlled separately but are working in parallel. The system is a modular detector that implements a read-out system with MYTHEN II ASICs, an embedded Linux-based controller board and a Scientific Linux acquisition workstation. The developed system architecture and its characteristics will be presented. Preliminary imaging tests were perfomed and results with the new system will be presented. Standard mammographic phantoms were imaged and good quality images were obtained at doses comparable with what is delivered in conventional full field mammographic systems. The whole system was able to sustain fast acquisition speeds up to 10ms/frame and runs stable until a breast-equivalent length acquisition is accomplished. A delay between frame of 150μs and delay between controllers of around 750μs is achieved. Phase-contrast imaging has revolutionized the face of mammography with synchrotron radiation in the last ten years as the first clinical phase has been successfully implemented in our facility. This initial step made use of commercial screen-film system producung promising results. Thanks to the coherence and monochromaticity of light coming from synchrotron sources that edge-enhancement in the image is achieved due to phase effects. The compatibility of the Picasso detector to phase-contrast imaging with other novel techniques has also been evaluated in line with this project. Phase-contrast was well demonstrated with the system, details of which will be fully described.
XXV Ciclo
1980
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Wood, Christopher. « Higher order statistics in photon-correlation spectroscopy ». Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267626.
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Shastri, Vasant. « Single-photon-counting technique for luminescence spectra and decay measurements ». Ohio : Ohio University, 1987. http://www.ohiolink.edu/etd/view.cgi?ohiou1183060409.
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Norlin, Börje. « Characterisation and application of photon counting X-ray detector systems ». Doctoral thesis, Mittuniversitetet, Institutionen för informationsteknologi och medier, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-38.
Texte intégralRésumé :
This thesis concerns the development and characterisation of X-ray imaging systems based on single photon processing. “Colour” X-ray imaging opens up new perspectives within the fields of medical X-ray diagnosis and also in industrial X-ray quality control. The difference in absorption for different “colours” can be used to discern materials in the object. For instance, this information might be used to identify diseases such as brittle-bone disease. The “colour” of the X-rays can be identified if the detector system can process each X-ray photon individually. Such a detector system is called a “single photon processing” system or, less precise, a “photon counting system”. With modern technology it is possible to construct photon counting detector systems that can resolve details to a level of approximately 50 µm. However with such small pixels a problem will occur. In a semiconductor detector each absorbed X-ray photon creates a cloud of charge which contributes to the image. For high photon energies the size of the charge cloud is comparable to 50 µm and might be distributed between several pixels in the image. Charge sharing is a key problem since, not only is the resolution degenerated, but it also destroys the “colour” information in the image. This thesis presents characterisation and simulations to provide a detailed understanding of the physical processes concerning charge sharing in detectors from the MEDIPIX collaboration. Charge summing schemes utilising pixel to pixel communications are proposed. Charge sharing can also be suppressed by introducing 3D-detector structures. In the next generation of the MEDIPIX system, Medipix3, charge summing will be implemented. This system, equipped with a 3D-silicon detector, or a thin planar high-Z detector of good quality, has the potential to become a commercial product for medical imaging. This would be beneficial to the public health within the entire European Union.Denna avhandling berör utveckling och karaktärisering av fotonräknande röntgensystem. ”Färgröntgen” öppnar nya perspektiv för medicinsk röntgendiagnostik och även för materialröntgen inom industrin. Skillnaden i absorption av olika ”färger” kan användas för att särskilja olika material i ett objekt. Färginformationen kan till exempel användas i sjukvården för att identifiera benskörhet. Färgen på röntgenfotonen kan identifieras om detektorsystemet kan detektera varje foton individuellt. Sådana detektorsystem kallas ”fotonräknande” system. Med modern teknik är det möjligt att konstruera fotonräknande detektorsystem som kan urskilja detaljer ner till en upplösning på circa 50 µm. Med så små pixlar kommer ett problem att uppstå. I en halvledardetektor ger varje absorberad foton upphov till ett laddningsmoln som bidrar till den erhållna bilden. För höga fotonenergier är storleken på laddningsmolnet jämförbar med 50 µm och molnet kan därför fördelas över flera pixlar i bilden. Laddningsdelning är ett centralt problem delvis på grund av att bildens upplösning försämras, men framför allt för att färginformationen i bilden förstörs. Denna avhandling presenterar karaktärisering och simulering för att ge en mer detaljerad förståelse för fysikaliska processer som bidrar till laddningsdelning i detektorer från MEDIPIX-projekter. Designstrategier för summering av laddning genom kommunikation från pixel till pixel föreslås. Laddningsdelning kan också begränsas genom att introducera detektorkonstruktioner i 3D-struktur. I nästa generation av MEDIPIX-systemet, Medipix3, kommer summering av laddning att vara implementerat. Detta system, utrustat med en 3D-detektor i kisel, eller en tunn plan detektor av högabsorberande material med god kvalitet, har potentialen att kunna kommersialiseras för medicinska röntgensystem. Detta skulle bidra till bättre folkhälsa inom hela Europeiska Unionen.
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Norlin, Börje. « Characterisation and application of photon counting X-ray detector systems / ». Sundsvall : Mittuniversitetet, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-38.
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Nelson, Emily W. (Emily Wyke) 1977. « Counting statistics of a system to produce entangled photon pairs ». Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/86724.
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Persson, Mats. « Spectral Computed Tomography with a Photon-Counting Silicon-Strip Detector ». Doctoral thesis, KTH, Medicinsk bildfysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-187263.
Texte intégralRésumé :
Computed tomography (CT) is a widely used medical imaging modality. By rotating an x-ray tube and an x-ray detector around the patient, a CT scanner is able to measure the x-ray transmission from all directions and form an image of the patient’s interior. CT scanners in clinical use today all use energy-integrating detectors, which measure the total incident energy for each measurement interval. A photon-counting detector, on the other hand, counts the number of incoming photons and can in addition measure the energy of each photon by comparing it to a number of energy thresholds. Using photon- counting detectors in computed tomography could lead to improved signal-to-noise ratio, higher spatial resolution and improved spectral imaging which allows better visualization of contrast agents and more reliable quantitative measurements. In this Thesis, the feasibility of using a photon-counting silicon-strip detector for CT is investigated. In the first part of the Thesis, the necessary performance requirements on such a detector is investigated in two different areas: the detector element homogeneity and the capability of handling high photon fluence rates. A metric of inhomogeneity is proposed and used in a simulation study to evaluate different inhomogeneity compensation methods. Also, the photon fluence rate incident on the detector in a scanner in clinical use today is investigated for different patient sizes through dose rate measurements together with simulations of transmission through patient im- ages. In the second part, a prototype detector module is used to demonstrate new applications enabled by the energy resolution of the detector. The ability to generate material-specific images of contrast agents with iodine and gadolinium is demonstrated. Furthermore, it is shown theoretically and ex- perimentally that interfaces in the image can be visualized by imaging the so-called nonlinear partial volume effect. The results suggest that the studied silicon-strip detector is a promising candidate for photon-counting CT.
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Zanda, Gianmarco. « Development and application of photon counting techniques for fluorescence microscopy ». Thesis, King's College London (University of London), 2016. http://kclpure.kcl.ac.uk/portal/en/theses/development-and-application-of-photon-counting-techniques-for-fluorescence-microscopy(60d0738e-2523-47c4-b361-4b88ee35b811).html.
Texte intégralRésumé :
Fluorescence lifetime imaging microscopy (FLIM) is a key technique to image cells as, in addition to the advantages of standard fluorescence microscopy, it allows to study the environment and probe interaction in living specimens. Implementing FLIM via Single Photon Counting (SPC) proved to be the most effective technique considering the fluorophores limited photon budget before being irreversibly bleached. This thesis focuses on the development and application of Single Photon Counting techniques to imaging systems and to spectroscopy. Firstly, the BODIPY-C12 molecular rotor was used to determine dyeconcentrations between 3 and 16 μM for living cells and lipid droplets via FLIM and intensity measurements A novel compound, named ET, was tested for the first time on living cells and its possible applications as a molecular rotor discussed. The use of an Electron Bombarded Charge-Coupled Device (EBCCD) camera as a parallel-processing Time to Amplitude Converter device for SPC Imaging with sub-frame exposure time resolution was investigated and, although not implemented, the results supports the proposed method. In order to design a wide field time-correlated single photon counting system, a Complementary Metal-Oxide Semiconductor (CMOS) Fast- Camera was coupled with an 3-stage image intensifier. This proved to be suitable for luminescence lifetime measurements of a Ruthenium complex, with results of 1.7μs comparable with confocal scanning Time-Correlated SPC (TCSPC). Finally, conclusions and future work are discussed.
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Pawlikowska, Agata M. « Single-photon counting lidar for long-range three-dimensional imaging ». Thesis, Heriot-Watt University, 2016. http://hdl.handle.net/10399/3173.
Texte intégralRésumé :
Single-photon time-of-flight (ToF) distance ranging lidar is a candidate technology for high-resolution depth imaging for use, for example, from airborne platforms. This approach enables low average power pulsed laser sources to be used while allowing imaging from significantly longer target ranges compared to analogue imaging. The recent availability of Geiger-mode (Gm) arrays has revolutionised photon-counting lidar as they provide single-photon full-frame data in short acquisition times. This thesis presents work on the opto-mechanical design, tolerance analysis and performance evaluation of a re-configurable single-photon counting lidar which can accommodate either a single-element single-photon avalanche photodiode (SPAD) or a 32 × 32 Gm-array. By incorporating an inter-changeable lens, the two configurations were designed to provide identical pixel resolution for both the single-pixel system and the Gm-array configurations in order to permit a performance comparison to be conducted. This is the first time that such a comparison has been reported and the lidar is one of the earliest to assess the performance of a short-wave infra-red (SWIR) Gm-array. Both detection configurations used InGaAs/InP SPAD detectors and operated at a wavelength of 1550 nm. The main benefits of operating within the SWIR band include reduced solar background, lower atmospheric loss, improved covertness, as well as improved laser eye-safety thresholds. The system estimates target range by measuring the ToF using time-correlated single-photon counting (TCSPC) and was used to produce high-resolution three-dimensional images of targets at between 800 m and 10.5 km range. The single-element system has the potential to provide improved depth resolution over the array due to a smaller timing jitter but requires longer acquisition times due to the need for two-dimensional scanning. The acquisition time of the array configuration can be up to three orders of magnitude faster than the single-element configuration but requires significantly higher average laser power levels. The Gm-array provided a simultaneous estimation of angle-of-arrival and intensity fluctuations from which a comparable strength of atmospheric turbulence could be measured. This demonstrated that Gm-arrays provide a new way of high-speed turbulence measurement with time intervals much shorter than those offered by existing scintillometers.
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Moro, Viggo. « Deep-learning image reconstruction for photon-counting spectral computed tomography ». Thesis, KTH, Skolan för teknikvetenskap (SCI), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297560.
Texte intégralRésumé :
X-ray computed tomography (CT) has since its introduction in the early 1970s become one of the most important tools used for medical imaging. In CT, a large number of x-ray attenuation measurements are combined and reconstructed to form a three-dimensional image of the targeted area. In the recent years, a new type of detector called photon counting detector (PCD) has attracted considerable interest. This new type of detector acquires spectral information is associated with several benefits and has shown to be very valuable. Furthermore, the use of deep learning to reconstruct images produced by CT has attracted significant attention in the last couple of years. However, the best way of incorporating deep learning into the reconstruction chain into the reconstruction chain is still incompletely understood. Additionally, the use of deep learning has mainly been investigated for the case of conventional CT and not for CT performed with PCDs. It these two points that this work aims to address. Multiple deep learning architectures were implemented and evaluated on material images acquired by simulating a PCD. The deep-learning part of the reconstruction took the form of image-domain denoising after the material images had been obtained from the material sinograms through filtered back projection. Then, a comparison between the different deep learning architectures was made to find out which architecture is the most suited for denoising images produced by PCDs in the image domain.
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Strasburg, Jana Dee. « Characterization of avalanche photodiode arrays for temporally resolved photon counting / ». Thesis, Connect to this title online ; UW restricted, 2004. http://hdl.handle.net/1773/9710.
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Ekström, Joakim. « 3D Imaging Using Photon Counting Lidar on a Moving Platform ». Thesis, Linköpings universitet, Reglerteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-153297.
Texte intégralRésumé :
The problem of constructing high quality point clouds based on measurements from a moving and rotating single-photon counting lidar is considered in this report. The movement is along a straight rail while the lidar sensor rotates side to side. The point clouds are constructed in three steps, which are all studied in this master’s thesis. First, point clouds are constructed from raw lidar measurements from single sweeps with the lidar. In the second step, the sensor transformation between the point clouds constructed in the first step are obtained in a registration step using iterative closest point (ICP). In the third step the point clouds are combined to a coherent point cloud, using the full measurement. A method using simultaneous localization and mapping (SLAM) is developed for the third step. It is then compared to two other methods, constructing the final point cloud only using the registration, and to utilize odometric information in the combination step. It is also investigated which voxel discretization that should be used when extracting the point clouds. The methods developed are evaluated using experimental data from a prototype photon counting lidar system. The results show that the voxel discretization need to be at least as large as the range quantization in the lidar. No significant difference between using registration and SLAM in the third step is observed, but both methods outperform the odometric method.
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Fancey, Stuart James. « Single-photon avalanche diodes for time-resolved photoluminescence measurements in the near infra-red ». Thesis, Heriot-Watt University, 1996. http://hdl.handle.net/10399/1309.
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Fredenberg, Erik. « Spectral Mammography with X-Ray Optics and a Photon-Counting Detector ». Doctoral thesis, KTH, Medicinsk avbildning, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11641.
Texte intégralRésumé :
Early detection is vital to successfully treating breast cancer, and mammography screening is the most efficient and wide-spread method to reach this goal. Imaging low-contrast targets, while minimizing the radiation exposure to a large population is, however, a major challenge. Optimizing the image quality per unit radiation dose is therefore essential. In this thesis, two optimization schemes with respect to x-ray photon energy have been investigated: filtering the incident spectrum with refractive x-ray optics (spectral shaping), and utilizing the transmitted spectrum with energy-resolved photon-counting detectors (spectral imaging). Two types of x-ray lenses were experimentally characterized, and modeled using ray tracing, field propagation, and geometrical optics. Spectral shaping reduced dose approximately 20% compared to an absorption-filtered reference system with the same signal-to-noise ratio, scan time, and spatial resolution. In addition, a focusing pre-object collimator based on the same type of optics reduced divergence of the radiation and improved photon economy by about 50%. A photon-counting silicon detector was investigated in terms of energy resolution and its feasibility for spectral imaging. Contrast-enhanced tumor imaging with a system based on the detector was characterized and optimized with a model that took anatomical noise into account. Improvement in an ideal-observer detectability index by a factor of 2 to 8 over that obtained by conventional absorption imaging was found for different levels of anatomical noise and breast density. Increased conspicuity was confirmed by experiment. Further, the model was extended to include imaging of unenhanced lesions. Detectability of microcalcifications increased no more than a few percent, whereas the ability to detect large tumors might improve on the order of 50% despite the low attenuation difference between glandular and cancerous tissue. It is clear that inclusion of anatomical noise and imaging task in spectral optimization may yield completely different results than an analysis based solely on quantum noise.QC 20100714
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Xu, Cheng. « A Segmented Silicon Strip Detector for Photon-Counting Spectral Computed Tomography ». Doctoral thesis, KTH, Medicinsk avbildning, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-105614.
Texte intégralRésumé :
Spectral computed tomography with energy-resolving detectors has a potential to improve the detectability of images and correspondingly reduce the radiation dose to patients by extracting and properly using the energy information in the broad x-ray spectrum. A silicon photon-counting detector has been developed for spectral CT and it has successfully solved the problem of high photon flux in clinical CT applications by adopting the segmented detector structure and operating the detector in edge-on geometry. The detector was evaluated by both the simulation and measurements. The effects of energy loss and charge sharing on the energy response of this segmented silicon strip detector with different pixel sizes were investigated by Monte Carlo simulation and a comparison to pixelated CdTe detectors is presented. The validity of spherical approximations of initial charge cloud shape in silicon detectors was evaluated and a more accurate statistical model has been proposed. A photon-counting energy-resolving application specific integrated circuit (ASIC) developed for spectral CT was characterized extensively by electrical pulses, pulsed laser and real x-ray photons from both the synchrotron and an x-ray tube. It has been demonstrated that the ASIC performs as designed. A noise level of 1.09 keV RMS has been measured and a threshold dispersion of 0.89 keV RMS has been determined. The count rate performance of the ASIC in terms of count loss and energy resolution was evaluated by real x-rays and promising results have been obtained. The segmented silicon strip detector was evaluated using synchrotron radiation. An energy resolution of 16.1% has been determined with 22 keV photons in the lowest flux limit, which deteriorates to 21.5% at an input count rate of 100 Mcps mm−2. The fraction of charge shared events has been estimated and found to be 11.1% for 22 keV and 15.3% for 30 keV. A lower fraction of charge shared events and an improved energy resolution can be expected by applying a higher bias voltage to the detector.QC 20121123
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Dalgarno, Paul Allan. « Time correlated single photon counting on charge tunable semiconductor quantum dots ». Thesis, Heriot-Watt University, 2005. http://hdl.handle.net/10399/202.
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Krichel, Nils Johannes. « Long-range depth profiling based on time-correlated single-photon counting ». Thesis, Heriot-Watt University, 2011. http://hdl.handle.net/10399/2475.
Texte intégralRésumé :
Single-photon detection technologies are of high relevance to light detection and ranging (LiDAR) applications for the range resolution and surface profiling of distant target objects. Modern single-photon detectors offer high quantum efficiencies and small timing jitters in the order of tens of ps, allowing for the rapid acquisition of high-resolution time-of-flight information with eye-safe illumination powers. In time-correlated single-photon counting (TCSPC), every detection event is treated as an independent measurement of time. The build-up of photon statistics over many measurement cycles allows for time-of-flight measurements with a precision that can be superior to the system’s single-shot timing uncertainty. This Thesis presents work on a scanning, long-range depth profiler based on TCSPC. Its design is discussed and a comprehensive set of performance metrics is evaluated, serving as the base for a theoretical performance model. Beside measurements at an illumination wavelength of 842 nm, the operation of the system at 1.56 m is also described. A special focus is made on the implementation and evaluation of different single-photon detection modules, including a novel, resonant-cavity-enhanced single-photon avalanche diode. A new data acquisition mode for TCSPC applications was developed to facilitate performance evaluation. Depth uncertainties of 250 m were achieved with the system at 320 m stand-off distance, and a pattern matching scheme was implemented to acquire unambiguous photon-counting depth images at a record-breaking target distance of 4.4 km while maintaining eye-safe illumination levels. Advanced return analysis algorithms were used to demonstrate the automatic resolution of multiple target surfaces.
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Carramate, Lara Filipa das Neves Dias. « Development of a single photon counting computed tomography system using MPGDs ». Doctoral thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14003.
Texte intégralRésumé :
Desenvolvimento de um sistema de tomografia computorizada de contagem de fotão único usando MPGDsThe development of computed tomography systems with energy resolving detectors is a current challenge in medical physics and biomedical engineering. A computed tomography system of this kind allows getting complementary informations relatively to conventional systems, that can help the medical diagnosis, being of great interest in medicine. The work described in this thesis is related to the development of a computed tomography system using micropattern gaseous detectors, which allow storing, simultaneously, information about the interaction position and the energy of each single photon that interacts with the detector. This kind of detectors has other advantages concerning the cost and characteristics of operation when compared with solid state detectors. Tomographic acquisitions were performed using a MicroHole & Strip Plate based detector, which allowed reconstructing cross-sectional images using energy windows, applying the energy weighting technique and performing multi-slice and tri-dimensional reconstructions. The contrast-to-noise ratio was improved by 31% by applying the energy weighting technique, comparing with the corresponding image obtained with the current medical systems. A prototype of a computed tomography with flexibility to change the detector was developed, making it possible to apply different detectors based on Thick-COBRA. Several images acquired with these detectors are presented and demonstrate their applicability in X-ray imaging. When operating in NeCH4, the detector allowed a charge gain of 8 104, an energy resolution of 20% (full width at half maximum at 8 keV), a count rate of 1 106 Hz/mm2, a very stable operation (gain fluctuations below 5%) and a spacial resolution of 1.2 mm for an energy photon of 3.6 keV. Operating the detector in pure Kr allowed increasing the detection efficiency and achieving a charge gain of 2 104, an energy resolution of 32% (full width at half maximum at 22 keV), a count rate of 1 105 Hz/mm2, very stable operation and a spatial resolution of 500 m. The software already existing in the group was improved and tools to correct geometric misalignments of the system were also developed. The reconstructions obtained after geometrical correction are free of artefacts due to the referred misalignments.
O desenvolvimento de sistemas de tomografia computorizada que incorporem detetores com resolução em energia é um desafio atual em física médica e engenharia biomédica. Um sistema de tomografia computorizada espetral permite obter informações complementares comparativamente a um sistema convencional, que podem auxiliar no diagnóstico médico, sendo por isso de grande interesse em medicina. O trabalho exposto nesta tese prende-se com o desenvolvimento de um sistema de tomografia usando detetores gasosos microestruturados que permitem, simultaneamente, ter informação da posição de interacção e da energia de cada fotão que interage com o detetor. Este tipo de detetores possui ainda outras vantagens relativamente a custo ou características de funcionamento quando comparados com detetores de estado sólido. Foram realizadas aquisições tomográficas usando um detetor baseado numa MicroHole & Srip Plate que permitiu reconstruir imagens utilizando diferentes gamas de energia, aplicar técnicas de ponderação em energia e fazer pela primeira vez reconstrução multi-corte e obter imagens tri-dimensionais. Aplicando a técnica de ponderação em energia foi possível melhorar a relação contraste-ruído em 31% comparativamente à imagem correspondente aquela obtida nos actuais sistemas médicos. Posteriormente, foi desenvolvido um protótipo de um sistema de tomografia computorizada com flexibilidade para alterar o detetor, tornando possível utilizar vários detetores baseados na microestrutura Thick-COBRA. São apresentadas várias imagens adquiridas com estes detetores que evidenciam a sua aplicabilidade em imagiologia por raio-X. A operar no meio gasoso NeCH4 o detetor permitiu um ganho de 8 104, uma resolução em energia de 20% (largura a meia altura a 8 keV), uma taxa de contagem de 1 106 Hz/mm2, um funcionamento muito estável (variações de ganho inferiores a 5%) e uma resolução espacial de 1.2 mm para fotões de 3.6 keV. A operar em Kr puro foi possível aumentar a eficiência de deteção e alcançar um ganho de 2 104, uma resolução em energia de 32% (largura a meia altura a 22 keV), uma taxa de contagem de 1 105 Hz/mm2, um funcionamento também bastante estável e uma resolução espacial de 500 m. O software já existente no grupo para reconstrução de imagem foi melhorado e foram ainda desenvolvidas ferramentas para correcção de desalinhamentos geométricos do sistema. As reconstruções obtidas após correção geométrica surgem livres de artefactos originados pelos referidos desalinhamentos.
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Andersson, Måns. « On the usage of a photon counting CT detector for SPECT ». Thesis, KTH, Skolan för teknikvetenskap (SCI), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-210832.
Texte intégralRésumé :
This work explores the possibility of using a photon counting silicon detector developedfor Computer Tomography (CT) in Single Photon Emission Computed Tomography(SPECT) applications. This would allow for a more versatile and a much cheapersystem. The main focus is on determining the efficiency and resolution of such a system.This is done initially via an geometric model evaluating the solid angle of the collimator,showing promising results versus a standard Low Energy High Resolution (LEHR)collimator. Secondly a Monte-Carlo simulation is used for a more in depth analysis ofthe detector response by using two different radionuclides. The performance is measuredwith reference to efficiency and scatter to primary ratio (s/p). The energy thresholdsfor binning is evaluated with a Signal-Difference-to-Noise Ratio (SDNR). A Point SpreadFunction (PSF) is simulated with and without the impact from a human-like phantom.The work concludes that an implementation would not likely to be able to compete withspecialised myocardium SPECT due too the high noise from the detector response whena high efficiency threshold is set. Further investigations in general SPECT applicationsis recommended.Sammanfattning
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Schindhelm, Eric R., J. C. Green, Oswald H. W. Siegmund, Camden Ertley, Brian T. Fleming, Kevin C. France, Walter M. Harris, Alex Harwit, Stephan R. McCandliss et John V. Vallerga. « Microchannel plate detector technology potential for LUVOIR and HabEx ». SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/626502.
Texte intégralRésumé :
Microchannel plate (MCP) detectors have been the detector of choice for ultraviolet (UV) instruments onboard many NASA missions. These detectors have many advantages, including high spatial resolution (<20 mu m), photon counting, radiation hardness, large formats (up to 20 cm), and ability for curved focal plane matching. Novel borosilicate glass MCPs with atomic layer deposition combine extremely low backgrounds, high strength, and tunable secondary electron yield. GaN and combinations of bialkali/alkali halide photocathodes show promise for broadband, higher quantum efficiency. Cross-strip anodes combined with compact ASIC readout electronics enable high spatial resolution over large formats with high dynamic range. The technology readiness levels of these technologies are each being advanced through research grants for laboratory testing and rocket flights. Combining these capabilities would be ideal for UV instruments onboard the Large UV/Optical/IR Surveyor (LUVOIR) and the Habitable Exoplanet Imaging Mission (HABEX) concepts currently under study for NASA's Astrophysics Decadal Survey.
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Åslund, Magnus. « Digital Mammography with a Photon Counting Detector in a Scanned Multislit Geometry ». Doctoral thesis, KTH, Fysik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4322.
Texte intégralRésumé :
Mammography screening aims to reduce the number of breast cancer deaths by early detection of the disease, which is one of the leading causes of deaths for middle aged women in the western world. The risk from the x-ray radiation in mammography is relatively low but still a factor in the benefit-risk ratio of screening. The characterization and optimization of a digital mammography system is presented in this thesis. The investigated system is shown to be highly dose efficient by employing a photon counting detector in a scanning multislit geometry. A novel automatic exposure control (AEC) is proposed and validated in clinical practise. The AEC uses the leading detector edge to measure the transmission of the breast. The exposure is modulated by altering the scan velocity during the scan. A W-Al anode-filter combination is proposed. The characterization of the photon counting detector is performed using the detective quantum efficiency. The effect of the photon counting detector and the multislit geometry on the measurement method is studied in detail. It is shown that the detector has a zero-frequency DQE of over 70\% and that it is quantum limited even at very low exposures. Efficient rejection of image-degrading secondary radiation is fundamental for a dose efficient system. The efficiency of the scatter rejection techniques currently used are quantified and compared to the multislit geometry. A system performance metric with its foundation in statistical decision theory is discussed. It is argued that a photon counting multislit system can operate at approximately half the dose compared to several other digital mammography techniques.QC 20100825
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Åslund, Magnus. « Digital mammography with a photon counting detector in a scanned multislit geometry / ». Stockholm : Fysik, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4322.
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Januszewska, Anna Maria. « Statistical analysis of photon counting histogram with application to receptor structure studies ». Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546503.
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Yveborg, Moa. « Quantification and Maximization of Performance Measures for Photon Counting Spectral Computed Tomography ». Doctoral thesis, KTH, Medicinsk bildfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160899.
Texte intégralRésumé :
During my time as a PhD student at the Physics of Medical Imaging group at KTH, I have taken part in the work of developing a photon counting spectrally resolved silicon detector for clinical computed tomography. This work has largely motivated the direction of my research, and is the main reason for my focus on certain issues. Early in the work, a need to quantify and optimize the performance of a spectrally resolved detector was identified. A large part of my work have thus consisted of reviewing conventional methods used for performance quantification and optimization in computed tomography, and identifying which are best suited for the characterization of a spectrally resolved system. In addition, my work has included comparisons of conventional systems with the detector we are developing. The collected result after a little more than four years of work are four publications and three conference papers. This compilation thesis consists of five introductory chapters and my four publications. The introductory chapters are not self-contained in the sense that the theory and results from all my published work are included. Rather, they are written with the purpose of being a context in which the papers should be read. The first two chapters treat the general purpose of the introductory chapters, and the theory of computed tomography including the distinction between conventional, non-spectral, computed tomography, and different practical implementations of spectral computed tomography. The second chapter consists of a review of the conventional methods developed for quantification and optimization of image quality in terms of detectability and signal-to-noise ratio, part of which are included in my published work. In addition, the theory on which the method of material basis decomposition is based on is presented, together with a condensed version of the results from my work on the comparison of two systems with fundamentally different practical solutions for material quantification. In the fourth chapter, previously unpublished measurements on the photon counting spectrally resolved detector we are developing are presented, and compared to Monte Carlo simulations. In the fifth and final chapter, a summary of the appended publications is included.QC 20150303
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Xie, Bingqing. « Image-domain material decomposition in spectral photon-counting CT for medical applications ». Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI021.
Texte intégralRésumé :
La décomposition de matériaux est un problème fondamental et primordial dans la tomographie spectrale (sCT—spectral computed tomography) par rayons X basée sur des détecteurs à comptage de photons (PCD—photon counting detector). La présente thèse porte sur le développement de méthodes de décomposition de matériaux en utilisant des informations spectrale et morphologique encodées dans des images sCT multi-énergie. Dans ce cadre, trois méthodes ont été développées. Pour la première méthode, en utilisant la densité de masse limitée, la parcimonie conjointe locale, et le faible rang structurel (DSR) dans le domaine de l'image, nous obtenons une décomposition très précise de matériaux tels que le gadolinium, l'iode et le fer. Les résultats sur les données numériques et physiques du fantôme ont démontré que la méthode DSR proposée conduit à une décomposition plus précise que la méthode pseudo-inverse habituelle avec décomposition en valeur singulière (SVD—singular value decomposition) et la méthode de régularisation parcimonieuse courante avec contrainte de norme L1 (lasso). La deuxième méthode opère par région. Elle consiste à optimiser les matériaux de base en se basant sur la segmentation spatio-énergétique des régions d'intérêt (ROI—regions-of-interests) dans les images sCT, à réduire le bruit en faisant le moyennage des images spatiales multi-énergie, et à effectuer une décomposition fine des matériaux impliquant une matrice de décomposition optimisée, une régularisation du débruitage et une régularisation parcimonieuse. Les résultats sur des données numériques et physiques ont montré que la méthode proposée de décomposition des matériaux ROI par ROI (ROI-wise—region-of-interests-wise) présente une fiabilité et une précision nettement supérieures à celles des méthodes de décomposition courantes fondées sur la régularisation de la variation totale (TV) ou de la norme L1. Dans la troisième méthode, nous proposons la notion d'imagerie sCT à super-résolution énergétique (SER—super-energy-resolution), qui est réalisée en établissant la relation entre la simulation et les fantômes physiques au moyen d'un apprentissage par dictionnaire couplé, de manière pixel par pixel. L'efficacité de ces méthodes proposées a été validée sur des données de fantômes numériques, de fantômes physiques et in vivo. Les résultats montrent que, pour la même méthode de décomposition de matériaux utilisant la régularisation par lasso, l'imagerie à super-résolution énergétique proposée présente une précision de décomposition et un pouvoir de détection beaucoup plus élevé que ce que peut fournir la machine sCT actuelleMaterial decomposition is a fundamental and primordial problem in spectral photon-counting X-ray CT (sCT). The present thesis focuses on the development of material decomposition methods using spectral and morphological information embedded in multi-energy sCT images. In this framework, three methods were developed. For the first method, by using bounded mass density, local joint sparsity and structural low-rank (DSR) in image domain, we achieve highly accurate decomposition of materials such as gadolinium, iodine and iron. The results on both numerical phantom and physical data demonstrated that the proposed DSR method leads to more accurate decomposition than usual pseudo-inverse method with singular value decomposition (SVD) and current popular sparse regularization method with L1-norm constraint. The second method works in a region-wise manner. It consists in optimizing basis materials based on spatio-energy segmentation of regions-of-interests (ROIs) in sCT images, reducing noise by averaging multi-energy spatial images, and performing a fine material decomposition involving optimized decomposition matrix, denoising regularization and sparsity regularization. The results on both digital and physical data showed that the proposed ROI-wise material decomposition method presents clearly higher reliability and accuracy compared to common decomposition methods based on total variation (TV) or L1-norm (lasso) regularization. In the third method, we propose the notion of super-energy-resolution (SER) sCT imaging, which is realized through establishing the relationship between simulation and physical phantoms by means of coupled dictionary learning in a pixel-wise way. The effectiveness of the proposed methods was validated on digital phantom, physical phantoms and in vivo data. The results showed that for the same decomposition method using lasso regularization, the proposed super-energy-resolution imaging presents much higher decomposition accuracy and detection ability compared to what can be provided by current sCT machine
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Zhang, Po. « High-resolution Photon Counting OTDR based Interrogation of Multiplexing Broadband FBG Sensors ». Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/11064.
Texte intégralRésumé :
Fiber-optic Bragg grating (FBG) sensors are a very attractive technology for the measurement of strain and temperature. They have many advantages over conventional sensors in sensing applications such as sensitivity, immunity to electromagnetic interferences,large bandwidths,capability of remote operation and the potential power to sense micro strain at high temperature. They can be directly embedded into many structures such as concrete to evaluate the material deformation.
FBGs are fabricated by photo-inscribing through a phase mask technology on a photosensitive fiber. A periodic refractive index is formed in the fiber core, introducing a reflection at the Bragg wavelength. Since the FBG is characterized by a low insertion loss and controllable reflectance, it has the potential to be multiplexed in very large numbers.
The major purpose of this dissertation research is to develop an innovative, high- resolution fiber Bragg grating sensing system using photon-counting optical time domain reflectometry (pc-OTDR) based multiplexing technology. The system uses a Fresnel reflection OTDR with a zero deadzone to detect FBG sensors, which improves both the system detection ability and spatial resolution.
A low reflectance FBG with broad bandwidth has been developed that is appropriate for the pc-OTDR measurement. Hundred of multiplexed sensors have been implemented in this system. Two theoretical analyses and preliminary results are presented. The greatest advantage of the system is to increase the maximum multiplexing sensor number to one thousand within a short fiber range.
Self-referencing demodulation is necessary to eliminate multiplexed system noise caused by the source power fluctuation and fiber bending effects. A referencing FBG with a different wavelength from the sensing FBG has to be introduced to achieve compensation of disturbances in the measurement. The spectral properties of the FBGs and the combination of WDM/TDM are also discussed to evaluate multiplexing sensor performance. The sensor crosstalk and other noise performances are assessed to evaluate the possibility of large scale multiplexing.Ph. D.
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Hallensleben, Sebastian. « Enhanced sensitivity and speed in photomultiplier tubes ». Thesis, University of Sussex, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323025.
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Norton, Timothy J. « Development of a microchannel plate image intensifier for an astronomical photon-counting detector ». Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391940.
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Panina, Ekaterina. « Design and characterisation of SPAD based CMOS analog pixels for photon-counting applications ». Doctoral thesis, Università degli studi di Trento, 2014. https://hdl.handle.net/11572/368962.
Texte intégralRésumé :
Recent advancements in biomedical research and imaging applications have ignited an intense interest in single-photon detection. Along with single-photon resolution, nanosecond or sub-nanosecond timing resolution and high sensitivity of the device must be achieved at the same time. Single- Photon Avalanche Diodes (SPADs) have proved their prospectives in terms of shot-noise limited operation, excellent timing resolution and wide spec- tral range. Nonetheless, the performance of recently presented SPAD based arrays has an issue of low detection efficiency by reason of the area on the substrate occupied by additional processing electronics.
This dissertation presents the design and experimental characteriza- tion of a few compact analog readout circuits for SPAD based arrays. Tar- geting the applications where the spatial resolution is the key requirement, the work is focused on the circuit compactness, that is, pixel fill factor re- finement. Consisting of only a few transistors, the proposed structures are remarkable for a small area occupation. This significant advancement has been achieved with the analog implementation of the additional circuitry instead of standard digital approach. Along with the compactness, the dis- tinguishing features of the circuits are low power consumption, low output non-linearity and pixel-to-pixel non-uniformity. In addition, experimental results on a time-gated operation have proved feasibility of a sub-nanosecond time window.
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Panina, Ekaterina. « Design and characterisation of SPAD based CMOS analog pixels for photon-counting applications ». Doctoral thesis, University of Trento, 2014. http://eprints-phd.biblio.unitn.it/1155/1/PhD-Thesis.pdf.
Texte intégralRésumé :
Recent advancements in biomedical research and imaging applications have ignited an intense interest in single-photon detection. Along with single-photon resolution, nanosecond or sub-nanosecond timing resolution and high sensitivity of the device must be achieved at the same time. Single- Photon Avalanche Diodes (SPADs) have proved their prospectives in terms of shot-noise limited operation, excellent timing resolution and wide spec- tral range. Nonetheless, the performance of recently presented SPAD based arrays has an issue of low detection efficiency by reason of the area on the substrate occupied by additional processing electronics.
This dissertation presents the design and experimental characteriza- tion of a few compact analog readout circuits for SPAD based arrays. Tar- geting the applications where the spatial resolution is the key requirement, the work is focused on the circuit compactness, that is, pixel fill factor re- finement. Consisting of only a few transistors, the proposed structures are remarkable for a small area occupation. This significant advancement has been achieved with the analog implementation of the additional circuitry instead of standard digital approach. Along with the compactness, the dis- tinguishing features of the circuits are low power consumption, low output non-linearity and pixel-to-pixel non-uniformity. In addition, experimental results on a time-gated operation have proved feasibility of a sub-nanosecond time window.
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Tyndall, David. « CMOS system for high throughput fluorescence lifetime sensing using time correlated single photon counting ». Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/12238.
Texte intégralRésumé :
Fluorescence lifetime sensing using time correlated single photon counting (TCSPC) is a key analytical tool for molecular and cell biology research, medical diagnosis and pharmacological development. However, commercially available TCSPC equipment is bulky, expensive and power hungry, typically requiring iterative software post-processing to calculate the fluorescence lifetime. Furthermore, the technique is restrictively slow due to a low photon throughput limit which is necessary to avoid distortions caused by TCSPC pile-up. An investigation into CMOS compatible multimodule architectures to miniaturise the standard TCSPC set up, allow an increase in photon throughput by overcoming the TCSPC pile-up limit, and provide fluorescence lifetime calculations in real-time is presented. The investigation verifies the operation of the architectures and leads to the selection of optimal parameters for the number of detectors and timing channels required to overcome the TCSPC pile-up limit by at least an order of magnitude. The parameters are used to implement a low power miniaturised sensor in a 130 nm CMOS process, combining single photon detection, multiple channel timing and embedded pre-processing of the fluorescence lifetime, all within a silicon area of < 2 mm2. Single photon detection is achieved using an array of single photon avalanche diodes (SPADs) arranged in a digital silicon photomultiplier (SiPM) architecture with a 10 % fill-factor and a compressed 250 ps output pulse, which provides a photon throughput of > 700 MHz. An array of time-interleaved time-to-digital converters (TI-TDCs) with 50 ps resolution and no processing dead-time records up to eight photon events during each excitation period, significantly reducing the effect of TCSPC pile-up. The TCSPC data is then processed using an embedded centre-of-mass method (CMM) pre-calculation to produce single exponential fluorescence lifetime estimations in real-time. The combination of high photon throughput and real-time calculation enables advances in applications such as fluorescence lifetime imaging microscopy (FLIM) and time domain fluorescence lifetime activated cell sorting. To demonstrate this, the device is validated in practical bulk sample fluorescence lifetime, FLIM and simulated flow based experiments. Photon throughputs in excess of the excitation frequency are demonstrated for a range of organic and inorganic fluorophores for minimal error in lifetime calculation by CMM (< 5 %).
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Barter, Laura Mary Claire. « Energy and electron transfer in photosystem two studied by time resolved single photon counting ». Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248222.
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Harkins, Ross Douglas. « A multiple wavelength time-of-flight sensor, based on time-correlated single-photon counting ». Thesis, Heriot-Watt University, 2005. http://hdl.handle.net/10399/199.
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CALLIARI, FELIPE. « AUTOMATIC HIGH-DYNAMIC AND HIGH-RESOLUTION PHOTON COUNTING OTDR FOR OPTICAL FIBER NETWORK MONITORING ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=31668@1.
Texte intégralRésumé :
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Neste trabalho é apresentado o desenvolvimento de uma estrutura automatizada para o monitoramento de fibras ópticas. Esta estrura consite em dois tipos de reflectômetros ópticos por contagem de fótons no domínio do tempo e um filtro de tendências que é utilizado para detectar as falhas em uma fibra óptica de forma automatizada. O primeiro OTDR por contagem de fótons apresenta uma faixa dinâmica de 32 dB com resolução espacial de 6 m, já o segundo OTDR apresenta uma faixa dinâmica de 14 dB e uma resolução de 3 cm. Foi demonstrada a sua capacidade de detectar falhas automaticamente em um enlace óptica e de sintonização no monitoramento de redes passivas WDM.
In this work the development of an automated structure for the monitoring of optical fibers is presented. This structure consists of two types of Photon Counting Optical Time Domain Reflectometers and a trend filter that is used to detect fiber faults in an automated way. The first Photon Counting OTDR has a 32 dB dynamic range with spatial resolution of 6 m, while the second OTDR has a 14 dB dynamic range and a resolution of 3 cm. Its ability to automatically detect faults in an optical fiber link and tunability for monitoring of optical WDM networks has been demonstrated.