29 research outputs found

    Bent beamlets - efficient tool in image coding

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    In recent years spectral methods, especially wavelets theory, have gained wide popularity in digital image processing because they allow for very sparse and efficient image coding. Although they are good in analyzing one dimensional signal, they cannot properly catch line discontinuities, so they are often present in two dimensional signals, that is in images. To avoid these problems the theory of geometrical wavelets has been created in recent years, which have all advantages of wavelets and moreover, allows to catch line discontinuities properly. Beamlets are those of a wide spectrum of the new theory of geometrical wavelets. They are successfully used in many areas of digital image processing, particularly in multiresolution image coding. In the paper presents the improvement of the beamlets theory, which allows to code images in a more efficient way than in the case of the classical beamlets. Also in other areas of image processing this improved theory can be successfully used. The experiments performed on a wide spectrum of test images have confirmed great usefulness of the improved - bent beamlets. In the paper the examples of isobar image coding are also presented

    Optimization of an SRF Gun for High Bunch Charge Applications at ELBE

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    As a cutting-edge technology for photoinjectors, SRF guns are expected to provide CW electron beams with high bunch charge and low emittance, which is critical to the development of future FELs, ERLs and 4th/5th generation light sources. However, existing research has not explored the full potential of SRF guns as predicted by theory. Currently, the research activities at ELBE focus on solving technological challenges of a 3.5 cell SRF gun as well as applying it to high-bunch-charge experiments. This thesis aims to optimize the ELBE SRF gun and the relevant beam transport for future high-bunch-charge applications at pELBE, nELBE, TELBE and CBS experimental stations. Chapter 1 describes the demands of these applications on the SRF gun in detail. Chapter 2 outlines the development of a simulation tool based on ASTRA and Elegant, followed by the optimized gun parameters and the beam transport for the four experimental stations. Chapter 3 introduces beam diagnostic methods and data processing applied in this thesis. Chapter 4 presents results of experiments, including the pulse length measurement of the UV laser for generating electrons from the photcathode, the commissioning of ELBE SRF Gun II, a verification experiment on the LSC effect conducted at PITZ and a beam transport experiment with the bunch charge of 200 pC. Simulation results have determined the effect of each SRF gun parameter on the beam quality and have provided optimized settings according to the requirements in Chapter 1. Experimentally, the LSC effect was confirmed at PITZ, in agreement with simulations which indicated that LSC significantly influences beam quality. The performance of ELBE SRF Gun II was improved and a beam with a bunch charge of 200 pC and an emittance of 7.7 ÎĽm from ELBE SRF Gun II has been transported through ELBE without visible beam loss. The development of the simulation tool and beam diagnostics will serve further research at ELBE. Results of both simulations and experiments enrich the understanding of the existing SRF gun as well as the ELBE beamline and will guide continuing improvements. Already, ELBE SRF Gun II can deliver twice the bunch charge and lower emittance compared to the thermionic injector routinely used for ELBE. Ongoing modifications and development of the gun-cavity and photocathodes are expected to provide still further improvements. Progress on high-bunch-charge experiments at ELBE can be expected by applying the SRF gun

    Intensity modulated radiation therapy and arc therapy: validation and evolution as applied to tumours of the head and neck, abdominal and pelvic regions

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    Intensiteitsgemoduleerde radiotherapie (IMRT) laat een betere controle over de dosisdistributie (DD) toe dan meer conventionele bestralingstechnieken. Zo is het met IMRT mogelijk om concave DDs te bereiken en om de risico-organen conformeel uit te sparen. IMRT werd in het UZG klinisch toegepast voor een hele waaier van tumorlocalisaties. De toepassing van IMRT voor de bestraling van hoofd- en halstumoren (HHT) vormt het onderwerp van het eerste deel van deze thesis. De planningsstrategie voor herbestralingen en bestraling van HHT, uitgaande van de keel en de mondholte wordt beschreven, evenals de eerste klinische resultaten hiervan. IMRT voor tumoren van de neus(bij)holten leidt tot minstens even goede lokale controle (LC) en overleving als conventionele bestralingstechnieken, en dit zonder stralingsgeïnduceerde blindheid. IMRT leidt dus tot een gunstiger toxiciteitprofiel maar heeft nog geen bewijs kunnen leveren van een gunstig effect op LC of overleving. De meeste hervallen van HHT worden gezien in het gebied dat tot een hoge dosis bestraald werd, wat erop wijst dat deze “hoge dosis” niet volstaat om alle clonogene tumorcellen uit te schakelen. We startten een studie op, om de mogelijkheid van dosisescalatie op geleide van biologische beeldvorming uit te testen. Naast de toepassing en klinische validatie van IMRT bestond het werk in het kader van deze thesis ook uit de ontwikkeling en het klinisch opstarten van intensiteitgemoduleerde arc therapie (IMAT). IMAT is een rotationele vorm van IMRT (d.w.z. de gantry draait rond tijdens de bestraling), waarbij de modulatie van de intensiteit bereikt wordt door overlappende arcs. IMAT heeft enkele duidelijke voordelen ten opzichte van IMRT in bepaalde situaties. Als het doelvolume concaaf rond een risico-orgaan ligt met een grote diameter, biedt IMAT eigenlijk een oneindig aantal bundelrichtingen aan. Een planningsstrategie voor IMAT werd ontwikkeld, en type-oplossingen voor totaal abdominale bestraling en rectumbestraling werden onderzocht en klinisch toegepast

    Evaluation of a desktop computed radiography system for IMRT dosimetry

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    Different techniques have been developed and used to evaluate dose distribution calculation accuracy and dose delivery reproducibility as a part of patient-specific IMRT QA – e.q. film dosimetry, ionization chambers, and diode arrays. To verify that the calculated dose distribution is delivered accurately during treatment, film dosimetry is usually used. The accuracy and reproducibility of film optical density as an indicator of dose is influenced by several variables, including the chemical processing and scanning conditions. This study investigates the possibility to use a desktop computed radiography (CR) system for patient-specific intensity modulated radiation therapy (IMRT) quality assurance (QA). A study was done at Mary Bird Perkins Cancer Center, Baton Rouge, LA; where phantom IMRT plans are calculated using an ADAC Pinnacle3 treatment planning system. A Kodak ACR-2000i system is used for the study together with Kodak flexible phosphor screens (plates). In this study, 778 CR plate exposures were done. Several tests were performed including evaluation of the CR plate response dependency when exposed to changes in either setup or scan conditions. Calibration curves were generated for three different energies: 4 MV, 6 MV and 10 MV. Using these calibration curves, the CR plates’ response and behavior as an IMRT tool was analyzed using 10 different patients’ IMRT plans for each energy with approximately 7 fields per patient. Analysis of film was done with commercial IMRT analysis software. Analysis of CR plate data was done in IDL (Research Systems, Inc.), with programs written in house, and included several separate algorithms including automatic image registration. This algorithm uses the Fourier-Mellin transform for automatic image registration. It was found that CR plates showed generally good agreement with the planned values with some significant over-response in the low dose regions, which can be reduced by filtration and improved calibration curves. In view of the results presented, a CR system stands as a potentially fast and practical tool for IMRT patient-specific treatment QA

    Adaptive techniques with polynomial models for segmentation, approximation and analysis of faces in video sequences

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    Conference on Binary Optics: An Opportunity for Technical Exchange

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    The papers herein were presented at the Conference on Binary Optics held in Huntsville, AL, February 23-25, 1993. The papers were presented according to subject as follows: modeling and design, fabrication, and applications. Invited papers and tutorial viewgraphs presented on these subjects are included

    Index to 1983 NASA Tech Briefs, volume 8, numbers 1-4

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    Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1983 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

    Optical Focusing and Imaging through Scattering Media

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    Optical techniques, which have been widely used in various fields including bio-medicine, remote sensing, astronomy, and industrial production, play an important role in modern life. Optical focusing and imaging, which correspond to the basic methods of utilizing light, are key to the implementation of optical techniques. In free space or a nearly transparent medium, optical imaging and focusing can be easily realized by using conventional optical elements, such as lenses and mirrors, due to the ballistic propagation of light in these media. However, in scattering media like biological tissue and fog, refractive index inhomogeneities cause diffusive propagation of light that increases with depth, which restricts the use of optical methods in thick, scattering media. Generally speaking, scattering media poses three challenges to optical focusing and imaging: wavefront aberrations, glare, and decorrelation. Wavefront aberrations can randomize light traveling through a scattering medium, disrupt the formation of focus, and break the conjugate relation in imaging. Glare caused by backscattering will largely impair the visibility of imaging, and decorrelation in dynamic media requires systems that counter the effect of scattering to operate faster than the decorrelation time. In this thesis, we explored solutions to the problem of scattering from different aspects. We presented Time Reversal by Analysis of Changing wavefronts from Kinetic targets (TRACK) technique to realize noninvasive optical focusing through a scattering medium. We showed that by taking the difference between time-varying scattering fields caused by a moving object and applying optical phase conjugation, light can be focused back to the location previously occupied by the object. To tackle the decorrelation of living tissue, we built up a fast digital optical phase conjugation (DOPC) system based on FPGA and DMD, which has a response time of 5.3 ms and was the fastest DOPC system in the world before 2017. We demonstrated that the system is fast enough to focus light through 2.3mm-thick living mouse skin. As for glare, inspired by noise canceling headphones, we invented an optical analogue termed coherence gated negation (CGN) technique. CGN can optically cancel out the glare in an active illumination imaging scenario to realize imaging through scattering media, like fog. In the experiment, we suppressed the glare by an order of magnitude and allowed improved imaging of a weak target. Finally, we demonstrated a method to image a moving target through scattering media noninvasively. Its principle roots are in the speckle-correlation-based imaging (SCI) invented by Ori Katz. We improved the technique and extended its application to bright field imaging of a moving target.</p

    NASA Tech Briefs, Winter 1983

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    Topics include: NASA TU Services: Technology Utilization services that can assist you in learning about and applying NASA technology. New Product Ideas: A summary of selected innovations of value to manufacturers for the development of new products; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Life Sciences; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences
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