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[en] A digital x-ray mammography is a modern method for the early detection of breast cancer. The quality of a mammography image depends on various factors, the detector structure and performance being of primary importance. The aim of this work was to develop an analytical model simulating the imaging performance of a new commercially available digital mammography detector. This was achieved within the framework of the linear cascaded systems (LCS) theory. System analysis has allowed the estimation of important image quality metrics such as the Modulation Transfer Function (MTF), the Noise Power Spectrum (NPS) and the Detective Quantum Efficiency (DQE). The detector was an indirect detection system consisting of a large area, 100μm thick, CsI:TI scintillator coupled to an active matrix array of amorphous silicon (a-Si:H) photodiodes combined with thin film transistors (TFT). Pixel size was 100μm, while the active pixel dimension was 70μm. MTF and DQE data were calculated for air kerma conditions of 25, 53, 67 μGy using a 28 kVp Mo-Mo x-ray spectrum. The theoretical results were compared with published experimental data. The deviation between the theoretical and experimental MTF curves was less than 4%, while the DQE differences were found at an acceptable level. The model was also used to estimate system's capability to detect low contrast objects in the breast. It was estimated that, in the breast gland, low contrast structures larger than 1.4mm can be adequately identified by the above system.
[en] Antiprotons whose potential in clinical applications has not yet been fully studied and explored, interact in a way similar to the widely used protons. The great advantage of antiprotons over protons is that at the end of their path annihilate and release about 1.88GeV more energy. Although many particles are produced by annihilation most of them escape from the target. Detecting a portion of these particles during patient's irradiation would offer the possibility to monitor the beam in the target in real time. In the current work we investigate the feasibility of real time imaging during radiotherapy by using antiproton beam. In this study a prostate case is simulated using one field and given a typical dose fraction of 2Gy to the target. Monte Carlo code is used to calculate the energy spectrum of the most prominent particles that escape from the target which could be detected outside the patient, as well as the degree of scattering of these particles, as an indication of merit for their use in order to produce an image which represents the absorption of the beam in the target. Results based on these criteria suggest that real time imaging is possible by detecting either charged pions or photons which mainly come from π0 decays or e+e- annihilation.
[en] Microwave radiometry is a measurement technique which detects natural-thermal radiation emitted by matter. The human brain having certain temperature and specific electromagnetic properties emits chaotic radiation throughout the whole electromagnetic spectrum. A novel Microwave Radiometry Imaging System (MiRaIS) comprising an ellipsoidal conductive wall cavity and sensitive radiometric receivers, operating at low microwave frequencies (1-4GHz), has been used the past four years in various experiments to assess its value as a potential intracranial imaging device. With this view, current research aims at the improvement of the system's focusing properties using matching layers made of dielectric and left handed materials that are placed around a double layered human head model. Another approach tested, included filling of the whole ellipsoidal with a lossless dielectric material in conjunction with reduction of the ellipsoid's volume. The results show better focusing properties in the brain areas of interest and improvement of the system's spatial resolution. Future research including mainly phantom and human experiments implementing the above ideas will illustrate the value of the present simulation study.
[en] Waveform acquisition and presentation forms the heart of many measurement systems. Particularly, data acquisition and presentation of repeating complex signals like sine sweep and frequency-modulated signals introduces the challenge of waveform time period estimation and live waveform presentation. This paper presents an intelligent technique, for waveform period estimation of both the complex and simple waveforms, based on the normalized auto-correlation method. The proposed technique is demonstrated using LabVIEW based intensive simulations on several simple and complex waveforms. Implementation of the technique is successfully demonstrated using LabVIEW based virtual instrumentation. Sine sweep vibration waveforms are successfully presented and measured for electrodynamic shaker system generated vibrations. The proposed method is also suitable for digital storage oscilloscope (DSO) triggering, for complex signals acquisition and presentation. This intelligence can be embodied into the DSO, making it an intelligent measurement system, catering wide varieties of the waveforms. The proposed technique, simulation results, robustness study and implementation results are presented in this paper.
[en] In this paper we study several fixed step and adaptive Runge-Kutta methods suitable for transporting track parameters through an inhomogeneous magnetic field. Moreover, we present a new adaptive Runge-Kutta-Nystroem method which estimates the local error of the extrapolation without introducing extra stages to the original Runge-Kutta-Nystroem method. Furthermore, these methods are compared for propagation accuracy and computing cost efficiency in the simultaneous track and error propagation (STEP) algorithm of the common ATLAS tracking software. The tests show the new adaptive Runge-Kutta-Nystroem method to be the most computing cost efficient.
[en] Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noise and a small number of malfunctioning calorimeter channels. Algorithms have been developed to identify and address these problems in the data. The methods have been tested on cosmic ray muon data, calorimeter noise data, and single beam data collected with CMS in 2008. The noise rejection algorithms can be applied to LHC collision data at the trigger level or in the offline analysis. The application of the algorithms at the trigger level is shown to remove 90% of noise events with fake missing transverse energy above 100 GeV, which is sufficient for the CMS physics trigger operation.
[en] This paper describes the calibration procedure for the drift tubes of the CMS barrel muon system and reports the main results obtained with data collected during a high statistics cosmic ray data-taking period. The main goal of the calibration is to determine, for each drift cell, the minimum time delay for signals relative to the trigger, accounting for the drift velocity within the cell. The accuracy of the calibration procedure is influenced by the random arrival time of the cosmic muons relative to the LHC clock cycle. A more refined analysis of the drift velocity was performed during the offline reconstruction phase, which takes into account this feature of cosmic ray events.
[en] In this paper the design criteria, construction and final performance of the silicon micro-strip modules installed in the LHCf experiment are described. LHCf is an experiment currently placed at CERN in the LHC tunnel. It consists of two small calorimeters each one placed 140 metres away from the ATLAS interaction point. Their purpose is to study very forward production of neutral particles in proton-proton collisions. The silicon modules are installed in one of the two calorimeters and provide precision information on the shower transverse profile.
[en] The Low Frequency Instrument (LFI) is an array of cryogenically cooled radiometers on board the Planck satellite, designed to measure the temperature and polarization anisotropies of the cosmic microwave background (CMB) at 30, 44 and 70 GHz. The thermal requirements of the LFI, and in particular the stringent limits to acceptable thermal fluctuations in the 20 K focal plane, are a critical element to achieve the instrument scientific performance. Thermal tests were carried out as part of the on-ground calibration campaign at various stages of instrument integration. In this paper we describe the results and analysis of the tests on the LFI flight model (FM) performed at Thales Laboratories in Milan (Italy) during 2006, with the purpose of experimentally sampling the thermal transfer functions and consequently validating the numerical thermal model describing the dynamic response of the LFI focal plane. This model has been used extensively to assess the ability of LFI to achieve its scientific goals: its validation is therefore extremely important in the context of the Planck mission. Our analysis shows that the measured thermal properties of the instrument show a thermal damping level better than predicted, therefore further reducing the expected systematic effect induced in the LFI maps. We then propose an explanation of the increased damping in terms of non-ideal thermal contacts.
[en] This paper describes the impact of the Planck Low Frequency Instrument front end physical temperature fluctuations on the output signal. The origin of thermal instabilities in the instrument are discussed, and an analytical model of their propagation and impact on the receivers signal is described. The experimental test setup dedicated to evaluate these effects during the instrument ground calibration is reported together with data analysis methods. Finally, main results obtained are discussed and compared to the requirements.