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On the bias in measurement of the asymmetry of Poisson flows

JOURNAL OF INSTRUMENTATION 2012年第05期7卷 P05001-P05001页

作者： Bityukov, S. I. Krasnikov, N. V. Smirnova, V. V. Inst High Energy Phys Protvino 142281 Russia Inst Nucl Res RAS Moscow 117312 Russia

The asymmetry between rates of two event flows is considered. The presence of a bias between the observed asymmetry and the true asymmetry is shown. Monte Carlo experiments confirm the presence of the bias. An approxi... 详细信息

关键词： data processing methods Analysis and statistical methods

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A development environment for visual physics analysis

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JOURNAL OF INSTRUMENTATION 2012年第08期7卷 T08005-T08005页

作者： Bretz, H. -P. Brodski, M. Erdmann, M. Fischer, R. Hinzmann, A. Klimkovich, T. Klingebiel, D. Komm, M. Lingemann, J. Mueller, G. Muenzer, T. Rieger, M. Steggemann, J. Winchen, T. Rhein Westfal TH Aachen Phys Inst A 3 D-52062 Aachen Germany

The Visual Physics Analysis (VISPA) project integrates different aspects of physics analyses into a graphical development environment. It addresses the typical development cycle of (re-)designing, executing and verifying an analysis. The project provides an extendable plug-in mechanism and includes plug-ins for designing the analysis flow, for running the analysis on batch systems, and for browsing the data content. The corresponding plug-ins are based on an object-oriented toolkit for modular data analysis. We introduce the main concepts of the project, describe the technical realization and demonstrate the functionality in example applications.

关键词： data processing methods Software architectures (event data models, frameworks and databases) Analysis and statistical methods

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Improving the spectral resolution of a highly pixelated detector by applying a pixel-by-pixel energy calibration for investigating the spectral properties of the anode heel effect

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JOURNAL OF INSTRUMENTATION 2012年第07期7卷 P07011-P07011页

作者： Sievers, P. Klammer, J. Michel, T. Hupe, O. Anton, G. Phys Tech Bundesanstalt D-38116 Braunschweig Germany Univ Erlangen Nurnberg ECAP D-91058 Erlangen Germany

The energy deposition spectrum measured with highly pixelated photon-counting pixel detectors with a semiconductor sensor layer (e. g. silicon) differs significantly from the impinging X-ray spectrum. This is the main disadvantage compared to commonly known X-ray spectrometers, e. g. high purity Germanium (hpGe) detector. On the other hand, those hpGe-detectors have a lack of spatial resolution and can not be used for energy-resolved imaging. In case of measurements with highly pixelated detectors, a set of monoenergetic detector response functions is needed for the deconvolution of the measured distribution into the impinging spectrum. We have investigated the possibility of applying a pixel-by-pixel calibration on a highly pixelated detector for gaining a higher energy resolution and for lowering the minimal flux needed for the deconvolution. As a result it is now possible to utilize small ROIs of the pixel matrix for the deconvolution. With this analysis method the detector enables spectral X-ray imaging of high photon rates. This is in particular shown for the angular dependency of the anode heel effect on the emitted spectrum.

关键词： data processing methods X-ray detectors Spectrometers X-ray generators and sources

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TUnfold, an algorithm for correcting migration effects in high energy physics

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JOURNAL OF INSTRUMENTATION 2012年第10期7卷 T10003-T10003页

作者： Schmitt, S. DESY D-22607 Hamburg Germany

TUnfold is a tool for correcting migration and background effects in high energy physics for multi-dimensional distributions. It is based on a least square fit with Tikhonov regularisation and an optional area constraint. For determining the strength of the regularisation parameter, the L-curve method and scans of global correlation coefficients are implemented. The algorithm supports background subtraction and the propagation of statistical and systematic uncertainties, in particular those originating from limited knowledge of the response matrix. The program is interfaced to the ROOT analysis framework.

关键词： data processing methods Analysis and statistical methods

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Contrast optimization in X-ray radiography with single photon counting imagers of Medipix type

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JOURNAL OF INSTRUMENTATION 2012年第12期7卷 C12011-C12011页

作者： Jandejsek, I. Dammer, J. Jakubek, J. Vavrik, D. Zemlicka, J. Czech Tech Univ Inst Expt & Appl Phys Prague 12800 2 Czech Republic Acad Sci Czech Republ Vvi Inst Theoret & Appl Mech Prague 19000 9 Czech Republic Charles Univ Prague Fac Med 1 Prague 10000 2 Czech Republic

Systematical measurement and optimization of the image contrast in the terms of the signal to noise ratio (SNR) reached by two detector systems Medipix2 (Si sensor) and Flat Panel (Scintillator + CMOS) is the aim of this work. The measurement is carried out with micro-focus X-ray source and aluminum step phantom specimen of various thicknesses. The SNR is computed from measured image data for various combination of aluminum thicknesses and in dependence on tube voltage and acquisition time. On the basis of the results, the comparison of two detector systems is done and the illustrative SNR optimization process for a hypothetical and real samples is demonstrated.

关键词： X-ray detectors X-ray radiography and digital radiography (DR) data processing methods Inspection with x-rays

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Image recovery by removing stochastic artefacts identified as local asymmetries

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JOURNAL OF INSTRUMENTATION 2012年第04期7卷 C04018-C04018页

作者： Osterloh, K. Buecherl, T. Zscherpel, U. Ewert, U. BAM Fed Inst Mat Res & Testing D-12205 Berlin Germany Tech Univ Munich Radiochem Munchen RCM D-85748 Garching Germany

Stochastic artefacts are frequently encountered in digital radiography and tomography with neutrons. Most obviously, they are caused by ubiquitous scattered radiation hitting the CCD-sensor. They appear as scattered dots and, at higher frequency of occurrence, they may obscure the image. Some of these dotted interferences vary with time, however, a large portion of them remains persistent so the problem cannot be resolved by collecting stacks of images and to merge them to a median image. The situation becomes even worse in computed tomography (CT) where each artefact causes a circular pattern in the reconstructed plane. Therefore, these stochastic artefacts have to be removed completely and automatically while leaving the original image content untouched. A simplified image acquisition and artefact removal tool was developed at BAM and is available to interested users. Furthermore, an algorithm complying with all the requirements mentioned above was developed that reliably removes artefacts that could even exceed the size of a single pixel without affecting other parts of the image. It consists of an iterative two-step algorithm adjusting pixel values within a 3 x 3 matrix inside of a 5 x 5 kernel and the centre pixel only within a 3 x 3 kernel, resp. It has been applied to thousands of images obtained from the NECTAR facility at the FRM II in Garching, Germany, without any need of a visual control. In essence, the procedure consists of identifying and tackling asymmetric intensity distributions locally with recording each treatment of a pixel. Searching for the local asymmetry with subsequent correction rather than replacing individually identified pixels constitutes the basic idea of the algorithm. The efficiency of the proposed algorithm is demonstrated with a severely spoiled example of neutron radiography and tomography as compared with median filtering, the most convenient alternative approach by visual check, histogram and power spectra analysis.

关键词： Image filtering data processing methods Pattern recognition, cluster finding, calibration and fitting methods

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Improving the spatial resolution of a soft X-ray Charge Coupled Device used for Resonant Inelastic X-ray Scattering

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JOURNAL OF INSTRUMENTATION 2011年第11期6卷

作者： Soman, M. R. Hall, D. J. Tutt, J. H. Murray, N. J. Holland, A. D. Schmitt, T. Raabe, J. Schmitt, B. Open Univ Ctr Elect Imaging E2V Milton Keynes MK7 6AA Bucks England Paul Scherrer Inst CH-5232 Villigen Switzerland

The Super Advanced X-ray Emission Spectrometer (SAXES) at the Advanced Resonant Scattering (ADRESS) beamline of the Swiss Light Source is a high-resolution X-ray spectrometer used as an end station for Resonant Inelastic X-ray Scattering from 400 eV to 1600 eV. Through the dispersion of photons across a CCD, the energy of scattered photons may be determined by their detected spatial position. The limiting factor of the energy resolution is currently the spatial resolution achieved with the CCD, reported at 24 mu m FWHM. For this energy range the electron clouds are formed by interactions in the 'field free' region of the back-illuminated CCD. These clouds diffuse in all directions whilst being attracted to the electrodes, leading to events that are made up of signals in multiple pixels. The spreading of the charge allows centroiding techniques to be used to improve the CCD spatial resolution and therefore improve the energy resolution of SAXES. The PolLux microscopy beamline at the SLS produces an X-ray beam with a diameter of 20 nm. The images produced from scanning the narrow beam across CCD pixels (13.5 x 13.5 mu m(2)) can aid in the production of event recognition algorithms, allowing the matching of event profiles to photon interactions in a specific region of a pixel. Through the use of this information software analysis can be refined with the aim of improving the energy resolution.

关键词： data processing methods Solid state detectors X-ray detectors Spectrometers

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Small Dosimeter based on Timepix device for International Space Station

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JOURNAL OF INSTRUMENTATION 2011年第12期6卷 C12037-C12037页

作者： Turecek, D. Pinsky, L. Jakubek, J. Vykydal, Z. Stoffle, N. Pospisil, S. Czech Tech Univ Inst Expt & Appl Phys Prague 12800 Czech Republic Univ Houston Houston TX 77004 USA

The radiation environment in space is different, more complex and more intense than on Earth. Conventional devices and detection methods used nowadays do not allow to discriminate single particle types and the energy of the single particles. The Timepix detector is a position sensitive pixelated detector developed at CERN in a frame of the Medipix collaboration that provides capability to visualize tracks and measure energy of single particles. This information can be used for sorting the particles into different categories. It is possible to distinguish light charged particles such as electrons or heavy charged particles such as ions. Moreover, the Linear Energy Transfer ( LET) for charged particles can be determined. Each category is assigned a quality factor corresponding to the energy a particle would deposit in the human tissue. By summing the dose of all particles an estimate of the dose rate can be calculated. For space dosimetry purposes a miniature device with the Timepix detector and a custom made integrated USB based readout interface has been constructed. The entire device has dimensions of a USB flash memory stick. The whole compact device is connected to a control PC and is operated continuously. The PC runs a software that controls data acquisition, adjusts the acquisition time adaptively according to the particle rate, analyzes the particle tracks, evaluates the deposited energy and the LET and visualizes in a simple display the estimated dose rate. The performance of the device will be tested during a mission on International Space Station planned towards the beginning of year 2012.

关键词： data processing methods Dosimetry concepts and apparatus Detector control systems (detector and experiment monitoring and slow-control systems, architecture, hardware, algorithms, databases)

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X-ray color imaging with 3D sensitive voxel detector

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JOURNAL OF INSTRUMENTATION 2011年第12期6卷 C12014-C12014页

作者： Soukup, P. Jakubek, J. Jandejsek, I. Zemlicka, J. Czech Tech Univ Inst Expt & Appl Phys Prague 12800 2 Czech Republic

X-ray imaging is today widely used in a broad range of applications. Nevertheless some limitations are represented by the inability to distinguish between a thick layer of low Z material and a thin layer of high Z material, and by the beam hardening, where the incident X-ray spectrum is modified as the beam traverses the sample. Such effects cause problems in many applications (e.g. CT reconstruction) generating artifacts and worsening the spatial resolution. This work presents a new technique allowing spectral sensitivity using a new 3D voxel detector based on the Timepix pixel detector. The device is designed as a layered stack of several Timepix sensors. The readout chip is thinned down to reduce the amount of insensitive absorbing material. Every single layers in the stack act as a filter, i.e. each stack layer visualizes a different part of the spectrum attenuated by the object giving further information about the object composition. The comparison of attenuation levels observed in different detector layers can be used to estimate the extent of the beam hardening effect in the imaged object and thus point out differences in the material composition.

关键词： data processing methods Inspection with x-rays

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Image processing for X-ray transmission radiography with 3D voxel detector

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JOURNAL OF INSTRUMENTATION 2011年第12期6卷 C12061-C12061页

作者： Jandejsek, I. Soukup, P. Jakubek, J. Czech Tech Univ Inst Expt & Appl Phys CZ-12800 Prague 2 Czech Republic

Presented paper deals with the image processing for the new 3D voxel detector. The detector is mainly intended for particle tracking applications, but it has also advantages in conventional X-ray transmission radiography. Imaging with such device brings benefits such as higher detection efficiency, presence of directional information and mapping of beam-hardening effects. To get these additional imaging possibilities, the raw image data acquired by the voxel detector have to be processed by a method of image matching based on the Lucas-Kanade algorithm in conjunction with a cross-correlation method. The main result of the image data processing is an assembled image ready for further analysis. The secondary outcome is the information about the geometry of the imaging setup (i.e. measured position of the detector relative to the X-ray source). Results together with evaluation of the techniques are demonstrated on images of real samples.

关键词： Image filtering data processing methods Image reconstruction in medical imaging Pattern recognition, cluster finding, calibration and fitting methods

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