共查询到20条相似文献,搜索用时 15 毫秒
1.
Park SJ Leslie Rogers W Huh S Kagan H Honscheid K Burdette D Chesi E Lacasta C Llosa G Mikuz M Studen A Weilhammer P Clinthorne NH 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2007,570(3):543-555
A very high-resolution small animal positron emission tomograph (PET), which can achieve sub-millimeter spatial resolution, is being developed using silicon pad detectors. The prototype PET for a single slice instrument consists of two 1 mm thick silicon pad detectors, each containing a 32×16 array of 1.4×1.4 mm pads readout with four VATAGP3 chips which have 128 channels low-noise self-triggering ASIC in each chip, coincidence units, a source turntable and tungsten slice collimator. The silicon detectors were located edgewise on opposite sides of a 4 cm field-of-view to maximize efficiency. Energy resolution is dominated by electronic noise, which is 0.98% (1.38 keV) FWHM at 140.5 keV. Coincidence timing resolution is 82.1 ns FWHM and coincidence efficiency was measured to be 1.04×10−3% from two silicon detectors with annihilation photons of 18F source. Image data were acquired and reconstructed using conventional 2-D filtered-back projection (FBP) and a maximum likelihood expectation maximization (ML-EM) method. Image resolution of approximately 1.45 mm FWHM is obtained from 1-D profile of 1.1 mm diameter 18F line source image. Even better resolution can be obtained with smaller detector element sizes. While many challenges remain in scaling up the instrument to useful efficiency including densely packed detectors and significantly improved timing resolution, performance of the test setup in terms of easily achieving sub-millimeter resolution is compelling. 相似文献
2.
E. A. Samoilin 《Measurement Techniques》2008,51(7):718-723
A method is proposed for estimating the coordinates of an object invariant with respect to localization and size on digital
images on the basis of the closeness function for nested arrays of images of the object and the standard.
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Translated from Izmeritel’naya Tekhnika, No. 7, pp. 15–19, July, 2008. 相似文献
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P. Wicek W. Dbrowski 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2007,580(3):1355-1362
This paper describes an experimental investigation of the energy and spatial response of silicon strip detectors used for X-ray measurements. The measurements of single strip amplitude distributions have been performed for a p+–n silicon strip detector irradiated with X-rays for different detector bias voltages and for two measurements geometries (with the detector irradiated from either the strip side or from the ohmic contact side). The measured amplitude distributions have been compared with those obtained from simulations using the developed simulation package. The spatial response of the detector has been measured by scanning an edge across the strips and measuring the corresponding strip count rate. The measured spatial response has been compared with that obtained from simulations. 相似文献
4.
Andre Kyme Steven Meikle Clive Baldock Roger Fulton 《Journal of the Royal Society Interface》2012,9(76):3094-3107
Positron emission tomography (PET) is an important in vivo molecular imaging technique for translational research. Imaging unanaesthetized rats using motion-compensated PET avoids the confounding impact of anaesthetic drugs and enables animals to be imaged during normal or evoked behaviour. However, there is little published data on the nature of rat head motion to inform the design of suitable marker-based motion-tracking set-ups for brain imaging—specifically, set-ups that afford close to uninterrupted tracking. We performed a systematic study of rat head motion parameters for unanaesthetized tube-bound and freely moving rats with a view to designing suitable motion-tracking set-ups in each case. For tube-bound rats, using a single appropriately placed binocular tracker, uninterrupted tracking was possible greater than 95 per cent of the time. For freely moving rats, simulations and measurements of a live subject indicated that two opposed binocular trackers are sufficient (less than 10% interruption to tracking) for a wide variety of behaviour types. We conclude that reliable tracking of head pose can be achieved with marker-based optical-motion-tracking systems for both tube-bound and freely moving rats undergoing PET studies without sedation. 相似文献
5.
D. Burdette D. Albani E. Chesi N.H. Clinthorne E. Cochran K. Honscheid S.S. Huh H. Kagan M. Knopp C. Lacasta M. Mikuz P. Schmalbrock A. Studen P. Weilhammer 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2009,609(2-3):263-271
Very high resolution images can be achieved in small animal PET systems utilizing solid state silicon pad detectors. As these systems approach sub-millimeter resolutions, the range of the positron is becoming the dominant contribution to image blur. The size of the positron range effect depends on the initial positron energy and hence the radioactive tracer used. For higher energy positron emitters, such as and , which are gaining importance in small animal studies, the width of the annihilation point distribution dominates the spatial resolution. This positron range effect can be reduced by embedding the field of view of the PET scanner in a strong magnetic field. In order to confirm this effect experimentally, we developed a high resolution PET instrument based on silicon pad detectors that can operate in a 7 T magnetic field. In this paper, we describe the instrument and present initial results of a study of the effects of magnetic fields up to 7 T on PET image resolution for and point sources. 相似文献
6.
Eun Ji Han Sang‐Hoon Lee Hyung Sun Sohn Yong‐An Chung Soo Kyo Chung 《International journal of imaging systems and technology》2012,22(4):245-249
The testis shows physiologic uptake in flourine‐18 fluorodeoxyglucose (F‐18 FDG) positron emission tomography (PET). The purpose of this study was to examine the degree of FDG uptake of normal testis on PET/computed tomography (CT), especially in relationship to various clinical parameters. We obtained the maximum standardized uptake value (SUVmax) and the mean standardized uptake value (SUVmean) of each testis from PET/CT of 166 healthy men. We also calculated the testis‐to‐muscle (T/M) ratio, defined as the SUVmean of the testis divided by the SUVmean of the right thigh muscle. Subjects completed a questionnaire on their medical history and sexual habits, including frequency of sexual intercourse, latest date of sexual intercourse, and vasectomy history. We then evaluated the association between imaging parameters and sexual habits. The mean age of subjects was 48 ± 10 years (range, 21–74), and the mean volume of each testis was 17.1 ± 4.5 cm3 (range, 7.4–32.4). The mean SUVmax was 3.6 ± 0.5 (range, 2.2–5.5), the mean SUVmean was 2.5 ± 0.4 (range, 1.6–3.8), and the mean T/M ratio was 4.2 ± 0.8 (range, 2.3–7.3). Of the 166 subjects, 51 reported having sexual intercourse zero times per month and 109 had sexual intercourse at least per month. The interval between the latest date of sexual intercourse and PET/CT was less than 3 days in 48 subjects; between 3 days and 1 month in 58; and greater than 1 month in 60. Twenty subjects were currently vasectomized. The T/M ratio was significantly correlated with age (P = 0.040) but not with sexual habits. On the PET/CT, normal testicular FDG uptake decreased as age increased. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 245–249, 2012 相似文献
7.
An approach is suggested for determining the reliability of incidentally corrected terrestrial navigation system information
without presuming finding in explicit form the empirical distribution density of navigation parameter errors.
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Translated from Izmeritel’naya Tekhnika, No. 5, pp. 35–39, May, 2007. 相似文献
8.
J.ízek 《材料科学技术学报》2018,34(4):577-598
Positron is an excellent probe of lattice defects in solids. A thermallized positron delocalized in lattice can be trapped at open volume defects, e.g. vacancies, dislocations, grain boundaries etc. Positron annihilation spectroscopy is a non-destructive technique which enables characterization of open volume lattice defects in solids on the atomic scale. Positron lifetime and Doppler broadening of annihilation photo-peak are the most common observables related to positron annihilation process. Positron lifetime spectroscopy enables to identify defects in solids and to determine their concentrations while coincidence measurement of Doppler broadening provides information about local chemical environment of defects. This article provides a review of the state-of-art of defect characterization in bulk metallic materials by positron annihilation spectroscopy. Advanced analysis of positron annihilation data and recent developments of positron annihilation methodology are described and discussed on examples of defect studies of metallic materials. Future development in the field is proposed as well. 相似文献
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Z. Papp I. Uray 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2002,480(2-3):788-796
A new grab sampling method has been developed for the measurement of 18F attached to aerosol particles. It is based on direct β-counting of filtered aerosol sample over successive time intervals by an end-window Geiger–Müller counter. The effect of the progeny of radon and thoron on the β-counting rate is separated by analysing the decay curve. The defined solid angle absolute counting was used to evaluate the efficiencies for 18F and for the progeny of radon and thoron one by one. Absolute activity concentration of 18F can be determined with less than 10% systematic error. Glass-fibre filter and high sampling flow rate are applied, leading to a detection limit for 18F of less than 1 Bq m−3. The method was tested under different circumstances in the PET centre of University of Debrecen, Hungary. 相似文献
11.
Feng Zhu Xiaoyang Lin Peng Liu Kaili Jiang Yang Wei Yang Wu Jiaping Wang Shoushan Fan 《Nano Research》2014,7(4):1-8
The work function (WF) of graphene is an essential parameter in graphene electronics. We have derived the WF of graphene by the thermionic emission method. Chemical vapor deposition (CVD)-grown single-layered polycrystalline graphene on copper foil is transferred to a cross-stacked carbon nanotube (CNT) film drawn from a super-aligned multiwalled CNT array. By decreasing the pore size of the CNT film, the as-prepared CNT-graphene film (CGF) can be Joule heated to a temperature as high as 1,800 K in vacuum without obvious destruction in the graphene structure. By studying the thermionic emission, we derive the WF of graphene, ranging from 4.7 to 4.8 eV with the average value being 4.74 eV. Because the substrate influence can be minimized by virtue of the porous nature of the CNT film and the influence of adsorbents can be excluded due to the high temperature during the thermionic emission, the measured WF of graphene can be regarded as intrinsic. 相似文献
12.
The temperature dependence of secondary ion emission was investigated for Fe-Ni ferromagnetic alloys with different Curie points Tc and elemental composition: 35% Ni 65% Fe (Tc=240°C), 40% Ni 60% Fe (Tc=360°C), and 50% Ni 50% Fe (Tc=530°C). The alloy 79% Ni 16% Fe 5% Mo (Tc=345°C) was also studied. The spatial distribution of Ni+ and Fe+ secondary ions emitted from the (1 1 1) face of invar and permalloy single crystals was shown to be anisotropic with pronounced ion-yield maximum for both components in the 〈1 1 0〉 directions. The shape of the energy distribution of Ni+ and Fe+ ions was found to be virtually identical for all the alloys under investigation with a most probable energy at 7 eV and a width at half-maximum of 12 eV. The temperature dependence of the Ni+ and Fe+ emission has a maximum near the Curie point of the investigated alloys and another maximum at the Curie point of nickel which may indicate the precipitation of nickel into microscopic islands on the surface as a result of heating and sputtering. Auger analysis of the surface composition in the surface layers showed a variation in concentration of oxygen and carbon atoms when Fe-Ni alloys pass from the ferromagnetic to the paramagnetic state and this must affect also the secondary ion emission of alloy components. 相似文献
13.
A. Callejo J. García de Jalón 《International journal for numerical methods in engineering》2014,100(12):933-952
The usefulness of sensitivity analyses in mechanical engineering is very well‐known. Interesting examples of sensitivity analysis applications include the computation of gradients in gradient‐based optimization methods and the determination of the parameter relevance on a specific response or objective. In the field of multibody dynamics, analytical sensitivity methods tend to be very complex, and thus, numerical differentiation is often used instead, which degrades numerical accuracy. In this work, a simple and original method based on state‐space motion differential equations is presented. The number of second‐order motion differential equations equals the number of DOFs, that is, there is one differential equation per independent acceleration. The dynamic equations are then differentiated with respect to the parameters by using automatic differentiation and without manual intervention from the user. By adding the sensitivity equations to the dynamic equations, the forward dynamics and the independent sensitivities can be robustly computed using standard integrators. Efficiency and accuracy are assessed by analyzing three numerical examples (a double pendulum, a four‐bar linkage, and an 18‐DOF coach) and by comparing the results with those of the numerical differentiation approach. The results show that the integration of independent sensitivities using automatic differentiation is stable and accurate to machine precision. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
14.
V. A. Strizhalo Yu. V. Dobrovolskii M. P. Zemtsov V. P. Maslov Yu. M. Rodichev V. E. Bodunov 《Strength of Materials》2007,39(1):64-67
The optical systems operating under great ambient temperature drops use materials with special properties, e.g., with invariable
geometric characteristics, such as Zerodur glass ceramic with zero coefficient of thermal expansion. Strong precision joints
of parts are necessary elements of systems. Fracture processes in loaded materials are studied by the method of acoustic emission,
which allows one to record the instant of crack initiation and to study crack development in a brittle material during loading.
The evaluation of the strength of brittle optical materials and their nanojoints by the method of acoustic emission has been
shown to have good prospects. It has been found that the number of acoustic emission pulses depends on specimen strength.
In tests of nanojoints of pyroceramics, two characteristic fracture modes are possible: with crack propagation into the specimen
material and without crack propagation beyond the seam limits. The method of acoustic emission assures reliable recording
of these fracture modes.
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Translated from Problemy Prochnosti, No. 1, pp. 94–99, January–February, 2007. 相似文献
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Jorge Núez Xavier Otazu María Teresa Merino 《International journal of imaging systems and technology》2005,15(5):225-235
Spatial resolution is a key parameter of all kind of images. This is of particular importance in fields as, for example, medicine or remote sensing. The nominal resolution of a positron emission tomography (PET) or nuclear magnetic resonance (NMR) scanners are directly related to the size, number, and position of the detectors in the scanner ring. Also, the nominal spatial resolution of the remote sensing satellites is a well‐known characteristic because it is directly related to the area in ground that represents a pixel in the detector. Nevertheless, in practice, the actual resolution of a medical scanner image or of an image obtained from a satellite is difficult to know precisely because it depends of many other factors. However, if we have two or more images of the same region of interest, obtained using similar or different instruments, it is possible to compare the relative resolution between them. In this paper we propose a wavelet‐decomposition‐based method for the determination of the relative resolution between two images of the same area. The method can be applied, in principle, to any kind of images. As example, we applied the method to pairs of remote sensing and medical images. In the case of remote sensing, we computed the relative resolution between SPOT‐3, LANDSAT‐5 and LANDSAT‐7 panchromatic and multispectral images taken under similar as well as under very different conditions. In the case of medical imaging, we computed the relative resolution between a pair of simultaneously obtained PET and NMR images of the same object. On the other hand, if we know the true absolute resolution of one of the images of the pair, we can compute the resolution of the other. Thus, in the last part of this paper, we describe a spatial calibrator that we have designed and constructed to help compute the absolute resolution of a single remotely sensed image, presenting an example of its use. © 2006 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15, 225–235, 2005 相似文献
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碳纳米管(CNT)具有良好的场发射特性,研究表明,垂直于基板的碳纳米管具有较其他取向更大的场发射能力,本文介绍一种在大面积基板上使碳纳米管取向垂直的方法,通过有关参数的实验测试,研究了解场发射能力提高程度,并估算场增强因子。本方法对制备大屏幕场发射显示器(FED)具有积极意义。 相似文献