A survey on performance status of mammography machines: image quality and dosimetry studies using a standard mammography imaging phantom

It is essential to perform quality control (QC) tests on mammography equipment in order to produce an appropriate image quality at a lower radiation dose to patients. Imaging and dosimetric measurements on 15 mammography machines located at the busiest radiology centres of Mumbai, India were carried out using a standard CIRS breast imaging phantom in order to see the level of image quality and breast doses. The QC tests include evaluations of image quality and the mean glandular doses (MGD), which is derived from the breast entrance exposure, half-value layer (HVL), compressed breast thickness (CBT) and breast tissue compositions. At the majority of the centres, film-processing and darkroom conditions were not found to be maintained, which is required to meet the technical development specifications for the mammography film in use as recommended by the American College of Radiology (ACR). In most of the surveyed centres, the viewbox luminance and room illuminance conditions were not found to be in line with the mammography requirements recommended by the ACR. The measured HVL values of the machines were in the range of 0.27-0.39 mm aluminium (Al) with a mean value of 0.33±0.04 mm Al at 28 kV(p) following the recommendation provided by ACR. The measured MGDs were in the range of 0.14-3.80 mGy with a mean value of 1.34 mGy. The measured MGDs vary between centre to centre by a factor of 27.14. Referring to patient doses and image quality, it was observed that only one mammography centre has exceeded the recommended MGD, i.e. 3.0 mGy per view with the value of 3.80 mGy and at eight mammography centres the measured central background density (CBD) values for mammography phantom image are found to be less than the recommended CBD limit value of 1.2-2.0 optical density.     

Photon counting at telecom wavelengths with commercial InGaAs/InP avalanche photodiodes: Current performance

Abstract

InGaAs/InP avalanche photodiodes operated in the so-called Geiger mode currently represent the best solution to detect single-photon beyond 900nm. They cover the 1100–1650nm wavelength interval, which includes in particular the two windows used for optical communications (1310 and 1550nm). A detection efficiency at 1550nm of 10% with a dark count probability of 10^?5 ns^?1 is common, although significant variations can be encountered. At this efficiency, a FWHM temporal response of 300 ps can be achieved. Afterpulses caused by charges trapped by defects in the high field region of the junction constitute the main performance impairment phenomenon. They enhance the dark count probability and reduce out-of-gate detector blindness. These photon counting detectors can be used in optical time-domain reflectometry to improve the spatial resolution and reduce dead-zone effects. Quantum key distribution over metropolitan area networks also constitutes an important application.     

EURADOS trial performance test for photon dosimetry

Within the framework of the EURADOS Action entitled Harmonisation and Dosimetric Quality Assurance in Individual Monitoring for External Radiation, trial performance tests for whole-body and extremity personal dosemeters were carried out. Photon, beta and neutron dosemeters were considered. This paper summarises the results of the whole-body photon dosemeter test. Twenty-six dosimetry services from all EU Member States and Switzerland participated. Twelve different radiation fields were used to simulate various workplace irradiation fields. Dose values from 0.4 mSv to 80 mSv were chosen. From 312 single results, 26 fell outside the limits of the trumpet curve and 32 were outside the range 1/1.5 to 1.5. Most outliers resulted from high energy R-F irradiations without electronic equilibrium. These fields are not routinely encountered by many of the participating dosimetry services. If the results for this field are excluded, most participating services satisfied the evaluation criteria.     

EURADOS trial performance test for neutron personal dosimetry

This paper reports on the results of a neutron trial performance test sponsored by the European Commission and organised by EURADOS. As anticipated, neutron dosimetry results were very dependent on the dosemeter type and the dose calculation algorithm. Fast neutron fields were generally well measured, but particular problems were noted in the determination of intermediate energy fields and large incident angles, demonstrating the difficulties of neutron personal dosimetry. Of particular concern from a radiological protection point of view was the large number of results underestimating personal dose equivalent. A considerable over-response was noted in a few cases.     

The CERN-EU high-energy reference field (CERF) facility for dosimetry at commercial flight altitudes and in space

A reference facility for the calibration and intercomparison of active and passive detectors in broad neutron fields has been available at CERN since 1992. A positively charged hadron beam (a mixture of protons and pions) with momentum of 120 GeV/c hits a copper target, 50 cm thick and 7 cm in diameter. The secondary particles produced in the interaction traverse a shield, at 90 degrees with respect to the direction of the incoming beam. made of either 80 to 160 cm of concrete or 40 cm of iron. Behind the iron shield, the resulting neutron spectrum has a maximum at about 1 MeV, with an additional high-energy component. Behind the 80 cm concrete shield, the neutron spectrum has a second pronounced maximum at about 70 MeV and resembles the high-energy component of the radiation field created by cosmic rays at commercial flight altitudes. This paper describes the facility, reports on the latest neutron spectral measurements, gives an overview of the most important experiments performed by the various collaborating institutions over recent years and briefly addresses the possible application of the facility to measurements related to the space programme.     

History of personal dosimetry performance testing in the United States

The basis for personal dosimetry performance testing in the United States is ANSI/HPS N13.11 (2001). Now in its third edition, this standard has been in place since 1983. Testing under this standard is administered by the National Voluntary Accreditation Program (NVLAP), and accreditation of dosimetry processors under this program is required by US Nuclear Regulatory Commission (NRC) regulations. The US Department of Energy (DOE) also maintains a testing program for its laboratories and contractors, administered by the Department of Energy Laboratory Accreditation Program (DOELAP). A focus in recent years has been the modification of ANSI/HPS N13.11 to allow acceptance by both testing programs in order to bring harmonisation to US personal dosemeter processing testing. Since there is no type testing program in the US for personal dosemeters, the testing philosophy of ANSI N13.11 has always combined elements of type testing and routine performance testing. This philosophy is explored in detail in this presentation, along with trends in the development of the document to its present state. In addition, a look will be taken at what the future holds for the next revision of the document, scheduled to begin in 2005.     

InGaAsp-i-n photodiodes for fibre-optic communication

High purity layers of In_{1 −x} Ga _x As have been grown by liquid phase epitaxy using a novel impurity gettering technique with rare earth atoms. The electron concentration could thus be decreased from 3 × 10¹⁸ cm⁻³ to 2·4 × 10¹⁵ cm⁻³ and the mobility increased from 7 110 cm²/Vs to 18,981 cm²/Vs (100 K). The excellent quality of the layers has been evidenced by X-ray diffraction and photoluminescence measurements. The fabrication ofp-i-n photodiodes using this technique is described and reliability aspects addressed.     

A Monte Carlo study of the energy dependence of Al2O3:C crystals for real-time in vivo dosimetry in mammography

In a previous experimental study, a novel method for in vivo dosimetry has been investigated, based on radioluminescence (RL) and optically stimulated luminescence (OSL). However, because of the large difference in atomic composition between the detector material and the breast tissue, relatively large energy dependence in low-energy X-ray beams can be expected. In the present work, the energy dependence of Al2O3:C crystals was modelled with the Monte Carlo code EGSnrc using three types of X-ray spectra. The results obtained (5.6-7.3%) agree with a previously determined experimental result (9%) within the combined standard uncertainty of the two methods. The influence of the size of the crystal on the energy dependence was investigated together with the effect of varying the thickness of the surrounding light-protective material. The results obtained indicate a minor effect owing to the thickness of the light-protective material, and a somewhat larger effect from reducing the diameter of the crystal. The outcome of this study can be used to improve the future design of the RL/OSL dosimetry system for use in mammography.     

The user interface and performance of commercial mixed integer programming software

Summary Today's mixed integer programming software packages are still not sophisticated enough to be treated as black boxes. Their efficiency can be augmented considerably by a deep knowledge of their functioning and the degrees of freedom they offer to the user. This paper describes at first the choices of the underlying branch and bound method in seven representative MIP-systems and demonstrates their usage, their profitability and their catches at illustrative examples. An account follows of the procedures and administrative facilities of commercial MIP-modules as far as they are submitted to user influence. An outlook is given on future developments, which can further improve the acceptance and the performance of MIP-software. Finally, some effort assessment criteria are proposed, which help judging the amount of work ahead before and at different stages during the solution process.

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Zusammenfassung Heute verfügbare Softwarepakete der gemischt-ganzzahligen Programmierung sind noch nicht fortgeschritten genug, um als Black Boxes behandelt zu werden. Ihre Effizienz kann durch eine gründliche Kenntnis ihrer Funktionsweise und der dem Benutzer angebotenen Freiheitsgrade beträchtlich gesteigert werden. Diese Veröffentlichung beschreibt zuerst die Auswahlmöglichkeiten der zugrundeliegenden Branch und Bound Methode in sieben repräsentativen MIP-Systemen und demonstriert anhand illustrativer Beispiele deren Anwendung, deren Nutzen und deren Fußangeln. Im Anschluß werden Proceduren und administrative Funktionen in kommerziellen MIP-Modulen, soweit sie dem Benutzereinfluß unterliegen, dargestellt. Ein Ausblick auf zukünftige Entwicklungen zeigt, wie sich Akzeptanz und Leistungvon MIP-Software steigern können. Schließlich werden einige Kriterien zur Aufwandsabschätzung vor und in verschiedenen Stadien während des Lösungsprozesses vorgeschlagen.

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List of Symbols c vector of objective function coefficients of continuous variables - C matrix of coefficients of continuous variables - d vector of objective function coefficients of integer variables - D matrix of coefficients of integer variables - d ₁ distance betweenF _as and X ₀ ^* - d ₂ distance betweenF _as andF _bk - d _j ^– estimated functional value degradation when lowering the value ofy _j by one unit - d _j ⁺ estimated functional value degradation when rising the value ofy _j by one unit - E _k estimation of best functional value of any integer solution contained in waiting nodek - F _as aspiration level; nodes with functional value worse thanF _as are postponed - F _ase aspiration level; nodes with estimationE _k worse thanF _ase are postponed - F _bI functional value of best integer solution known so far - F _bk best functional value of all waiting nodes - F _IT0 functional value of integer optimum - F _k functional value of waiting nodek - F ₀ functional value of continuous optimum - M big positiv real number - p maximum percentage deviation ofF _ITO fromF _bI - skj successor nodej - u distance by whichX ₀ ^* is lower thanF _bI - X ₀ ^* cutoff value; nodes with functional value beyondX ₀ ^* are finally discarded - x vector of integer variables - y vector of integer variables - y _j integer variablej - y _j ^(k) value of integer variablej at nodek - w _j associated weight of integer variabley _j in a Special Ordered Set - ¯w average weight of a Special Ordered Set - [ ] greatest integer smaller than or equal to the argument     

The use of TEPC for reference dosimetry.

The radiation fields on board aircraft are quite complex and cover an energy range that is unusual in ordinary radiation protection work. Usually dosemeters measure only one radiation quality and the mixture found on board makes measurements complicated. There is also some doubt when it comes to the best choice of quantity for this application and no radiation standards exist for this kind of radiation field. For those reasons there is a need to find a standard measurement procedure that could serve as a reference for other, maybe simpler, measurements or for calculations of route doses. The only direct reading dosemeter that both measures the absorbed dose to tissue and the radiation quality (in terms of lineal energy) is the tissue-equivalent proportional counter (TEPC). The instrument was originally developed for scientific purposes and is still used as such. The detector consists of a gas filled cavity surrounded by a few mm thick wall. Both wall and gas consists of tissue-like material. The measurement principles are explained. Results observed with TEPC instruments are demonstrated. A preliminary collection of data reported by different groups from measurements on board aircraft will be shown. The results agree within +/- 20%. The conclusion is that TEPC instruments have the capacity of serving as reference instruments.     

Filter-protected photodiodes for high-throughput enzymatic analysis

This paper relates to the use of a thin film of re-crystallized (polycrystalline) silicon as a low-pass rejection filter in the ultraviolet light range and, more particularly, to the use of this layer as a protective layer for semiconductor diodes. The polycrystalline silicon filters were fabricated by laser annealing a thin film of amorphous silicon deposited by an LPCVD process. A standard component of the polysilicon-gate CMOS process is the boron phosphor silicate glass (BPSG) planarization layer. Since this layer is always applied, the possibility of using it as the isolator between the diode and the filter (and, thereby, omit one SiO/sub 2/ layer) is considered. Using scanning electron microscopy, we compared the crystallization process of the LPCVD silicon film deposited on a glass substrate and on a BPSG layer. The fabrication and the characterization of the filter-protected photodiodes are described in the paper.     

Ultra-thin film photodiodes for use in position sensors

Abstract

A novel optical interferometer based on detecting the standing wave is realized by the newly developed ultra-thin film photodiode. The active layer of the ultra-thin film photodiode is thinner than half the wavelength of the incident light. Only a small part of the incident light is absorbed and the rest passes through the photodiode. This ultra-thin film photodiode can detect the intensity profile of the interference fringe of the standing wave, being inserted in the optical field. Taking advantage of this function, a compact interferometer having no reference arm is realized. The principle, design, fabrication, and performance as the displacement sensor are described. The signal obtained confirms the feasibility of this new interferometer. The displacement direction is also detected by a dual ultra-thin film photodiode with a phase shifter comparing the phases of the two signals.     

商用制冰机的性能研究

主要介绍商用风冷制冰机的工作原理,并通过试验研究影响商用制冰机性能指标的主要因素,验证环境温度和水温变化对制冰机的制冰时间和收冰时间影响较大,制冰时间长短决定制冰机的产冰量、耗电量、耗水量等,其中环境温度对制冰时间影响最大,对制冰机的影响最为显著.     

The many facets of dosimetry

To name a few, we have thermoluminescence dosimetry, electronicdosimetry, even computational dosimetry, but is biodosimetrythe name of the ultimate form of dosimetry? The word would implydetermination of the absorbed dose of ionizing radiation deliveredto a living organism by observing some physical or chemicalchange in the organism induced by the deposition of radiationenergy. Of course, one of the physico-chemical consequencesof exposure to ionizing radiation is the death of cells in anorganism, and     

The preparation of pure niobium for neutron dosimetry purposes

A technique is described for the preparation of high purity niobium for use in fast neutron dosimetry. Based on results of known purification processes for niobium, an optimized method has been developed, consisting of: (1) a double electrolytic refining in an eutectic lithium-, sodium-, potassium-fluoride melt, containing fluoro-potassium niobate (K₂NbF₇), (2) electron beam float zone melting (EBFZM) in ultra high vacuum (UHV) and (3) UHV treatments. Starting with EBFZM of niobium of commercial quality (140 μg/g Ta, 35 μg/g W) the tantalum and tungsten contents were reduced by a first electrolysis to approximately 4 and 4 × 10^?2 μg/g, respectively. For a second electrolytic refining using a salt bath with extremely low tantalum and tungsten contents, this material was subjected to an additional EBFZM process. The niobium metal produced by this step was three times zone melted to reduce those elements (e.g. Fe, Co, Ni, O, N) which increased during the electrolyses. Material produced by this technique has impurity concentrations below 0.4 μg/g of tantalum and 10^?2 μg/g of tungsten. The concentration of the interstitials (C, O, N except H) is below the detection limit of classical analytical methods. A further reduction of the interstitials by annealing treatments in UHV of this material resulted in an electrical residual resistivity ratio (RRR) ρ(295 K)/ρ(4.2 K) = 24 500 indicating an impurity concentration far below 1 μg/g.     

Irradiation stability of silicon photodiodes for extreme-ultraviolet radiation

Photodiodes are used as easy-to-operate detectors in the extreme-ultraviolet spectral range. At the Physikalisch-Technische Bundesanstalt photodiodes are calibrated with an uncertainty of spectral responsivity of 0.3% or less. Stable photodiodes are a prerequisite for the dissemination of these high-accuracy calibrations to customers. Silicon photodiodes with different top layers were exposed to intense extreme-ultraviolet irradiation. Diodes coated with diamondlike carbon or TiSiN proved to be stable within a few percent up to a radiant exposure of 100 kJ/cm2. The changes in responsivity could be explained as being due to carbon contamination and to changes in the internal charge collection efficiency. In ultrahigh vacuum, no indication of oxidation was found.     

The preparation of metal oxide spheres for use in neutron dosimetry

Gelation techniques for the preparation of spherical particles of pure and mixed metal oxide have been developed at Harwell for use in nuclear and non-nuclear applications. Gel precipitation processes have been used to prepare actinide oxide spheres (U, Th, Np and Pu) with chosen diameters in the range 50–1500 μm, principally for use as nuclear fuels. Sol-gel and gel precipitation processes have been developed to prepare oxide spheres (1–2000 μm diameter) of aluminium, silicon, titanium, zirconium and rare earth metals either as pure oxides or often with many other elements added. These materials have a variety of applications e.g. as catalysts and adsorbents.Oxide spheres can be used to advantage in neutron dosimetry because they can be fabricated directly from solutions and the spheres can be handled easily without becoming contaminated with impurities. The size of sphere can be chosen to contain the desired weight of nuclide in the range 5 μ g to 5 mg per sphere for pure oxide spheres. For the lower weights of nuclide required it is preferable to use an inert diluent such as alumina so that the sphere size can be kept large enough for easy handling. Here the nuclide of interest to diluent metal ratio is fixed at the solution stage and consequently each sphere produced contains an oxide mixture of the same composition. As an example of this technique indium-aluminium oxide spheres have been prepared.     

The influence of daily sleep patterns of commercial truck drivers on driving performance

Fatigued and drowsy driving has been found to be a major cause of truck crashes. Lack of sleep is the number one cause of fatigue and drowsiness. However, there are limited data on the sleep patterns (sleep duration, sleep percentage in the duration of non-work period, and the time when sleep occurred) of truck drivers in non-work periods and the impact on driving performance. This paper examined sleep patterns of 96 commercial truck drivers during non-work periods and evaluated the influence these sleep patterns had on truck driving performance. Data were from the Naturalistic Truck Driving Study. Each driver participated in the study for approximately four weeks. A shift was defined as a non-work period followed by a work period. A total of 1397 shifts were identified. Four distinct sleep patterns were identified based on sleep duration, sleep start/end point in a non-work period, and the percentage of sleep with reference to the duration of non-work period. Driving performance was measured by safety-critical events, which included crashes, near-crashes, crash-relevant conflicts, and unintentional lane deviations. Negative binomial regression was used to evaluate the association between the sleep patterns and driving performance, adjusted for driver demographic information. The results showed that the sleep pattern with the highest safety-critical event rate was associated with shorter sleep, sleep in the early stage of a non-work period, and less sleep between 1 a.m. and 5 a.m. This study also found that male drivers, with fewer years of commercial vehicle driving experience and higher body mass index, were associated with deteriorated driving performance and increased driving risk. The results of this study could inform hours-of-service policy-making and benefit safety management in the trucking industry.     

International intercomparison for criticality dosimetry: the case of biological dosimetry

The Institute of Radiation Protection and Nuclear Safety (IRSN) organized a biological dosimetry international intercomparison with the purpose of comparing (i) dicentrics yield produced in human lymphocytes; (ii) the gamma and neutron dose estimate according to the corresponding laboratory calibration curve. The experimental reactor SILENE was used with different configurations: bare source 4 Gy, lead shield 1 and 2 Gy and a 60Co source 2 Gy. An increasing variation of dicentric yield per cell was observed between participants when there were more damages in the samples. Doses were derived from the observed dicentric rates according to the dose-effect relationship provided by each laboratory. Differences in dicentric rate values are more important than those in the corresponding dose values. The doses obtained by the participants were found to be in agreement with the given physical dose within 20%. The evaluation of the respective gamma and neutron dose was achieved only by four laboratories, with some small variations among them.     

商用车EBS比例继动阀性能测试系统设计

针对传统继动阀检测装置已无法满足新型EBS比例继动阀检测需求的现状,基于计算机控制技术、采用高速数据采集与数据处理技术,设计EBS比例继动阀综合性能测试系统,实现在电子制动/气制动、缓慢制动/快速制动工况下,对阀的迟滞特性、静特性、动特性、密封性等项目进行测试。其中,采用电气比例阀伺服控制方式,可实现0~1.0 MPa的气压控制,控制绝对误差为±0.01 MPa;采用可编程电流源电流伺服控制方式,可实现0~1.4 A电流控制,控制绝对误差为±0.01 A。对测试系统进行不确定度评定,实验各项数据重复性良好。测试结果表明:商用车EBS比例继动阀综合性能测试系统的性能稳定,满足测试要求。