医用诊断X射线半价层的测量

介绍了医用诊断X射线半价层测量的原理与曲线拟合法、平均值法、内插法、作图法等四种测量方法,结合实验数据分析了平均值法、内插法和拟合法的特点。医用诊断X射线束通常为“宽束”,曲线拟合法测量半价层需考虑积累因子的影响,通过调整吸收片厚度能快速计算出半价层;平均值法对于宽束X射线在较大的吸收片厚度范围内多次测量不能减小误差;内插法测量时内插间距的选择直接影响测量结果;采用平均值法和内插法时,所选吸收片厚度应使K/K0分布在1/2两侧。     

Dose estimation by EPR spectroscopy of tooth enamel in Chinese medical diagnostic X-ray workers

Individual accumulated doses were determined by electron paramagnetic resonance spectroscopy of tooth enamel in Chinese medical diagnostic X-ray workers. Dose determination was performed using a specially developed automatic spectrum processing procedure. The determined dose values owing to X rays for the three workers with entry year (the year they began their career as medical diagnostic X-ray workers) in the 1950s ranged from 435 to 903 mGy, the converted effective doses ranged from 91 to 190 mSv.     

建立医学诊断X射线参考辐射场技术研究

为解决国家和地区使用的X射线诊断辐射剂量仪及其相关X射线探测仪辐射计量的检定和校准问题,必须在全国范围内构建医学诊断X射线标准辐射场,提供标准辐射剂量值。按照IEC 61267医用诊断X射线设备辐射特性使用的条件标准,分析辐射质和标准辐射条件,介绍RQR、RQA、RQC、RQT、RQN、RQB、RQR-M、RQA-M、RQN-M、RQB-M的具体技术要求和建立方法 ,为国内计量部门、专业实验室、X射线设备生产企业提供建设方案和技术支持。     

Count rate and dynamic range of an X-ray imaging system with MCP detector

X-ray imaging system with edge-on MCP detector has recently been evaluated for potential application in medical imaging. Although this system has been able to provide good quality images, its clinical implementation is limited by its low count rate. The system count rate was limited by a delay line position encoding electronics, which processes the events serially. The count rate of the MCP was also limited because of high gain required for delay line electronics. In this work, the count rate and dynamic range of the system was evaluated. The count rate limitation due to readout electronics and MCP was measured separately. Pulse counting and charge integrating modes of the MCP detector was used. Photon beams for these measurements were generated using an X-ray tube at 50 and 90 kVp peak potentials with 41 and 75 keV average photon energies, respectively. The electronics dead time was measured to be 20% at 200 kHz total system count rate. In addition, 15–30% of the photon signals were not detected by delay line electronics due to exponential pulse height distribution of the MCP signals. The exponential pulse height distribution of the MCP was due to the edge on illumination mode of the MCP and the high energy X-ray photon beam. Image artifacts due to dead time and signal loss were evaluated. Multichannel ASIC readout electronics was considered as a potential solution to the count rate and dynamic range problem. It was shown that the edge-on MCP detector can operate in pulse counting mode at low gains of 10⁴–10⁵ e/photon required for ASIC electronics. It was also shown that at this low gain, the MCP count rate can be increased up to 1.33×10⁶ count/s/pixel, for 100 μm detector pixels, which is appropriate for clinical X-ray imaging.     

(HP)Ge Measurement of spectra for diagnostic X-ray beams

The X-ray spectra applied in diagnostic radiology to the energy range between 50 and 125 kVp, were experimentally determined using a high-purity germanium detector, (HP)Ge, coupled to a multichannel analyser. A simple stripping procedure was implemented, according to that described by Seelentag and Panzer, to correct the pulse height distribution and then to determine the photon spectra. The measurements were performed for those conditions where the X-ray beam is transmitted through Pb filters 0.2-0.7 mm thick. It was necessary to estimate the effective dose in the same way that it is done for radiology diagnosis room shielding projects. The spectra were also determined to the X-ray qualities recommended by the IEC for primary diagnostic X-ray and for X-ray beams attenuated by aluminium filters 2.5-42.5 mm thick. The spectra obtained were compared with data derived from the literature presenting good agreement.     

医用诊断X射线非介入电流仪校准技术研究

为保障我国目前使用的X射线诊断光机曝光电流量值的准确性,开展医用诊断X射线非介入电流测量仪计量校准的研究,分析国内电流仪的校准方法和诊断辐射源检定规程,结合非介入电流仪测量的物理环境条件,提出非介入电流仪的计量指标要求、校准测试设备的技术要求。详细介绍开展校准工作的测试原理和数据处理方法,将诊断辐射源首次引入到电流仪的校准工作中作为触发信号,利用标准电流源,采用多台非介入电流测量仪进行实验研究和分析,证明校准工作的科学性、可操作性、有效性。     

X-ray spectral determination by successive modifications of the beam intensity

A simple and practical indirect method to determine spectra from X-ray tubes has been developed on the basis of successive modifications of beam flux. The beam is either scattered at different angles or attenuated by metal foils and the intensity is measured by an ionization chamber. The data are analyzed by means of an iterative program that solves a system of equations whose unknowns define a parametric fit of the X-ray spectrum. We have checked this method with simulated measurements of tabulated spectra, as well as with our own measurements on available X-ray apparatus and for several different applied voltages.     

Evaluation of the GSO:Ce scintillator in the X-ray energy range from 40 to 140 kV for possible applications in medical X-ray imaging

The purpose of the present study was to evaluate, under X-ray medical imaging conditions, the X-ray luminescence efficiency (XLE) and the optical quantum gain (OQG) of the Gd₂SiO₅:Ce scintillator in single crystal form, suitable for tomographic applications. Intrinsic physical properties and light emission characteristics of the Gd₂SiO₅:Ce scintillator, were also studied. Both experimental and Monte Carlo techniques were used. Various X-ray tube voltages (40–140 kV), currently employed in X-ray imaging applications, were used. XLE was found to vary slowly with X-ray tube voltage from (0.021±0.003) to (0.017±0.003). OQG varied from (317±18) to (466±23) light photons per incident X-ray. These values were adequately high for imaging applications using the particular energy range. Additionally, it was found by Monte Carlo simulations that for crystal thicknesses higher than 0.5 cm both XLE and OQG reached saturation levels, indicating that higher thickness crystals are of no practical use in X-ray medical imaging.     

Short range ordering in amorphous In-Se films by wide-angle X-ray scattering

Wide-angle X-ray scattering studies were performed on In-Se amorphous films, obtained by thermal evaporation, with selenium content of 60 and 66 at.%. The intensities were recorded in the scattering vector range between 3 and 160 nm^–1. Structural information about the local structure of the amorphous In-Se films has been derived from the radial distribution function using the curve-fitting method. The experimental results have been compared with model based simulations. The obtained structural parameters indicate that for In₄₀Se₆₀ In-In, In-Se and Se-Se contributions are involved in the near-neighbour coordination sphere. As the Se content is increased, the number of In-In bonds is reduced to zero, within the precision of the method. For both amorphous films In is tetrahedrally coordinated while Se has three near neighbours on the average.     

Circularly polarization line filters in the soft X-ray range

A feasibility study of the application of the recently discovered strong magnetic X-ray dichroism of rare earth materials to the production of circularly polarized X-rays is reported. A device is described that can be inserted downstream from a high resolution double beryl crystal monochromator. Calculations show that 45% transmission can be obtained with filters that yield 99% circular polarization in the energy range 950–1500 eV. Advantages of the proposed device are the low costs, the ease of installation and the high product of transmission × polarization.     

Improving the performance of the MWPC X-ray imaging detector by means of the multi-step avalanche technique

X-ray imaging systems based on conventional MWPC technology and artificial delay line readout techniques have been developed at RAL for several applications over a period of some eight years. Successful as this effort has been, it is now perceived that very limited scope exists for the further improvement of the imaging capability of the standard MWPC design. Attention has therefore been turned to the possibility of exploiting the multi-step avalanche (MSA) system of electron multiplication in this context. Results from a prototype system are presented which show spatial resolution better than that achieved in our MWPC systems with no wire artefacts in the image. The facility for controlling the effective depth of the detector electronically is also demonstrated so offering some alleviation of the parallax problem common to all gaseous X-ray detectors.     

Superconducting single-photon detector for the visible and infrared spectral range

Abstract

We present results on dark count rates and spectral sensitivities of superconducting single-photon detectors in the visible and near-infrared spectral range. The active detector element is a nanometre-sized (a few nanometres thick and less than 100nm wide) meander line carrying a supercurrent. The superconducting materials are NbN and Nb, respectively. The NbN detector exhibited a flat spectral sensitivity up to about 2.4μm. Fluctuations of the superconducting order parameter are considered as a major source of dark count events. A simple model and its limitations to explain the observed dark count rates is discussed.     

High dynamic range bio-molecular ion microscopy with the Timepix detector

Highly parallel, active pixel detectors enable novel detection capabilities for large biomolecules in time-of-flight (TOF) based mass spectrometry imaging (MSI). In this work, a 512 × 512 pixel, bare Timepix assembly combined with chevron microchannel plates (MCP) captures time-resolved images of several m/z species in a single measurement. Mass-resolved ion images from Timepix measurements of peptide and protein standards demonstrate the capability to return both mass-spectral and localization information of biologically relevant analytes from matrix-assisted laser desorption ionization (MALDI) on a commercial ion microscope. The use of a MCP-Timepix assembly delivers an increased dynamic range of several orders of magnitude. The Timepix returns defined mass spectra already at subsaturation MCP gains, which prolongs the MCP lifetime and allows the gain to be optimized for image quality. The Timepix peak resolution is only limited by the resolution of the in-pixel measurement clock. Oligomers of the protein ubiquitin were measured up to 78 kDa.     

用HXCF测量物质X射线质量衰减系数

X射线质量衰减系数是研究X射线的一个重要物理量,硬X射线探测器地面标定装置由于其单色性、稳定性以及其可测的绝对光子数,成为了研究质量衰减系数的一套理想装置.使用Cu、A12种不同材料分别在X射线能量为30 keV、50 keV、80 keV、100 keV和110 keV的情况下对其质量衰减系数进行测量,并将测量值与NIST的参考值进行了对比,得到了其标准偏差.根据NIST提供的质量衰减系数曲线,验证了Cu和Al在110keV处的质量衰减系数,为进一步研究做好了基础.     

Measurement of X-ray tube accelerating potential by differentialbeam filtration

Indirect determination of X-ray generator kilovoltage (kV) using the ratio of differentially filtered beam measurements has been known for 20 years. Measurement of generator potentials used for diagnostic computed tomography (CT), conventional X-ray, and mammography typically requires filter cassettes or special instruments in the X-ray beam; the resulting readings are usually accurate within ±2%. A related technique, free of many theoretical and practical restrictions, provides simplified generator potential measurements with significantly improved accuracy. Curve fitting provides a simple relationship predicting generator kV from a measured filter response ratio. Routine use has established that this technique is robust, reliable, repeatable, and more accurate than most working standards