计算机X射线影像（CR）图像质量原理和测试方法

针对计算机X射线影像（CR）扫描仪研发过程中对图像质量评价的需要,对CR图像质量原理进行了研究和归纳,并总结了一套测试方法。测试方法涵盖了CR图像质量中最常用的几个指标：空间分辨率、对比度分辨率、空间精度、图像噪声、CNR、量子探测效率（DQE）、MTF、伪影和擦除率等。根据这套测试方法对某CR原型机进行了验证,满足了设计和制作过程中对图像质量评价的需要。     

闪烁光纤阵列用于高能射线成像的可行性研究

本文通过对塑料闪烁光纤阵列在高能X或γ射线下的特性研究,分析了利用闪烁光纤阵列作为高能成像探测器的可能性。采用了基于蒙特卡罗的模拟方法,分析了闪烁光纤在高能射线下所成图像的质量,并且模拟计算了表征图像质量的信噪比(SNR),探测量子效率(DQE)以及调制传递函数(MTF)。通过这些计算得到闪烁光纤阵列有着传统闪烁屏所不具有的一些特性,把闪烁光纤的这些特点应用于高能成像中是完全可行的。     

A high-sensitivity CCD system for parallel electron energy-loss spectroscopy (CCD for EELS)

A cooled frame transfer CCD camera system was developed and tested as a parallel detector in an electron energy-loss spectrometer mounted on a transmission electron microscope. The use of a shutterless camera with a frame transfer CCD collected virtually 100% of the photon signal with a reasonably fast acquisition time. The system detective quantum efficiency was over 90% under normal experimental conditions. Because of the low channel to channel gain variations in the CCD, the signal-to-noise ratio and the detection limit were substantially better than that obtained with a silicon intensified target (SIT) camera, and direct fitting to the standard data was feasible. Quantitation at the phosphorus L edge generated from a phosphoprotein, Phosvitin, showed that, under identical experimental conditions, direct fitting of spectra obtained with this CCD system gave better sensitivity than that given by the SIT camera system. Because of its larger pixel charge well, the CCD system can also operate at a much higher beam current, resulting in a significant reduction in the time required for elemental mapping at a given sensitivity.     

Characterization of a direct detection device imaging camera for transmission electron microscopy

The complete characterization of a novel direct detection device (DDD) camera for transmission electron microscopy is reported, for the first time at primary electron energies of 120 and 200 keV. Unlike a standard charge coupled device (CCD) camera, this device does not require a scintillator. The DDD transfers signal up to 65 lines/mm providing the basis for a high-performance platform for a new generation of wide field-of-view high-resolution cameras. An image of a thin section of virus particles is presented to illustrate the substantially improved performance of this sensor over current indirectly coupled CCD cameras.     

Enhanced imaging in low dose electron microscopy using electron counting

We compare the direct electron imaging performance at 120 keV of a monolithic active pixel sensor (MAPS) operated in a conventional integrating mode with the performance obtained when operated in a single event counting mode. For the combination of sensor and incident electron energy used here, we propose a heuristic approach with which to process the single event images in which each event is renormalised to have an integrated weight of unity. Using this approach we find enhancements in the Nyquist frequency modulation transfer function (MTF) and detective quantum efficiency (DQE) over the corresponding integrating mode values by factors of 8 and 3, respectively.     

Detective quantum efficiency of electron area detectors in electron microscopy

Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology. We present MTF and DQE measurements for four types of detector: Kodak SO-163 film, TVIPS 224 charge coupled device (CCD) detector, the Medipix2 hybrid pixel detector, and an experimental direct electron monolithic active pixel sensor (MAPS) detector. Film and CCD performance was measured at 120 and 300 keV, while results are presented for the Medipix2 at 120 keV and for the MAPS detector at 300 keV. In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated. We also show that part of the response of the emulsion in film comes from light generated in the plastic support. Computer simulations of film and the MAPS detector have been carried out and show good agreement with experiment. The agreement enables us to conclude that the DQE of a backthinned direct electron MAPS detector is likely to be equal to, or better than, that of film at 300 keV.     

Detective quantum efficiency of a phosphor-coupled photodiode array detector for use in digital X-ray tomosynthesis systems

The X-ray imaging performance of a phosphor-coupled photodiode array detector was assessed for use in a cone-beam computed tomography (CBCT) system for printed-circuit board inspection. The radiographic image quality of a detector is mainly responsible for the tomographic image quality. The radiographic image quality can be improved by increasing the X-ray exposure level, but CT scans at higher exposure can impose an enormous heat load on the X-ray tube. In this study, the detective quantum efficiency (DQE) was used to describe the image quality per air kerma as a metric to assess the detector performance. Measurement results were obtained for 40-kVp and 50-kVp tungsten-target X-ray beams, which show that the DQE of the detector is tolerant of air kerma levels as low as 0.8 μGy. Below this level, the electronic noise of the detector system could degrade the DQE performance. The concept of DQE and the measurement procedure are described, including the modulation-transfer function and the noise-power spectrum.     

原位电子显微学数码相机的研发

本文首先简单回顾了原位电子显微学的发展历史。电子显微镜的不断更新换代和其他新配件的出现对原位电子显微学的发展起了很大的作用。其中记录和采集图像使用的相机尤为重要。本文重点讨论了原位电子显微学数码相机设计的主要参数（运行速度,分辨率,和灵敏度）.并给出两例使用新一代数码相机的原位电子显微学应用实例。最后展望未来原位电子显微学的发展方向和新的需求。