影响CR成像质量的若干因素及控制

<正> 近年来,随着CR成像技术在临床中的应用和普及,实现了由传统模拟图像信息向数字化图像信息的转变,使影像质量有了跨时代的飞跃。CR成像系统的构成包括IP(Imaging Piate成像板)、IP登陆工作站、激光扫描主机和图像后处理工作站。按其     

数字乳腺摄影系统的质量控制检测与评价

目的 对3套数字乳腺摄影系统进行质量控制检测与评价。方法 应用欧洲乳腺癌普查和诊断质量控制导则中推荐的方法,结合国内乳腺摄影评价标准,对3套数字乳腺摄影系统进行X线发生器性能质量控制检测与评价;分别应用直接数字化X线摄影技术(DR)、相位对比乳腺摄影(PCM)和计算机X线摄影技术(CR)系统在4个厚度下(30、40、50及60mm)对乳腺专用对比度细节检测模体(CDMAM3.4)进行AEC曝光成像,计算与评价每一厚度下的平均腺体剂量(AGD)和影像质量因子(IQF)。结果 DR和CR的X线机性能检测符合现有标准;等效PMMA厚度分别为30、40、50、60mm时,DR系统的AGD分别为1.20、1.42、1.75、2.20mGy;PCM系统AGD分别是0.82、1.19、1.33、1.70mGy;CR系统AGD为0.59、0.88、1.47、2.19mGy。在相应的模体厚度下,DR系统的IQF值为21.36、21.57、27.25和30.58;PCM和CR系统的IQF值分别为28.02、29.10、35.90、41.24和39.78、39.30、43.85、48.08。结论 GBZ186-2007标准不适用于PCM系统X线机性能部分性能的评价。本研究的3套系统自动曝光下平均腺体剂量均符合欧洲标准。在国内检测规范欠缺的情况下,可参考国际标准或指南对数字乳腺系统进行常规监测。     

CR摄影系统的质量控制

目的：对影响CR图像的各个环节进行研究，探讨提高图像质量的有效方法。方法：对CR图像产生的各个环节，如：摄影体位和曝光参数、IP板的检测和维护、CR阅读器的检验和维护、工作站的质量控制、激光相机的质量管理等进行全面的质量控制和质量管理。结果：CR图像的质量得到明显提高。结论：全方位的质量控制是提高CR图像质量的关键。     

影响CR系统影像质量的因素及其优缺点分析

CR系统是使用可记录并由激光读出X线影像信息的成像板（IP）作为载体，经X线曝光及信息读出处理，形成数字式屏一片影像、目前CR已在国内外临床上广泛应用。在CR系统成像的过程中，对影像质量影响的因素有很多，它们主要存在于信息的采集、信息的读出和信息的处理与记录三个环节中，尤以IP的特征和阅读器的性能更为重要。本文对影响CR系统影像质量的因素及其优缺点进行分析，旨在为提高CR系统影像质量寻找有效的措施和方法。     

数字X线照片影像质量相关因素初步分析

目的：探讨影响数字X线照片影像质量的相关因素，提高数字X线照片影像质量。方法：通过分析计算机X线摄影(CR)与直接数字X线摄影(DR)所产生的数字X线照片影像质量相关因素：曝光量与自动曝光控制(AEC)的使用；DR、CR主机(扫描仪)及图像读取工作站；影像板(IP)因素；图像后处理工作站功能；激光打印机等。针对数字X线照片成像的各个环节加以控制。结果：获得优质数字X线照片影像必需做到：选择合适的曝光条件并合理使用AEC；掌握DR主机、CR扫描仪及图像读取工作站的性能特点；保证IP质量及定期清洗保养IP；充分了解并利用好图像后处理工作站的功能；正确设置配套激光打印机参数。结论：了解影响数字X线照片影像影像质量的相关因素，充分发挥数字X线照片影像图像的后处理优势，可以明显提高数字X线照片影像图像的质控水平。     

X线管焦点对CR空间分辨率的影响分析

空间分辨率是评价CR影像的重要内容，影响CR图像空间分辨率的因素很多，它既与摄影X线机的X线管焦点、摄影条件等因素有关，也与CR系统IP的特性、激光及采样频率有关。又与工作站图像增强处理算法有关．还与激光相机、显示器等软硬拷贝因素有关。为了确切了解X线管焦点对CR空间分辨率的影响，笔者通过实验进行了定量分析，供同道们参考．     

CT扫描机分辨率的检测与分析

分辨率是ＣＴ扫描机的主要性能指标[1 ,2 ] 。分辨率即鉴别能力[3] ,包括高对比分辨率和低对比分辨率。根据卫生部的《ＣＴ装置应用质量检测与评审规范》 ,只要有一项分辨率指标不合格则该机的应用状态即被评为不合格。从 1996年开始 ,作者连续 4年对河北省内所有医疗单位 (部队系统除外 )的ＣＴ机进行了应用质量检测。现就两个分辨率及其主要影响因素介绍如下。一、检测项目和方法1 检测仪器 :美国Ｖｉｃｔｏｒｅｅｎ公司 6 6 0 1型射线曝光测量仪 ,6 6 0 6型ＣＴ专用电离室 ,76 414型剂量模型 ,76 410 4130型ＣＴ性能检测模体。2 检…     

计算机X射线摄影新旧成像板对照研究

计算机X射线摄影(computed radiography,CR)系统,成像板(imaging plate,IP)是记录影像的媒介,即成像设备的关键部件.随着CR的广泛应用,IP使用状况越来越引起关注,笔者根据IP特点,设定高、中、低3种摄影模式,对新旧IP、体膜(成人颅骨标本)摄影,并通过仪器检测等方法,探讨IP影像质量与入射体表剂量之间的关系.     

一台计算机X线摄影系统的状态检测与评价

近十年来,数字影像设备已逐渐普及。许多大型医院已经拥有以成像板（IP）为影像接收器的计算机X线摄影（CR）系统。目前,仅北京地区的医院中各种型号的CR系统已超过100台。我国目前尚未颁布此类设备的质量控制检测标准。     

PACS图像显示器质量控制的初步研究

目的探讨放射科PACS系统中图像显示器的质量保证(QA)、质量控制(QC)问题。方法参考美国医学物理学会第18工作组(AAPMTG18)制定的测试图和质量评估标准,利用光度计、显示器校正软件,对3种型号的BARCOCRT灰阶显示器进行季度性定量检测。内容包括:DICOM灰阶标准显示函数校正、最高亮度和最低亮度检测、亮度均一性检测、显示器分辨率、几何失真校正。结果显示器的各项性能指标都符合AAPMTG18规范。放射科95%的医学图像依靠PACS显示器做出了诊断。结论PACS图像显示器的质量控制是确保数字化医疗环境优质性的重要措施。     

CT机质量控制检测的探讨

目的:CT机质量控制检测方法的探讨及应用。方法:用美国模体实验室的Catphan 500模体和瑞典奥利科公司的Solidose 400剂量仪检测CT机扫描架的定位光精度、扫描床运动精度、层厚、CT值线性、视野均匀性、噪声、高对比度分辨率、低对比度分辨率和CT剂量指数(CTDI)。结果:所检测CT机作为整机均合格,但部分指标不合格。结论:通过对噪声、CT线性、对比度分辨率等图像性能参数的检测,可有效保证系统性能良好和维持最优化的图像质量;对CTDI的检测,可及时了解辐射危险水平,进而优化扫描方案,在保证诊断的前提下降低病人受照剂量。     

A comparison of low contrast performance for amorphous Silicon/caesium iodide direct radiography with a computed radiography: A contrast detail phantom study

A range of digital image acquisition devices exists in diagnostic radiology. This study compares contrast performance of two such systems: an amorphous Silicon/caesium iodide (a-Si:CsI) based flat panel (DR) digital chest radiography system and a computed radiography (CR) system. Images of a contrast detail resolution phantom were acquired at a range of radiation doses. Three observers assessed all hardcopy images using a four-alternative forced choice observer perception technique. Contrast detail performance was calculated and low contrast performance quantified.The DR system demonstrated significantly better low contrast performance and potential dose savings of up to 75% compared to the CR system. Threshold levels of contrast detail resolution were defined and levels of under- and over-exposure, compared to the threshold level, were highlighted. Both systems were noise limited at lower exposures and latitude limited at higher exposures. The results demonstrate that the DR system should perform better than the CR system under typical clinical conditions relevant to chest radiography particularly for the detection of low contrast details such as lung metastases or pneumothoraces.     

Acceptance testing of Computed Radiography systems

Acceptance testing of computed radiography systems (CR) is required to verify not only image quality but also compliance with the manufacturer's specifications. Therefore, CR acceptance testing is manufacturer-specific. This paper describes a series of performance tests performed on a large number of CRs (FCR 5000, Fuji) recently acquired by our institution. In particular we describe the following tests: dark noise, uniformity, exposure calibration, linearity and autoranging, limiting resolution, noise and low-contrast resolution, spatial accuracy, laser-beam function, erasure thoroughness, aliasing, grid response. Special attention is given to the practical aspects related to measurement and subsequent image analysis. We report the results obtained in the various tests. No significant variations from the reference levels were found. Nonetheless, in some cases the operating procedures had to be adapted.     

曝光条件、IP尺寸等与CR照片影像的空间分辨力

目的：探讨曝光条件、IP尺寸等与CR照片影像空间分辨力的关系。方法：依据Siemens点数法曝光条件表，在点数不变的情况下换算出摄影部位手的数组曝光条件，选用四种不同尺寸的IP及大小焦点，分别对矩形波测试卡进行摄影。采用无放大和放大2倍的后处理技术，视读并记录CR照片影像的空间分辨力数值，分析其影响CR照片影像空间分辨力的条件。结果：①摄影部位、曝光条件相同，CR照片影像的空间分辨力，小焦点大于大焦点；②摄影部位、曝光条件及焦点大小相同，CR照片影像的空间分辨力随IP尺寸的增加而减小；③CR照片影像的空间分辨力，放大2倍的照片影像明显高于无放大处理的照片影像；④适宜的曝光条件可提高CR照片影像的空间分辨力。结论：影响CR照片影像空间分辨力的条件：小尺寸IP大于大尺寸IP；小焦点大于大焦点；适宜的后处理放大倍数大于无放大处理；适宜的曝光条件组合大于其它组合。     

Low contrast detectability of a new CR system with two-sided reading

A new imaging plate (IP) with a transparent support and reading system that can detect emissions from both sides of the IP has been developed and has already been introduced in some facilities. In this study, low contrast threshold detectability was investigated experimentally for a CR system with a two-sided reading system (new CR) and for a conventional CR system. Images of a Contrast-Detail phantom were obtained with the new and conventional CR systems at dose levels corresponding to 26%, 49%, 82%, 103%, and 164% of the dose used for the screen-film system. Using an observer performance study of Contrast-Detail phantom images, the threshold contrast of disk-shaped objects ranging from 0.3 mm to 4.0 mm in diameter was determined. We also calculated image quality figure (IQF) from the results of observation. The new CR system showed significantly better contrast detectability than the conventional CR system. The use of a new CR system provided a reduction of approximately 25% in radiographic dose while providing comparable IQF.     

CT机的性能检测和临床照片评估

目的：探讨ＣＴ 机的性能检测方法。材料和方法：ＣＴ 设备２０ 台。性能检测参数为层厚、ＣＴ 值线性与对比度标度、均匀性、噪声、空间分辨力、密度分辨力、诊视床定位光精度、诊视床运动精度、剂量指数（ ＣＴＤＩ） 等九项。用Ｃａｔｐｈａｎ体模以及ＲＡＤＣＡＬ 剂量测试设备对ＣＴ 机进行性能参数检测。用近２ 个月多部位照片进行临床照片评估。结果：９ 台ＣＴ 机全部参数合格，其中有３ 台照片质量评估为１ 等，６ 台照片质量评估为２ 等，７ 台ＣＴ 机有１ 项参数不合格，照片质量评估为２ 等，４ 台ＣＴ 机有３ 项以上参数不合格，照片质量评估为２ 等。结论：该检测方法可对ＣＴ 机的各项参数作精确的检测，能够满足ＣＴ 机质量保证性能检测的要求。     

Noise properties in the fading of the imaging plate on a computed radiography system

Fading of the imaging plate (IP) in computed radiography (CR) systems with photostimulable phosphors is known well. The relation between noise properties and the fading of the IP in a CR system was investigated. Uniform exposure for the IP with various times between exposure and readout for the same exposure was used for this study. The relative intensity of photostimulated emission and the digital Wiener spectra were calculated. The relative intensity of photostimulated emission decreased with increasing time, whereas Wiener spectral values showed no difference with increasing time. We concluded that noise properties were not affected by the fading of the IP in the CR system.     

Image quality and dose comparison among screen-film, computed, and CT scanned projection radiography: applications to CT urography.

PURPOSE: To evaluate image quality and dose for abdominal imaging techniques that could be used as part of a computed tomographic (CT) urographic examination: screen-film (S-F) radiography or computed radiography (CR), performed with moving and stationary grids, and CT scanned projection radiography (CT SPR). MATERIALS AND METHODS: An image quality phantom underwent imaging with moving and stationary grids with both a clinical S-F combination and CR plate. CT SPR was performed with six CT scanners at various milliampere second and kilovolt peak settings. Entrance skin exposure (ESE); spatial, contrast, and temporal resolutions; geometric accuracy; and artifacts were assessed. RESULTS: S-F or CR images, with either grid, provided image quality equivalent to that with the clinical standard, S-F with a moving grid. ESE values for both S-F and CR were 435 mR (112.2 microC/kg [1 mR = 0.258 microC/kg]) with a moving grid and 226 mR (58.3 microC/kg) with a stationary grid. All CT SPR images provided inferior spatial resolution compared with S-F or CR images. High-contrast objects generated substantial artifacts on CT SPR images. Compared with S-F, CR and CT SPR provided improved resolution of small low-contrast objects. The contrast between iodine and soft-tissue-mimicking structures on CT SPR images acquired at 80 kVp was twice that at 120 kVp. CT SPR images with acceptable noise levels required a midline ESE value of approximately 300 mR (77.4 microC/kg) at 80 kVp. CONCLUSION: S-F and CR provided better spatial resolution than did CT SPR. However, CT SPR provided improved low-contrast resolution compared with S-F, at exposures comparable to those used for S-F or CR.     

A quality control test of the image obtained with electronic portal imaging devices]

INTRODUCTION: A quality control of the digital image obtained from two electronic portal imaging devices is discussed. The devices are used to verify the radiotherapic treatment setup by comparing online images of the irradiated volume with those of the simulation devices. MATERIAL AND METHODS: Both iView and Target View devices, respectively installed on a dual energy SLi Precise Elekta and Saturne 42 Ge linear accelerators, consist of highly efficient phosphor screen and high quality videocamera, controlled by a workstation, able to generate digital portal images from few cGy doses. A phantom and software package are used to assess the spatial resolution and signal to noise ratio, and to compare tha data obtained. Spatial resolution and signal to noise ratio of both systems were studied as a function of energy, gantry angle and image acquisition parameters. RESULTS: The mean spatial resolutions obtained from the first 30 measurements were 0,265+/-0,012 and 0,220+/-0,010 lp/mm respectively for 6 and 18 MV of Saturne 42 (Target View) and 0,241+/-0,006 and 0,239+/-0,005 lp/mm for 4 and 6 MV of SLi (iView). Spatial resolution decreases as a function of energy, meanwhile there are no significant statistical differences as regards of the acquisition parameters; signal to noise ratio, instead, increases with integration time. Different values of the spatial resolution as a function of gantry angle are due to changes in the screen-camera distance and flexing of the detector housing. The quality control test is performed every 15 days by the technicians of our Radiotherapy Department. We set the reject level of spatial resolution and signal to noise ratio to be three standard deviations below the mean value obtained during the initial EPID characterization: if the measures fall below these values preventative maintenance is scheduled. CONCLUSIONS: The efficacy of the use electronic portal imaging devices for visualizing and quantifying the relative positions of anatomical structures within the radiation field depends on the image quality. It is therefore essential to devise quality control tests for the devices themselves, to guarantee an optimal level of system performance in a fast and efficient manner.