| 牛延涛,綦维维,张富利,燕树林,袁聿德.计算机X射线摄影系统与屏-片系统能量响应的对照研究[J].中华放射医学与防护杂志,2005,25(1):85-88 |
| 计算机X射线摄影系统与屏-片系统能量响应的对照研究 |
| A comparative study of energy responses of computed radiography system and screen-film system |
| 投稿时间：2004-09-18 |
| DOI： |
| 中文关键词: 计算机X射线摄影 X射线成像 自动曝光控制 |
| 英文关键词:Computed radiography X-ray imaging Automatic exposure control |
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| 中文摘要: |
| 目的 探讨计算机X射线摄影(CR)影像像素值与曝光因子(kVp和mAs)、被照体厚度的关系,传统屏片系统照片密度与曝光因子、被照体厚度的关系,并对两种能量响应的关系进行比较,为使用CR影像像素值和成像板(IP)平均入射照射量的测量值作为自动曝光控制系统的设定参数提供依据。方法 厚度为10、15、20cm的丙烯树脂板分别在50～90、70～120、90～140kVp和密度档为-2时成像,对照屏片系统与CR系统在不同管电压、相同被照体和密度档时的自动曝光响应。以上测试都使用滤线栅,用电离室测量IP的入射照射量。结果 在获得满足临床诊断要求的情况下,CR所需曝光量大约是高速屏片系统的2倍。CR系统的管电压像素值关系曲线与管电压照射量曲线相同。10cm被照体时,50～90kVp间的照片密度差值为1.21,像素差值为270;而20cm被照体时,90～130kVp间的密度差值为0.30,像素差值为600;15cm被照体时密度和像素差值居于两者之间,分别为0.62和160。结论 KodakCR900系统的感度值与中速屏片系统的感度比较接近。均匀野影像的曝光指示器值EI和IP照射量测量值可以用来设定自动曝光控制系统的光电计时器。屏片系统照片密度和CR影像像素值随kVp变化的规律以及两者的差异,对自动曝光控制系统的校准起参照作用。 |
| 英文摘要: |
| Objective To investigate the relationships between CR image pixel values and exposure factors (kVp,mAs), thickness of exposed subject, and those between conventional screen-film optical density and exposure factors (kVp,mAs), thickness of exposed subject. The relationships of these two kinds of energy response were compared. The feasibility of using CR image pixel values and measure values of IP mean incident exposure as parameters for setting up phototimer was studied. Methods Homogeneous acrylic phantoms 10, 15 and 20 cm thick were imaged with a traditional X-ray system and a CR system at 50-90, 70-120, 90-140 kVp and AEC density grade -2. Automatic exposure responses of the two systems at various tube voltages, same exposed subject thickness and grade selection were compared. Grid were used simultaneously for all radiography. Incident IP exposures were measured with an ionization chamber. Results Under the conditions of meeting clinical diagnostic requirements, the exposure of CR system was two times of that of rare earth screen-film system approximately. Tube voltages vs pixel value curves were similar to those of tube voltages vs exposure curves in CR system. When the thickness of the projected subject remained 10 cm, the screen- film density difference in 50-90 kVp was 1.21, and the pixel value difference was 270. When 20 cm thick, the density difference in 90-130 kVp was 0.30, and the pixel value difference was 100. When 15 cm thick, they were 0.62 and 160 seperately. Conclusion The speed value of Kodak CR 900 system is closely similar to that of medium screen-film systems. The exposure index value in flat field image and IP mean incident exposure could be used as factors to setup phototimer of AEC. The regularities between film density and kVp, pixel value and kVp, as well as differences in them, are important to the callibration of AEC system. |
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