移动数字X线摄影条件对胸部影像质量的影响

摘要

目的 探讨不同的摄影管电压和毫安秒对图像感兴趣区内像素值均值、噪声及对比度噪声比的影响,以寻找最适合的摄影条件,在获得较好的图像质量的前提下,减少患者的辐射剂量.方法 根据摄影参数的不同,分为两个实验组:第一组保持毫安秒不变(普通床边胸片的毫安秒条件),将管电压从55 kVp升至120 kVp,每5 kVp为1档.从第一组中选择出图像质量较好的四种管电压,改变毫安秒,从1.00 mAs至5.00 mAs共7档,作为第二实验组.测量并记录2个密度区内感兴趣区像素值均值和噪声值,计算对比度噪声比.结果 感兴趣区像素值均值基本不随管电压和毫安秒的变化而改变.管电压对各个区域的噪声值均有影响:<80 kVp时,噪声值随管电压的升高显著减小,对比度噪声比明显升高;≥80 kVp时,管电压的升高对各个区域噪声值的影响较小,对比度噪声比变化也较小.四种管电压固定的情况下,毫安秒对各个区域的噪声值均有影响:<2.00 mAs时,噪声值随毫安秒的升高显著减小,对比度噪声比明显升高;≥2.00 mAs时,毫安秒的升高对各区域噪声值的影响越来越小,对比度噪声比变化也较小.结论 胸部数字X线摄影的推荐管电压为75～85 kVp,根据患者的体型进行选择;推荐的毫安秒为2.00～3.00 mAs,既可获得比较好的图像质量,又可使患者接受较少的X线辐射剂量.%Objective To assess the impact of different exposure tuhe voltage and mAs on pixel mean value , noise and contrast to noise ratio (CNR) of image in regions of interest , in order to recommend the best exposure parameters to reduce radiation dose on the condition of good image quality . Methods One group kept the mAs constantly (the mAs was used in conventional bedside X-ray photography ) and raised the tube voltage from 55 kVp to 120 kVp hy step of 5 kVp . Four suitable kVp values were selected out from first experiment and the mAs was raised from 1. 00 to 5 by 7 .00 steps as the second experiment . The pixel mean value and noise of the image in region of interest were measured and recorded in 2 density areas , and the CNR was calculated . Results The pixel mean value of the image in region of interest was not influenced by the exposure tube voltage or mAs . The exposure condition affected the noise and CNR : When tube voltage was ＜80 kVp , the noise decreased and CNR remarkably as tube voltage raised . When tuhe voltage was ≥80 kVp , increase of tube voltage affected the noise and CNR indistinctly . Keeping the tuhe valtage in 4 different values , the mAs influenced the noise and CNR : When mAs was ＜ 2. 00 , the noise decreased remarkably as the mAs raised . When mAs was ≥2. 00 , raising mAs affected less and less on the noise and CNR . Conclusion The suggested tube voltage of the chest radiography by DR is from 75 kVp to 85 kVp , depending on patients′form , and the suggested mAs is from 2. 00 to 3. 00 for ohtaining better image quality and less patients ′ X- ray dose .