增感屏-胶片体系感光测定距离法的探讨  

Study of sensitometric distance method for screen film system

作　　者：燕树林[1] 李硕鹏[1] 赵波[1] 王建国[1] 

机构地区：[1]首都医科大学附属北京同仁医院放射科

出　　处：《中华放射学杂志》1998年第6期414-418,共5页Chinese Journal of Radiology

摘　　要：目的建立以焦点胶片距离的改变，取得Ｘ线阶段曝光的屏片体系感光测定方法。方法利用常规Ｘ线机在焦点胶片距离４０～３２０ｃｍ的范围内，取７个距离曝光点，对ＯｋａｍｏｔｏＤＭＳ（蓝屏）／ＦｕｊｉｎｅｗＲＸ（感蓝片）及ＦｕｊｉＨＲＲｅｇｕｌａｒ（绿屏）／ＦｕｊｉＨＲＮ（感绿片）两种屏片体系样本做感光测定，绘制特性曲线、斜率密度曲线，求取特性值。同时与感光仪和铝梯定量测定法（Ｂｏｏｔｓｔｒａｐ法）作比较。结果（１）测试用Ｘ线机的平均管电压值、高压纹波率、输出剂量、曝光时间等四项指标的变动系数均小于０．０２，重复性良好。（２）Ｘ线强度与距离平方在测试距离内呈线性关系，倾斜值为－２．０４，证明本实验中的“距离反平方定律”成立。（３）实验证明，距离法的曝光条件确定在６０～８０ｋＶｐ，ｍＡｓ以在距离８０．３ｃｍ［相对曝光量对数（ＬｏｇＲＥ）＝１．２］时得到２．０＋本底灰雾的密度值为调节指标，总滤过３．０ｍｍＡｌ＋０．５ｍｍＣｕ（三相工频机）或３．５ｍｍＡｌ（中频机）。结论距离法与感光仪法、时间阶段曝光法、铝梯定量法相比，重复性较好，曝光机制符合Ｘ线摄影实际，便于统一。Purpose To establish a screen film system sensitometric method of X ray scale exposure by changing the distance between focus and film. Methods Using conventional X ray equipments, with distance ranging from 40cm to 320cm,we selected seven distance exposure points and made sensitometry for two types of screen film system patterns(Okamoto DMS/Fuji new RX and Fuji HR Regular/Fuji HR N) and plot characteristic curves, gradient density curves and acquired characteristic values. At the same time, it was compared with sensitometer method and bootstrap method. Results (1) Variability indexes of average X ray tube kilovoltage , high voltage wave rate,output dose,exposure time etc, of the tested X ray equipment were below 0.02 with good reproducibility. (2) X ray intensity was linearly related to the distance squared in the measured disance.The gradient was -2.04 confirming the validity of “disance inverse square law” in this experiment. (3) The experiment confirmed that exposure conditions of distance method were set at 60 - 80kVp, mAs was adjusted based on the density of 2.00+base fog acquired at the distance of 80.3cm(LogE=1.2), gross filters of 3.0mmAl+ 0.5mmCu (3 phase low frequency equipment) or 3.5mmAl(medium frequency equipment). Conclusion Compared to sensitometre method,time scale exposure method and bootstrap method, the reproducibility and exposure mechanism of the distance method are better and accord with radiologic practice, being more practical for unification.

关 键 词：光密度测定法 放射摄影术 X线增感屏 

分 类 号：R814[医药卫生—影像医学与核医学]