床旁胸部X射线摄影曝光指数的应用探讨

摘要

目的 探讨数字化X射线摄影(digital radiography,DR)床旁胸片曝光指数(exposure index,EI)与相关因数(kVp、mAs、SID、体厚)的变化规律性,指导床旁胸部DR摄影参数的合理应用.方法 分别固定影响El的3个可变参数kVp、mAs和SID中的某一项,对水模正后方的平板探测器进行同参数多次曝光,测得某一固定体厚(水模)下曝光指数随另外2个条件的变化规律.然后,固定前3个物理条件,再用层厚可变的亚克力板(acrylic,特殊处理的有机玻璃)模拟人体胸部正位的体厚,测量曝光指数随亚克力板厚度的变化规律.结果 在水模厚度固定为15cm的情况下,为使曝光指数基本不变,测得的3组数据表明:①当管电压被固定为某一定值,摄影距离增加的同时,应按曲线参数增加管电流;②当摄影距离被固定时,增加管电压的同时,应按曲线参数降低管电流;③当管电流被固定时,延长摄影距离的同时,应按曲线参数增加管电压,当这3个物理条件(kVp、mAs、SID)都固定时,曝光指数值随着亚克力板厚度的增加呈现出直线递减的规律.结论 适当曝光指数的应用既能保证数字化床旁摄影的图像质量,又能达到控制床旁摄影的照射剂量,相对降低受检者的辐射剂量的目的.%Objective To study the regularity of exposure index (El) and relative factors ( kVp, mAs, SID, body thickness) of bedside DR in order to guide reasonable application of radiographic factors. Methods One of the three variable parameters, kVp, mAs and SID, was fixed and Flat Panel Detector (KPD) behind water phantom was exposed many times in same exposure parameter. The change of El values over the other two parameters was measured at a certain body thickness (water phantom). After that, we used alterable-thickness Acrylic board to imitate the patients' body thickness. The change of El values over the Acrylic boards' thickness was measured. Results We fixed the water phantoms thickness in 15 cm to keep El unchanged. The three groups' data indicated; When kVp was fixed, mAs had to be increased based on curve parameters with the increase of SID; ? When the SID was fixed, mAs had to be reduced based on curve parameters with the increase of kVp; When mAs was fixed, kVp had to be increased based on curve -parameters with the increase of SID. When the three parameters (kVp, mAs, SID) were fixed, the El value showed a linear decreasing trend with increase of the Acrylic boards' thickness. Conclusion Suitable El can not only guarantee the image quality of bedside digital photography but also control radiation dose.