摘要目的 研究腰椎数字化X射线摄影(DR)的焦点至探测器距离(FFD)与体表入射剂量(ESD)的相关性,探讨FFD对辐射防护的价值.方法 采用自动曝光模式(AEC)对腰椎骨密度(BMD)校准体模模拟腰椎正侧位DR摄影;去除滤线栅,参考腰椎常用摄影管电压,分别设定管电压为70和90 kV;改变FFD自100～240 cm范围内以10 cm递增,FFD共改变15次.德国QUART dido 2100K型X射线剂量仪测量相关参数.Excel建立体模ESD、管电流、曝光指数(EI)与FFD关系曲线;SPSS 19.0作Pearson相关分析及回归分析.结果 (1)管电压70 kV时:FFD与ESD负相关(r=-0.922,P＜0.001);FFD与管电流正相关(r=0.991,P＜0.001);EI与FFD负相关(r=-0.938,P＜0.001).(2)管电压90 kV时:FFD与ESD负相关(r=-0.955,P＜0.001);FFD与管电流正相关(r =0.994,P＜0.001);FFD与EI无相关(r=-0.523,P=0.051).(3)不同管电压相关系数的差异性分析显示,FFD与ESD及管电流的相关性差异均无统计学意义.(4)管电压70 kV时FFD与ESD值的回归方程:y=-0.805x+319.731(F=74.175,P＜0.001);管电压80 kV时FFD与ESD的回归方程:y=-3.152x+457.613(F=133.524,P＜0.001).结论 在DR摄影AEC曝光模式下,探测器获得相同曝光量时,FFD与ESD在腰椎X射线摄影中高度负相关.增加FFD可以有效减少腰椎DR摄影的ESD,利于辐射防护.

abstractsObjective To investigated the correlation between the focus-to-flat panel detector distance and entrance surface dosed in digital radiography of lumbar spine.Methods The spine phantom used for bone mineral density(BMD) calibration was radiographed at different value of FFD (100 ～ 240 cm with the interval 10 cm,totally 15 times) using 70 kV and 90 kV with the automatic exposure control (AEC) mode without anti-scatter grid.The parameters measured by QUART dido 2100K type X-ray dose meter.So record the value parameters of the tube current (mAs) and entrance surface dose (ESD).The relation curve were counted between FFD,ESD,mAs and Exposure index (EI) use excle.Pearson correlation analysis and related coefficient difference analysis were performed using the SPSS 19.0 software (P ＜0.05 for the statistically significant level).The FFD and ESD values of regression equation were obtained with regression analysis.Results (1) When the tube voltage was 70 kV:FFD and ESD were negative correlation (r =-0.922,P ＜ 0.001),FFD and mAs were positive correlation (r =0.991,P ＜0.001),FFD and EI negative correlation (r =-0.938,P ＜ 0.001).(2) When the tube voltage was 90 kV:FFD and ESDwere negative correlation (r=-0.955,P ＜0.001),FFD and mAs were positive correlation (r=0.994,P ＜0.001),FFD and EI showed no significant correlation (r=-0.523,P＞0.05).(3) Different position correlation coefficient analysis of the difference was not statistically significant difference.(4) The regression analysis results:The regression equation of the lumbar anteriorposterior position FFD and the ESD at 70 kV:y=0.805 x + 319.731 (F=74.175,P ＜0.001).The regression equation of the lumbar lateral position FFD and the ESD at 90 kV:y =3.152 x + 457.613 (F =133.524,P ＜ 0.001).Conclusions The FFD and ESD in the lumbar spine X-ray radiography were relevant and highly negative correlation.It can effectively reduce the radiographic ESD of lumbar spine with the increasing of the FFD.