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目的探讨数字X线摄影系统焦点至探测器距离(FFD)的设定对体模体表入射剂量(ESD)的影响。方法利用BMD Phantom Spine Femur模拟人体进行数字X线摄影。根据预设管电压分为60、80、120 k V 3组,每组仅以FFD为变量进行分次曝光。采用自动曝光(AEC)模式,去除滤线器,固定照射野15 cm×15 cm,每次曝光中探测器获得相同曝光量。GE DEFINIUM 6000功能数字化摄影系统电离室自动测量ESD,MARK标记评价影像畸变率。采用SPSS 19.0软件作Pearson相关分析,建立体表入射剂量与FFD的关系曲线。结果在探测器感光相同时,ESD与FFD呈负相关(r=-0.922,P<0.01),FFD从100 cm增至200 cm,在60、80、120 k V时,ESD值分别降低了35.4%、35.3%、44.0%。60、80、120 k V时影像畸变率无变化,FFD 200 cm在不同管电压时影像畸变率均明显低于FFD 100 cm(P均<0.05)。结论增加FFD可以降低受检者的辐射剂量,改善几何成像性能。
Objective To investigate the effect of FFD setting on phantom body surface dose (ESD) in digital radiography. Methods BMD Phantom Spine Femur was used to simulate the human body for digital radiography. According to the preset tube voltage is divided into 60,80,120 k V 3 groups, each group only FFD variables for sub-exposure. With automatic exposure (AEC) mode, the filter was removed and the field of exposure was fixed 15 cm × 15 cm with the same amount of exposure for each exposure. GE DEFINIUM 6000 FUNCTIONAL DIGITAL CAMERA SYSTEM Ionization Chamber Automated Measurement of ESD and MARK Marks for Image Distortion. SPSS 19.0 software was used for Pearson correlation analysis to establish the relationship between body surface dose and FFD. The results showed that ESD was negatively correlated with FFD (r = -0.922, P <0.01) and FFD increased from 100 cm to 200 cm at the same sensitivities of the detector. ESD values were reduced by 35.4 at 60, 80 and 120 kV %, 35.3%, 44.0%. At 60, 80 and 120 kV, the image distortion rate did not change. The image distortion rate of FFD 200 cm at different tube voltages was significantly lower than that of FFD 100 cm (all P <0.05). Conclusion Increasing FFD can reduce the dose of radiation and improve the imaging performance.