数字X线摄影与双面阅读计算机X线摄影系统辐射剂量和影像质量的比较

Comparison of digital radiography and dual-sided reading of computed radiography system for imaging quality and radiation dose

目的对比研究DR与CR双面阅读成像系统辐射剂量与成像质量的关系。方法在相同的辐射剂量下用DR和CR双面阅读成像系统对ALVIM统计学摄影模体TRG进行曝光，记录摄影条件和模体表面入射剂量，然后固定此摄影条件kV值，选用不同mAs值（分别为3．2、4．0、4．3、4．8和5．2mAs）用CR双面阅读成像系统对模体进行曝光，记录表面入射剂量，并将所获取的影像在图像诊断工作站显示器上由3名影像医师进行视读打分，按照5分值判断法评判，绘制ROC曲线，计算每种信号的判断概率值（Pdet），对不同摄影系统及条件下3名观察者对模体影像信息的判断概率平均值采用双因素方差分析（ANOVA）进行比较。结果在辐射剂量为137．5μGy时，DR所摄取模体影像内容物中0．5～1．0mm直径骨代替物和0．9～2．0mm直径肌肉代替物的Pdet值分别是0．742～0．923和0．635—0．900，CR双面阅读成像系统所得模体影像内容物中上述直径的骨代替物和肌肉代替物的Pdet值分别是0．526—0．586和0．473～0．560；DR和CR双面阅读成像系统对不同直径的骨替代物ROC曲线Pdet相差为0．216～0．337，以直径1．0mm为著，相差0．337；二者对直径0．9～2．0mm的肌肉替代物相差为0．075～0．342，以直径2．0mm为著，相差0．342，差异有统计学意义（F=35．30，P〈0．01）。当CR双面阅读系统的摄影条件增为75kV、4．8mAs时，辐射剂量为180．4μGy，两种摄影系统所摄取影像ROC曲线的P。值基本相同，二者对直径0．5—1．0mm骨代替物ROC曲线的Pdet相差为-0．003～0．009；二者对直径0．9～2．0mm肌肉代替物ROC曲线的Pdet相差为-0．005—0．008，差异无统计学意义（F=5．23，P〉0．05）。在相同的判断概率值Pdet下，CR双面阅读成像系统所用表面入射剂量为180．4μGy，DR所用的表面入射剂量为137．5μGy。结论在相同曝光条件下，DR对模体内容物的检出率高于CR双面成像系统；在获得相似图像质量时，DR的辐射剂量低于CR双面阅读成像系统。

Objective To compare imaging quality and radiation dose on DR and dual-sided reading of CR system. Methods The TRG of ALVIM statistics phantom was exposed by DR and dual-sided reading of CR with the same radiation dose, then the exposure factor and the entrance surface close （ESD） were recorded. After that, the phantom was exposed by dual-sided reading of CR with various mAs （ 3.2, 4. 0,4. 3,4. 8 and 5.2 mAs） and the same kV, and the ESD was recorded ,too. The acquired images were read by three radiologists on the monitor of diagnosis work station with the same window width and window level, then the total points of the images were given with the method of a five-level confidence scale. ROC curves were drawn and probability Pdet was calculated. Then the data was analyzed statistically by analysis of variance （ANOVA）. Results The ROC analysis of bone substitute with diameter from 0. 5 to 1.0 mm and muscle substitute with diameter from 0. 9 to 2.0 mm showed A（z） values of 0. 742 to 0. 923 and 0. 635 to 0. 900 for DR system when the radiation dose was 137.5 μGy. The ROC analysis of bone substitute and muscle substitute showed A（z） values of 0. 526 to 0. 586 and 0. 473 to 0. 560 for dual-sided reading of CR at the same radiation dose. The probability Pdet discrepancy of bone substitute in two systems was from 0. 216 to 0. 337, with the highest of 0. 337 in the diameter of 1.0 mm. The probability Pdet discrepancy by muscle substitute in two systems was from 0. 075 to 0. 342, with the highest of 0. 342 in the diameter of 2. 0 mm. There was significant statistical difference between the two groups （ F = 35.30, P 〈 0. 01 ） . When the exposure factor of dual-sided reading of CR system was 75 kV,4. 8 mAs, the ESD was 180.4μGy, the ROC analysis in the bone substitute with diameter from 0. 5 to 1.0 mm and muscle substitute with diameter from 0. 9 to 2. 0 mm showed A（z） values was the same. The probability Pdet discrepancy of bone substitute in two systems was from - 0. 003 to 0. 009. The probability Pdet discrepancy of muscle substitute in two systems was from - 0. 005 to 0. 008, and there was no statistical difference between the two groups （ F = 5.23, P 〉 0.05）. When the probability Pdet of two systems was the same, the ESD was 180.4 μGY by dual-sided reading of CR system, and the ESD was 137.5 μGy by DR system. Conclusion Detection with DR system was proved to be superior to dual-sided reading of CR system at the same radiation dose. When the image quality was similar, the radiation dose of DR system was less than the dual-sided reading of CR system.