观片灯亮度对数字影像照片诊断效能影响的实验研究

An experimental study regarding diagnostic accuracy on image interpretation of the digital image film by using viewboxes of different luminance

目的了解不同亮度观片灯对数字影像照片诊断准确性的影响。方法测量临床实际工作环境中用到的所有观片灯，然后选出3个作为研究观片灯，分别代表高、中、低亮度，计算平均亮度值。应用Kodak DR 3000，曝光参数为75kV、3．2mAs，焦片距100cm，对统计学摄影体模（TRG）进行摄影，获得体模影像照片。将该照片分别置于上述3种不同亮度的观片灯上，由3名医学影像科医师进行视读，用5值判断法获得信号和噪声的记分，计算出TRG模体中骨替代物和肌肉替代物的真阳性概率[P（S／s）]和假阳性概率[P（S／n）]值，绘制ROC曲线，并计算其准确性的判断概率值（Pdet）。采用配对t检验比较对不同亮度的观片灯的Pdet值。结果3种观片灯的平均亮度值分别为（3489±256）、（2231±220）、（816±168）cd／m^2。当骨替代物直径分别为0．6、0．7、0．8mm，在高亮度观片灯上得到的Pdet值分别为0．558±0．009、0．788±0．008及0．813±0．006；中等亮度的观片灯的Pdet值分别为0．525±0．013、0．713±0．013及0．775±0．016；在低亮度观片灯上得到的Pdet值分别为0．475±0．022、0．550±0．018及0．688±0．020。肌肉替代物直径分别为0．9、1．0、1．2mm时，在高亮度观片灯上，Pdet值分别为0．663±0．010、0．750±0．008及0．933±0．005；中等亮度观片灯上，得到的Pdet值分别为0．613±0．019、0．650±0．013及0．850±0．019；低亮度观片灯上，得到的Pdet分别为0．550±0．025、0．575±0．021及0．725±0．016，高亮度组与中亮度组、中亮度组与低亮度组之间分别进行配对t检验，差异均有统计学意义（t值分别为5．057和4．681，P〈0．05）。结论观片灯的亮度可影响诊断的准确性，观片灯的亮度越高，观察到的影像信息越丰富，诊断的准确性越高。

Objective To evaluate diagnostic accuracy of image interpretation using viewboxes at different luminance with ALVIM statistical phantom （TRG）. Methods A digital film of TRG image was obtained by exposing the phantom of TRG with Kodak DR 3000 using proper parameter. Viewboxes with three different luminance were selected from those used in daily work. The film of TRG was evaluated with these viewboxes of three different luminance by three different radiologists with experience of five, eight and sixteen years respectively. A grade scale of 5 was used to evaluate each row of signal and noise. According to the results and formula, the probabilities of true-positive [ P （S/s） ], false-positive [ P （S/n） ] and true answer（ Pdet ） were obtained. Results The three kinds of luminance used in viewboxes were： （3489 ± 256）, （2231 ± 220） , （816 ± 168 ） cd/m^2. When the average luminance of viewbox was 3489 cd/m^2, Pdet of 0. 6,0. 7,0. 8 mm in bone substitute was 0. 558 ± 0. 009, 0. 788 - 0. 008, 0. 813 - 0. 006, 19det of 0. 9, 1.0,1.2 mm in muscle substitute was 0. 663 ±0. 010, 0. 750 ±0. 008, 0. 933 ±0. 005; When the average luminance of viewbox was 2231 cd/m^2, Pdet of 0. 6,0. 7,0. 8 mm in bone substitute was 0. 525 ± 0. 013, 0. 713 ±0. 013,0. 775 ±0. 016 ,Pdet of 0. 9,1.0,1.2 mm in muscle substitute was 0. 613 ± 0. 019,0. 650 ± 0. 013,0. 850 ±0. 019;When the average luminance of viewbox was 816 cd/m^2 , Pdet of 0. 6,0. 7,0. 8 mm in bone substitute was 0. 475 ± 0. 022,0. 550 ± 0. 018,0. 688 ± 0. 020, Pdet of 0. 9,1.0, 1.2 mm in muscle substitute was 0. 550 ± 0. 025,0. 575 ± 0. 021, O. 725 ± 0. 016. Viewboxes of different luminance were compared to one another by paired t-test. The results of comparison all had significant statistical differences （ t = 5. 057 and 4. 681 ,P 〈 0. 05 ）. Conclusions The image displayed by viewboxes at different luminancehad significant influence on image interpretation. The higher the luminace of viewbox, the richer the information displayed, and the higher the accuracy of diagnosis.