Effect of Computed Tomography Window Technique on the Results of Artificial Intelligence Classification of Lung Lesions
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摘要: 目的：应用3种不同的3D CNN的算法及5种CT窗口设置，探讨CT窗技术对人工智能分类肺部病变结果的影响。方法：回顾性分析172例周围型肺癌及185例局灶性肺炎的胸部CT影像资料，选择ResNet、ResNext以及DenseNet 3种不同的3D CNN的算法将病变分为两组，并在每1种3D CNN算法处理过程中应用5种不同的CT窗口设置，包括肺窗（1500，-600），纵隔窗（350，40），自定义窗口1（SW1）（1000，40），自定义窗口2（SW2）（1000，-100），全窗（4096，1024），分别计算分类准确率及AUC结果，并进行ROC曲线的两两对比。结果：ResNet的平均分类准确率最低为纵隔窗85.732％，AUC值为0.871；平均分类准确率最高为全窗，达91.596％，AUC值为0.946。ResNext的平均分类准确率最低为纵隔窗81.528％，AUC值为0.814；平均分类准确率最高为全窗，达86.568％，AUC值为0.882。DenseNet的平均分类准确率最低为纵隔窗87.954％，AUC值为0.906；平均分类准确率最高为SW2，达93.274％，AUC值为0.951。应用medcalc将3种3D CNN的5种窗口下的ROC曲线进行了两两对比发现，纵隔窗与肺窗、纵隔窗与SW1、纵隔窗与SW2之间的AUC值比较均有统计学意义。结论：3种3D CNN的分类诊断效能差别不大；CT窗口设置对CNN分类肺部病变结果有影响，在纵隔窗设置下以上3种人工智能算法对该两类肺部病变的诊断效能最差。Abstract: Objective: To use three different 3D CNN algorithms and five different computed tomography (CT) window settings to study the effect on the results of artificial intelligence classification of lung lesions in different CT window techniques. Method: A total of 172 cases of peripheral lung cancer and 185 of focal pneumonia who underwent chest CT were analyzed. Three different 3D CNN algorithms were selected (ResNet, ResNext, and DenseNet) to divide the lesions into two groups. Five different CT window settings, including lung window (1500, 600), mediastinal window (350, 40), custom window 1 (SW1) (1000, 40), and custom window 2 (SW2) (1000, 100), were used retrospectively. We calculated classification accuracy, receiver operating characteristic (ROC) curve, and area under the curve (AUC). The ROC curve was compared in pairs. Results: The average classification accuracy of ResNet was the lowest in the mediastinal window (85.732%; AUC value: 0.871) and the highest in the full window (91.596%; AUC value: 0.946). The average classification accuracy of ResNext was the lowest in the mediastinal window (81.528%; AUC value: 0.814) and the highest in the full window (86.568%; AUC value: 0.882). The average classification accuracy of DenseNet was the lowest in the mediastinal window (87.954%; AUC value: 0.906) and the highest in the SW2 window (93.274%; AUC value: 0.951). Medcalc was used to compare ROC curves under five windows of three 3D CNN. The AUC values between mediastinal window and lung window, mediastinal window and SW1, and mediastinal window and SW2 were statistically significant. Conclusion: There is little difference in the diagnostic efficacy of the three 3D CNN. Different CT window settings have an influence on the results of CNN classification of the lung lesions, and the diagnostic efficiency of the three 3D CNN is the worst under the mediastinal window.
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Keywords:
- artificial intelligence /
- CT window technique /
- 3D CNN /
- lung lesions
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图 1 不同窗口设置时对病灶的显示不同：（a）～（e）左肺上叶周围型肺癌（腺癌）；（f）～（j）右肺下叶局灶性肺炎
（a）和（f）肺窗；（b）和（g）纵隔窗；（c）和（h）SW1；（d）和（i）SW2；（e）和（j）全窗
Figure 1. Different display of lesions in different windows: (a)~(e) is the same patient, diagnosed as peripheral lung cancer in the upper lobe of the left lung (pathological examination shows adenocarcinoma); (f)~(j) is the same patient, diagnosed as focal pneumonia in the lower lobe of the right lung
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图 2 3D ResNet网络构建
主干使用18层的3D ResNet网络，在每个卷积块中，有1个卷积层（其参数在图中列出）、1个批标准化（Batch Normalization）层和1个ReLu激活层，图中的第1个参数“3×3×3”表示3D内核大小，第3个参数“64、128、256、512”表示通道数，最后1个参数“/2”表示步长为2的池层。
Figure 2. 3D ResNet network design
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表 1 ResNet 5个窗口设置的5倍交叉验证的分类准确率（％）及AUC结果
Table 1 Classification accuracy (%) and AUC results of 5-fold cross validation of 5 window settings in ResNet
窗口 （WW，WL） Fold 1 Fold 2 Fold 3 Fold 4 Fold 5 平均分类准确率/％ AUC 肺窗 （1500，−600） 87.50 88.73 91.55 91.55 93.06 90.478 0.929 纵隔窗 （350，40） 80.56 87.32 90.14 85.92 84.72 85.732 0.871 SW1 （1000，40） 86.11 92.96 88.73 91.55 90.28 89.926 0.918 SW2 （1000，−100） 87.50 92.96 90.14 91.55 90.28 90.486 0.923 Full （4096，1024） 87.50 90.14 90.14 94.37 95.83 91.596 0.946 
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表 2 ResNext 5个窗口设置的5倍交叉验证的分类准确率（％）及AUC结果
Table 2 Classification accuracy (%) and AUC results of 5-fold cross validation of 5 window settings in ResNext
窗口 （WW，WL） Fold 1 Fold 2 Fold 3 Fold 4 Fold 5 平均分类准确率/％ AUC 肺窗 （1500，−600） 84.72 80.14 87.32 88.73 87.50 85.682 0.896 纵隔窗 （350，40） 77.78 83.10 81.69 84.51 80.56 81.528 0.814 SW1 （1000，40） 86.11 85.92 88.73 85.92 84.72 86.280 0.881 SW2 （1000，−100） 84.72 88.73 83.10 85.92 87.50 85.994 0.878 Full （4096，1024） 83.33 91.55 85.92 87.32 84.72 86.568 0.882
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表 3 DenseNet 5个窗口设置的5倍交叉验证的分类准确率（％）及AUC结果
Table 3 Classification accuracy (%) and AUC results of 5-fold cross validation of 5 window settings in DenseNet
窗口 （WW，WL） Fold 1 Fold 2 Fold 3 Fold 4 Fold 5 平均分类准确率/％ AUC 肺窗 （1500，−600） 87.50 91.55 92.96 94.37 93.06 91.888 0.944 纵隔窗 （350，40） 88.89 87.32 91.55 84.51 87.50 87.954 0.906 SW1 （1000，40） 94.44 94.37 90.14 90.14 93.06 92.430 0.932 SW2 （1000，−100） 93.06 95.77 91.55 91.55 94.44 93.274 0.951 Full （4096，1024） 91.67 92.96 90.14 94.37 94.44 92.716 0.941
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