Comparison Study Of ¹⁸F-FDG PET/CT With Enhanced CT In The Diagnosis Of Solitary Pulmonary Nodules

Objective:PET/CT and enhanced CT are commonly used in the diagnosis of solitary pulmonary nodules.Whether it is ¹⁸F-FDG（18-fluorodexyglucose）PET/CT or enhanced CT,the differential diagnosis of solitary pulmonary nodules is still one of the clinical problems.In this study,the diagnostic efficacy of ¹⁸F-FDG PET/CT in solitary pulmonary nodules was compared with enhanced CT,and to explore the diagnostic value of the combined diagnosis of solitary pulmonary nodule in order to improve the diagnostic level of single pulmonary nodule.Methods:1. A retrospective analysis was performed on 189 patients with solitary pulmonary nodules initially diagnosed in hospital from January 2016 to May2019.Inclusion criteria:（1）The diameter of pulmonary nodules confirmed by CT≥8 mm,（2）Patients haven’t received radiotherapy,chemotherapy,surgery and other treatment before the examination.Exclusion criteria:（1）The patients wtih asiatic or ground glass pulmonary nodules,（2）Patients haven’t other history of malignant tumors.2.¹⁸F-FDG PET/CT imaging was performed after intravenous injection of ¹⁸F-FDG 222～492.1 MBq（6～13.3 m Ci）for 50～60 min,and Maximum Standard Uptake Value(SUV_max)of pulmonary nodules was measured.When PET or CT images of pulmonary nodules were inconclusive,delayed chest imaging was performed after ¹⁸F-FDG injection for 120 min.And delayed SUV_max was measured and△SUV_max was calculated.3. Enhanced CT imaging.Pulmonary CT scan was performed first,and arterial phase enhanced CT scan was performed after the injection of iohexanol 90～120 m L for 30s.The plain CT value and enhanced CT value of pulmonary nodules were measured,and the enhancement peak value was calculated.The performer interval of PET/CT and enhanced CT was within one week.4. Diagnostic criteria.4.1 ¹⁸F-FDG PET/CT diagnostic criteria:when there are malignant signs of solitary pulmonary nodules on the CT image,such as（burr sign,lobular sign,pleural depression,bronchial truncation sign,vascular immobilization sign）,and solitary pulmonary nodules on the PET image are FDG-avid,or △SUV_maxrise,the diagnosis is malignant pulmonary nodules.When the pulmonary nodules on the CT image show benign signs such as round smooth surface or calcification,and no FDG-avid in solitary pulmonary nodules on PET images,or FDG-avid on it but△SUVmax no change or descend,the diagnosis is benign pulmonary nodules.4.2 Enhanced CT diagnostic criteria:when the solitary pulmonary nodules on the CT images presented malignant signs or the peak of enhanced CT scan was>15HU,the diagnosis is malignant pulmonary nodules.When the solitary pulmonary nodules on the CT images presented benign signs or the peak of enhanced CT scan was≤15HU,the diagnosis is benign pulmonary nodules.4.3 Diagnostic criteria of ¹⁸F-FDG PET/CT combined with enhanced CT: when PET/CT imaging was consistent with enhanced CT results,the combined diagnosis was benign or malignant pulmonary nodules.When the PET/CT imaging diagnosis was pulmonary malignant but the enhanced CT diagnosis was benign,the combined diagnosis was benign pulmonary nodules.When PET/CT was diagnosed as pulmonary benign but enhanced CT as malignant,the combined diagnosis was pulmonary benign nodules.5. Comparison of the diagnostic efficacy of ¹⁸F-FDG PET/CT,enhanced CT and combined diagnosis for solitary pulmonary nodules.5.1 The sensitivity,specificity,accuracy,positive predictive value（PPV） and negative predictive value（NPV）of PET/CT,enhanced CT and combined diagnosis in the diagnosis of solitary pulmonary nodule were calculated respectively.5.2 Comparison of the diagnostic efficacy of PET/CT,enhanced CT and combined diagnosis for solitary pulmonary nodules.5.3 According to nodules length（L）,they were divided into three groups: group A was L≤1cm,group B was 1cm<L≤2cm,and group C was 2cm<L≤3cm.The sensitivity,specificity and accuracy of PET/CT imaging and enhanced CT for solitary pulmonary nodules in three groups were calculated respectively.The sensitivity,specificity and accuracy of PET/CT imaging and enhanced CT in the diagnosis of solitary pulmonary nodules were compared among the three groups.5.4 The optimal thresholds of△SUV_max and enhanced peak diagnosis solitary pulmonary malignant nodules were calculated respectively.6. Statistical analysis:SPSS 24.0 statistical analysis software was used for data processing and analysis.The diagnostic results of PET/CT imaging,enhanced CT and combined diagnosis were compared byχ² test.The diagnosis results of PET/CT in group A,B and C were compared with those of enhanced CT diagnosis using Fisher’s exact test orχ² test.Receiver Operating Characteristic（ROC）curves were used to calculate the optimal threshold for diagnosis of solitary pulmonary malignant nodules.P<0.05 was defined as statistically significant.Results:1.Among 189 patients with solitary pulmonary nodules,there were 136cases of malignant nodules and 53 cases of benign nodules.2.The sensitivity of ¹⁸F-FDG PET/CT,enhanced CT and combined diagnosis methods in the diagnosis of solitary pulmonary malignant nodules were 97.6%（132/136）,87.5%（119/136）and 86.0%（117/136）,respectively,the specificity were 69.8%（37/53）,67.9%（36/53）and 86.8%（46/53）,repectively,the accuracy were 89.4%（169/189）,82.0%（155/189）and 86.2%（163/189）,and the PPV were 89.2%（132/148）,87.5%（119/136）and 94.4%（117/124）repectively,the NPV were 90.2%（37/41）,67.9%（36/53）and70.8%（46/65）,respectively.3.The sensitivity,accuracy and NPV of ¹⁸F-FDG PET/CT in the diagnosis of solitary pulmonary malignant nodules were higher than those of enhanced CT,with statistical difference（χ² value:4.235～8.721,all P<0.05）,and there were no statistical difference in the diagnosis specificity and PPV（χ²value:0.044、0.197,all P>0.05）.4.Compared with ¹⁸F-FDG PET/CT imaging alone,combined with enhanced CT in the diagnosis of solitary malignant nodules in the lung,the diagnostic specificity was higher,the sensitivity and NPV were lower,and the differences were statistically significant（χ² value:4.498～10.686,all P<0.05）,and there were no significantly different for the diagnostic accuracy and PPV（χ² value:1.784、3.296,all P>0.05）.The specificity of ¹⁸F-FDG PET/CT combined with enhanced CT in the diagnosis of solitary malignant nodules in the lung was better than that of single enhanced CT,the difference was statistically significant（χ² value:5.386,P<0.05）,but there were no statistically significant difference for sensitivity,accuracy,PPV and NPV（χ² value:0.111～3.638,P>0.05）.5.Group A（L≤1cm）:the sensitivity,specificity and accuracy of ¹⁸F-FDG PET/CT for solitary pulmonary malignant nodules were not significantly different from that of enhanced CT（all P>0.05）.Group B（1cm<L≤2cm）:the sensitivity of ¹⁸F-FDG PET/CT were higher than that of enhanced CT（χ²value:6.767,P<0.05）.The specificity and accuracy,no statistical difference（χ² value:0.081、3.663,all P>0.05）.Group C（2cm<L≤3cm）:the sensitivity,specificity and accuracy of ¹⁸F-FDG PET/CT for solitary pulmonary nodules were not significantly different from that of enhanced CT（χ² values:0.125～2.043,all P<0.05）.6. The optimal threshold for△SUVmax to diagnose solitary pulmonary malignant nodules was 1.58%,the diagnostic sensitivity was 95.2%（79/83）,the specificity was 62.5%（25/40）,the accuracy was 84.6%（104/123）,the PPV was 84.0%（79/94）and the NPV was 86.2%（25/29）,repectively.7. The optimal threshold of enhanced CT peak value for the diagnosis of solitary pulmonary malignant nodules was 14.8HU,the diagnostic sensitivity was 73.5%（100/136）,the specificity was 62.3%（33/53）,the accuracy was70.4%（133/189）,the PPV was 84.3%（100/120）and the NPV was47.8%（33/69）,repectively.Conclusion:1.¹⁸F-FDG PET/CT imaging has high sensitivity,accuracy,PPV and NPV in the diagnosis of solitary pulmonary malignant nodules.2.¹⁸F-FDG PET/CT imaging was superior to enhanced CT in the diagnosis of solitary pulmonary malignant nodules in terms of sensitivity,accuracy and NPV.The sensitivity of PET/CT imaging in the diagnosis of single malignant malignant nodules in the lung is higher than that of enhanced CT for pulmonary nodules with length and diameter between 1 and 2 cm.3.¹⁸F-FDG PET/CT imaging combined with enhanced CT is a comprehensive imaging diagnosis with information on anatomy,metabolism and blood supply of lesions,which is of high value in the diagnosis of solitary pulmonary malignant nodules.Compared with ¹⁸F-FDG PET/CT,combined diagnosis could improve its diagnostic specificity.4.The optimal threshold of△SUV_maxfor diagnosis of solitary pulmonary malignant nodules in ¹⁸F-FDG PET/CT has certain reference value,but it can not be used as the basis for diagnosis.the enhanced CT peak>14.8 HU,the diagnosis has a high positive predictive value for lung malignant nodules.