The Comparative Study Of HRCT And ～(18)F-FDG PET/CT In The Evaluation Of Solitary Pulmonary Nodules

Objective: To comparatively evaluate the single role and to discuss the feasibility of combining application in diagnosis of solitary pulmonary nodules (SPNs) with HRCT and ¹⁸F-FDG PET/CT by the study of 47 casesMaterials and Methods: 47 solitary pulmonary nodules were examined with ¹⁸F-FDG PET/CT and multi-slice helical CT high resolution scans (HRCT), all of which were proven pathologically or by follow-up. The examinations were performed solely by HRCT and ¹⁸F-FDG PET/CT at interval of a week. The multi-slice helical CT scans were carried out by GE LightSpeed 16 slices CT (GE Medical Systems, Milwaukee, Wis). All of the images were transmitted to the single workstation (Advantage Windows 4.1, GE Medical Systems), which were analyzed and reconstructed by MPVR (mutli-planar volume reconstructions). ¹⁸F-FDG PET/CT data were acquired by GE Discovery LS PET-CT system and the fused images were reconstructed by the workstation (GE Entegra). The HRCT images of SPNs were analyzed and graded by there senior radiological doctors on the basis of morphological characters. ¹⁸F-FDG PET/CT data were evaluated semi-quantitatively on the basis of the contrast radio (CR) obtained as follows. The regions of interest(ROIs) placed in the nodules and contralateral lung. Highest activities in the tumor ROI (T) and in the contralateral normal lung ROI (N) were measured. The CR was calculated by (T-N)/(T+N) in each nodule as an index of FDG uptake. Receiver operating characteristics (ROC) curve was respectively constructed according to the HRCT score and the CR value and the cut-off values were determined for diagnosis of malignancy. Retrospective analysis showed the optimal HRCT cut-off value to be 3.5 and the optimal 18F-FDG PET/CT cut-off value to be 0.4. Therefore, SPNs with CT score^3.5 were defined as positive for HRCT and those with CT score<3.5 as negative, and SPNs with CR^0.4 were defined as positive for FDG-PET and those with CR<0.4 as negative. The results of HRCT and FDG-PET/CT were compared with pathological and follow-up results respectively. Positive HRCT and FDG-PET findings with malignancy and benign nodules were defined as true positive (TP) and false positive (FP), respectively. Negative HRCT and FDG-PET findings with malignancy and benign nodules were defined as false negative (FN) and true negative (TN), respectively. The diagnostic values of HRCT and FDG-PET were assessed by calculating sensitivity, specificity, accuracy, positive and negative predictive value. Sensitivity was calculated as TP/TP+FN, specificity as TN/TN+FP, accuracy as TP+TN/SPNs, positive predictive value as TP/TP+FP, and negative predictive value as TN/TN+FN. All data were analyzed for significance by using the x2-test. Values of P<0.05 were accepted as significance.Results: There were 25 malignant nodules and 22 benign nodules in the 47 SPNs. All of malignant nodules were pathologically confirmed as lung cancer, in which there are 20 adenocarcinnma (including 2 alveolar cell carcinomas and 1 scar carcinomas), 3 squamous carcinomas, 1 small cell carcinoma and 1 big cell carcinoma. In all 22 benign nodules, 6 nodules were pathologically proved as tuberculomas (TB), 1 nodule as inflammatory pseudotumor, 2 nodule as cryptococcosis, 6 nodules as chronic pneumonia, and 7 nodules were proved as benign by 16-24 months' follow-up. In HRCT results, 21 of 25 malignant nodules were diagnosed as positive (TP) and 4 as negative (FN), and 1 of 22 benign nodules was diagnosed as positive (FP) and 21as negative (TN). In FDG-PET results, 23 of 25 malignant nodules were diagnosed as positive (TP) and 2 as negative (FN), and 4 of 22 benign nodules were diagnosed as positive (FP) and 18 as negative (TN). The sensitivity, specificity, accuracy, positive and negative predictive value of HRCT prediction were 84.00%, 95.45%, 89.36%, 95.45%, 84.00%. The sensitivity, specificity, accuracy, positive and negative predictive value of FDG-PET prediction were 92.00%, 81.81%, 87.23%, 85.19%, 90.00% respectively. To evaluate SPN, HRCT and FDG-PET did not have significant difference in accuracy , P>0.05, but there were significant differences in sensitivity, specificity, positive and negative predictive value, P<0.05. The sensitivity and negative predictive value of FDG-PET were much better than HRCT, but the specificity and positive predictive value were less than HRCT. There were 4 malignant nodules in 5 SPNs falsely diagnosed by HRCT, in which the sizes of 3 nodules were less than 1.0cm. There were 4 benign nodules in 6 SPNs falsely diagnosed by I8F-FDG PET/CT, and the sizes of 4 nodules were 1.0-3.0cm. 1 malignant SPN less than 1.0cm in size and 1 benign SPN 1.0-3.0cm in size were falsely diagnosed by HRCT and 18F-FDG PET/CT synchronously. To evaluate the 43 SPNs 1.0-3.0cm in size, the sensitivity, specificity, accuracy, positive and negative predictive value of HRCT and 18F-FDG PET/CT prediction were 95.45%, 95.24%, 95.35%, 95.45%, 95.24% and 95.45%, 80.95%, 88.37%, 84.00%, 94.44% respectively. The sensitivity and negative predictive value of 18F-FDG PET/CT and HRCT were almost equal, P>0.05 and the specificity, accuracy and positive predictive value of 18F-FDG PET/CT were less than HRCT, P<0.05. To compare with the data of HRCT and PET/CT in the evaluation of all 47 SPNs, the specificity and negative predictive value of HRCT were higher than that of 43 SPNs 1.0-3.0 cm in size evaluated by HRCT, P<0.05, and the other data were not obviously changed, P>0.05.Conclusion: The values of HRCT and 18F-FDG PET/CT were obvious in the evaluation of solitary pulmonary nodule (SPN). However, the characters of SPN have overlaps in the qualitatively different nodules. The majority of 1.0-3.0cm size SPNs are characteristic on HRCT, especially with MPVR. 18F-FDG PET/CT plays a veryimportant role in the SPN not to be definitely diagnosed by HRCT. The sensitivity and negative predictive value of 18F-FDG PET/CT were relatively high, and the radioactive uptake of malignant nodule is obviously high to benign one. If FDG uptake of one SPN is very low, the SPN may be diagnosed as benign to a great degree. To accidentally found SPN of less than 1 .Ocm in size, the possibility of malignancy is not decidedly excluded even if the I8F-FDG PET/CT result is negative, and it is need to combine with the result of HRCT for to decide the necessity of short-term follow-up of operation. The specificity and positive predictive value of ' F-FDG PET/CT were less than HRCT. When the FDG uptake of SPN is a little high and F-FDG PET/CT result is positive, especially to the SPN of larger than 1.0cm in size, the diagnosis of malignancy need to be carefully affirmed and the accuracy of diagnosis can be increased by combining with HRCT. 18F-FDG PET/CT can find the early metastasis unfound on CT. Therefore, when the SPN found on CXR or CT cannot be completely excluded the possibility of malignancy, I8F-FDG PET/CT may largely help to determine the nature...