Background: 18F-Fluorodeoxyglucose-positron emission tomography (18F-FDG-PET) is a very useful imaging technique and is the best modality for the evaluation of many kinds of tumour. However, in the evaluation of hepatocellular carcinoma (HCC), the diagnostic accuracy of routine 60 min static imaging is not satisfactory. Some authors have suggested that delayed 2 h imaging is a better 18F-FDG-PET protocol for tumour detection. However, the value of delayed 3 h imaging has not been clarified. In this study, we performed delayed 2 h and 3 h imaging on patients with HCC and compared their diagnostic accuracy with standard 60 min imaging.
Methods: Twelve patients with HCC were enrolled in this study. Of these 12 patients, four had not been treated and eight had received transcatheter arterial embolization (TAE) therapy for more than 4 months before the PET study. One hour after injection of 18F-FDG, a whole-body scan was performed. In addition, delayed imaging focusing on the liver was also performed 2 h and 3 h after the injection. The standard uptake value (SUV) was calculated for the tumours in each image.
Results: The twelve patients had 16 HCCs. Of the 16 HCCs, nine were detected by 18F-FDG-PET scans based on the 1 h images, whereas 10 HCCs were detected based on the 2 or 3 h images. The diagnostic sensitivity increased from 56.3% on the 1 h image to 62.5% on the 2 and 3 h images. In addition, the mean SUV increased from 3.63 at 1 h to 3.86 at 2 h and 3.99 at 3 h after the injection of 18F-FDG. On the other hand, the mean SUV in the normal liver tissue decreased slightly from 2.38 at 1 h to 2.33 at 2 h and 2.31 at 3 h. The tumour to normal liver tissue (T/N) ratio increased from 1.56 at 1 h to 1.68 at 2 h and 1.75 at 3 h.
Conclusion: In the evaluation of HCC, delayed 2 and 3 h imaging can detect more lesions than standard 1 h imaging. Imaging at 3 h has a better T/N ratio than imaging at 2 h, but does not increase the diagnostic sensitivity.