One-tenth-activity total-body positron emission tomography versus full-activity imaging in patients with a complex of hepatic malignant tumors: a retrospective study

Background: The value of ultra-low-activity 2-[F-18]-fluoro-2-deoxy-D-glucose (F-18-FDG) positron emission tomography (PET) imaging in patients with hepatic malignancies remains unclear.Methods: A cross-sectional study was conducted from April 2019 to May 2021 in Zhongshan Hospital, Fudan University. A total of 49 patients with hepatic malignancies, including hepatocellular carcinoma (HCC) (n=13) or intrahepatic cholangiocarcinoma (ICC) (n=36), underwent 60-min dynamic PET imaging, with 15 undergoing full-activity F-18-FDG and 34 undergoing ultra-low-activity F-18-FDG. The kinetic metrics (K-1-k(3), and K-i) of tumors were calculated and compared between the activity groups. Another 54 patients (27 each group) with hepatic malignancies, including HCC (n=9), ICC (n=34), and metastases (n=11), underwent static imaging. Image qualities were compared between the groups in terms of 5-point Likert scores (with a score >= 3 fulfilling the clinical requirement), the mean standardized uptake value (SUVmean), the standard deviation of standardized uptake value (SUVSD), and the signal-to-noise ratio (SNR) of the liver; the SUVmean of blood pool and muscle; and the tumor-to-liver ratio (TLR), tumor-to-blood ratio (TBR), and tumor-to-muscle ratio (TMR) of lesions. Intergroup comparisons were performed using Chi-squared test for categorical variables and the Student's t-test or the Mann-Whitney test for continuous variables depending on the normality of variables.Results: There was a nonsignificant difference in the kinetic metrics (K-1-k(3), and K-i) of tumors between the activity groups. In static imaging, 1-min full-activity (F-1) and 8-min ultra-low-activity (L-8) images obtained image-quality scores >3 and were thus selected for intergroup comparisons. Nonsignificant differences in SUVmean of liver, blood pool, and muscle were identified between F-1 and L-8 images (P=0.641, P=0.542, and P=0.073, respectively) although the liver SNR was slightly higher in F-1 (13.10 vs. 11.31; P=0.003). Lesion detectability was 98.5% and 100% for F-1 and L-8 images, respectively, but there were no significant differences in TLR, TBR, or TMR between the groups.Conclusions: The results of this single-center study indicate that the performance of ultra-low-activity PET imaging is comparable to that of full-activity imaging in patients with hepatic malignancies.