Semiquantitative Analysis of the Biodistribution of the Combined 18F-NaF and 18F-FDG Administration for PET/CT Imaging

In this study, we evaluated the biodistribution of the F-18(-)/F-18-FDG administration, compared with separate F-18-NaF and F-18-FDG administrations. We also estimated the interaction of F-18-NaF and F-18-FDG in the F-18(-)/F-18-FDG administration by semiquantitative analysis. Methods: We retrospectively analyzed the data of 49 patients (39 men, 10 women; mean age +/- SD, 59.3 +/- 15.2 y) who underwent separate F-18-FDG PET/CT and F-18-NaF PET/CT scans as well as F-18(-)/F-18-FDG PET/CT sequentially. The most common primary diagnosis was prostate cancer (n = 28), followed by sarcoma (n = 9) and breast cancer (n = 6). The mean standardized uptake values (SUVs) were recorded for 18 organs in all patients, and maximum SUV and mean SUV were recorded for all the identified malignant lesions. We also estimated the F-18(-)/F-18-FDG uptake as the sum of F-18-FDG uptake and adjusted F-18-NaF uptake based on the ratio of F-18-NaF injected dose in F-18(-)/F-18-FDG PET/CT. Lastly, we compared the results to explore the interaction of F-18-FDG and F-18-NaF uptake in the F-18(-)/F-18-FDG scan. Results: The F-18(-)/F-18-FDG uptake in the cerebral cortex, cerebellum, parotid grand, myocardium, and bowel mostly reflected the F-18-FDG uptake, whereas the uptake in the other analyzed structures was influenced by both the F-18-FDG and the F-18-NaF uptake. The F-18(-)/F-18-FDG uptake in extraskeletal lesions showed no significant difference when compared with the uptake from the separate F-18-FDG scan. The F-18(-)/F-18-FDG uptake in skeletal lesions reflected mostly the F-18-NaF uptake. The tumor-to-background ratio of F-18(-)/F-18-FDG in extraskeletal lesions showed no significant difference when compared with that from F-18-FDG alone (P < 0.73). For skeletal lesions, the tumor-to-background ratio of F-18(-)/F-18-FDG was lower than that from F-18-NaF alone (P < 0.001); however, this difference did not result in missed skeletal lesions on the F-18(-)/F-18-FDG scan. Conclusion: The understanding of the biodistribution of radiopharmaceuticals and the lesion uptake of the F-18(-)/F-18-FDG scan as well as the variations compared with the uptake on the separate F-18-FDG PET/CT and F-18-NaF PET/CT are valuable for more in-depth evaluation of the combined scanning technique.