Physiological biodistribution of 18F-fluciclovine PET in the head: as a baseline for interpretation in patients with suspected glioma

Introduction Anti-1-amino-3-[ 18 F] fluorocyclobutane-1-carboxylic acid ( 18 F-fluciclovine; anti-3-[ 18 F] FACBC) is an amino acid positron emission tomography (PET) tracer used for the evaluation of brain tumors in cases of suspected or diagnosed glioma. While its uptake characteristics in brain tumors have been reported, systematic data on background uptake in normal-appearing head tissues including extracranial structures remain limited. The purpose of this study was to characterize the background uptake of 18 F-fluciclovine in intracranial and extracranial head tissues in patients with suspected malignant glioma. Methods 18 F-fluciclovine PET/CT images from 20 patients with suspected malignant glioma were retrospectively analyzed. Standardized uptake values (SUVs) were measured in 24 predefined head regions, and inter-regional differences were assessed using one-way ANOVA with Tukey's HSD post hoc test. Time–activity curves were generated in 15 patients for dynamic evaluation of temporal uptake patterns. In the overall cohort, 8 patients also underwent 11 C-methionine PET/CT, and SUVs were compared using paired t-tests and their correlations were assessed using Pearson's correlation coefficient. Statistical significance was set at P < 0.05. Results 18 F-fluciclovine uptake in the cerebral hemispheres was generally low, with the lowest SUV mean observed in white matter (0.15 ± 0.04). Cortical uptake was uniformly low, with SUV mean and SUV peak of 0.28 ± 0.06 and 0.31 ± 0.07, respectively, and no significant interlobar differences. Among other brain regions, SUV mean was highest in the cerebellar vermis (0.46 ± 0.09), followed by the pons, cerebellum, thalamus/basal ganglia, midbrain, and medulla. Dynamic imaging demonstrated low and stable brain uptake, whereas the pituitary and parotid glands exhibited early peak uptake followed by washout. In patients who also underwent 11 C-methionine PET, 11 C-methionine showed significantly higher uptake in all brain regions, whereas 18 F-fluciclovine was higher in venous structures, skeletal muscle, and the nasal cavity. Conclusion This study establishes a detailed baseline of background 18 F-fluciclovine uptake in normal-appearing intracranial and extracranial head tissues in patients with suspected glioma. These findings may facilitate the distinction between physiological and pathological uptake and inform the interpretation of 18 F-fluciclovine PET in the assessment of brain tumors.